1Journal Vitae | https://revistas.udea.edu.co/index.php/vitaeVolume 29 | Number 03 | Article 350572
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
JOURNAL VITAE
School of Pharmaceutical and
Food Sciences
ISSN 0121-4004 | ISSNe 2145-2660
University of Antioquia
Medellin, Colombia
Filliations
1 Universidad Nacional de Colombia
–Sede Bogotá – Facultad de
Ingeniería - Departamento de
Ingeniería Química y Ambiental
– Carrera 30 # 45-03 Edificio 453,
Bogotá D.C, 111321 –Colombia.
2 Universidad Nacional de Colombia –
Sede Bogotá –Instituto de Ciencia
y Tecnología de Alimentos–Carrera
30 # 45-03 Edificio 500A, Bogotá
D.C, 111321 –Colombia.
3 Universidad Nacional de Colombia
–Sede Bogotá –Facultad de
Ciencias Agrarias – Departamento
de Desarrollo Rural y
Agroalimentario –Carrera 30 #
45-03 Edificio 500, 13Bogotá D.C,
111321 – (+57) 601 316 50 00
ext.19128 – Colombia.
*Corresponding
Carlos Mario Zuluaga-Domínguez
cmzuluagad@unal.edu.co
Received: 25 July 2022
Accepted: 08 October 2022
Published: 17 October 2022
Effects of Solar Drying on the Structural and
Thermodynamic Characteristics of Bee Pollen
Efectos del secado solar sobre las características
estructurales y termodinámicas del polen apícola
Bryan Alberto Castellanos-Paez1 , Andrés Durán-Jiménez1 , Carlos Alberto
Fuenmayor2 , Marta Cecilia Quicazán2 , Carlos Mario Zuluaga-Domínguez3*
ABSTRACT
Background: Bee pollen is a natural product collected and transformed by bees, intended for
human consumption, given its nutritional and bioactive richness. The fundamental operation
of adequacy is drying, which allows its preservation, avoiding chemical or microbiological
degradation, typically using tray dryers with hot air that use electricity or fuel for heat
generation. Solar drying is an alternative that uses radiation as an energy source. However, it
should be ensured that this type of process guarantees the quality of the product while not
degrading its properties and, therefore, maintaining its morphological integrity. Objective:
to establish the effect of solar drying on bee pollen structure compared to the conventional
cabin dehydration process. Methods: Bee pollen was dehydrated using two types of dryers:
a solar dryer and a forced convection oven. The solar dryer operating conditions were an
average temperature of 19-35 °C with a maximum of 38 °C and average relative humidity
(RH) of 55 %. Cabin dryer operating conditions were a set point temperature of 55 ± 2 °C and
10 % RH average humidity. The morphologic and thermodynamic properties of dried bee
pollen, such as phase transition enthalpy through Differential Scanning Calorimetry (DSC),
porosity and surface area through surface area analysis, and microscopic surface appearance
by Scanning Electron Microscopy (SEM), were measured. Results: The results showed dry bee
pollen, both in the cabin dryer and solar dryer, did not suffer morphological changes seen
through SEM compared to fresh bee pollen. Moreover, surface area analysis indicated the
absence of porosity in the microscopic or macroscopic structure, demonstrating that solar or
cabin drying processes did not affect the specific surface area concerning fresh bee pollen.
Additionally, Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA)
showed that endothermic phase transitions for dried bee pollen by cabin or solar dryer were
at 145 °C and 160 °C, respectively. This can be mostly associated with free water loss due
to the morphological structure preservation of the material compared to fresh bee pollen.
Conclusion: These results demonstrate that solar drying is a reliable alternative to bee pollen
dehydration as there were no effects that compromised its structural integrity.
Keywords: Conservation processes, beekeeping, bee pollen, quality, dehydration.
ORIGINAL RESEARCH
Published 17 October 2022
Doi: https://doi.org/10.17533/udea.vitae.v29n3a350572
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
JOURNAL VITAE
School of Pharmaceutical and
Food Sciences
ISSN 0121-4004 | ISSNe 2145-2660
University of Antioquia
Medellin, Colombia
Filliations
1 Universidad Nacional de Colombia
–Sede Bogotá – Facultad de
Ingeniería - Departamento de
Ingeniería Química y Ambiental
– Carrera 30 # 45-03 Edificio 453,
Bogotá D.C, 111321 –Colombia.
2 Universidad Nacional de Colombia –
Sede Bogotá –Instituto de Ciencia
y Tecnología de Alimentos–Carrera
30 # 45-03 Edificio 500A, Bogotá
D.C, 111321 –Colombia.
3 Universidad Nacional de Colombia
–Sede Bogotá –Facultad de
Ciencias Agrarias – Departamento
de Desarrollo Rural y
Agroalimentario –Carrera 30 #
45-03 Edificio 500, 13Bogotá D.C,
111321 – (+57) 601 316 50 00
ext.19128 – Colombia.
*Corresponding
Carlos Mario Zuluaga-Domínguez
cmzuluagad@unal.edu.co
Received: 25 July 2022
Accepted: 08 October 2022
Published: 17 October 2022
Effects of Solar Drying on the Structural and
Thermodynamic Characteristics of Bee Pollen
Efectos del secado solar sobre las características
estructurales y termodinámicas del polen apícola
Bryan Alberto Castellanos-Paez1 , Andrés Durán-Jiménez1 , Carlos Alberto
Fuenmayor2 , Marta Cecilia Quicazán2 , Carlos Mario Zuluaga-Domínguez3*
ABSTRACT
Background: Bee pollen is a natural product collected and transformed by bees, intended for
human consumption, given its nutritional and bioactive richness. The fundamental operation
of adequacy is drying, which allows its preservation, avoiding chemical or microbiological
degradation, typically using tray dryers with hot air that use electricity or fuel for heat
generation. Solar drying is an alternative that uses radiation as an energy source. However, it
should be ensured that this type of process guarantees the quality of the product while not
degrading its properties and, therefore, maintaining its morphological integrity. Objective:
to establish the effect of solar drying on bee pollen structure compared to the conventional
cabin dehydration process. Methods: Bee pollen was dehydrated using two types of dryers:
a solar dryer and a forced convection oven. The solar dryer operating conditions were an
average temperature of 19-35 °C with a maximum of 38 °C and average relative humidity
(RH) of 55 %. Cabin dryer operating conditions were a set point temperature of 55 ± 2 °C and
10 % RH average humidity. The morphologic and thermodynamic properties of dried bee
pollen, such as phase transition enthalpy through Differential Scanning Calorimetry (DSC),
porosity and surface area through surface area analysis, and microscopic surface appearance
by Scanning Electron Microscopy (SEM), were measured. Results: The results showed dry bee
pollen, both in the cabin dryer and solar dryer, did not suffer morphological changes seen
through SEM compared to fresh bee pollen. Moreover, surface area analysis indicated the
absence of porosity in the microscopic or macroscopic structure, demonstrating that solar or
cabin drying processes did not affect the specific surface area concerning fresh bee pollen.
Additionally, Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA)
showed that endothermic phase transitions for dried bee pollen by cabin or solar dryer were
at 145 °C and 160 °C, respectively. This can be mostly associated with free water loss due
to the morphological structure preservation of the material compared to fresh bee pollen.
Conclusion: These results demonstrate that solar drying is a reliable alternative to bee pollen
dehydration as there were no effects that compromised its structural integrity.
Keywords: Conservation processes, beekeeping, bee pollen, quality, dehydration.
ORIGINAL RESEARCH
Published 17 October 2022
Doi: https://doi.org/10.17533/udea.vitae.v29n3a350572
2Journal Vitae | https://revistas.udea.edu.co/index.php/vitae Volume 29 | Number 03 | Article 350572Bryan Alberto Castellanos-Paez, Andrés Durán-Jiménez, Carlos Alberto Fuenmayor, Marta Cecilia Quicazán, Carlos Mario Zuluaga-Domínguez
1. INTRODUCTION
Over the last few decades, drying alternatives
have been proposed to take advantage of
natural energy sources, such as solar drying.
With this type of drying, it is possible to reduce
the moisture content of foods and generate an
antimicrobial effect due to ultraviolet radiation
(1–4). In general, solar drying uses natural air
convection for dehydration, and thus, it should
be controlled according to the climatic conditions
of the area (5–8). This means that operation
should be performed in time intervals where
the dry bulb temperature and relative humidity
within the dryer are high and low, respectively,
compared to the environmental conditions
to avoid reaching the dew temperature and,
therefore, the air saturation, which can affect
the drying efficacy of the material of interest
(9). On the one hand, the high surface area
is a desired characteristic of the wet product
(to be dried). In contrast, low hygroscopicity
and low degradation of bioactive compounds
are desired characteristics of the already dried
product. (10, 11). In this sense, attributes such
as porosity, phase transition temperatures (e.g.,
fusions, vitreous transitions, volatilizations),
component degradation, specific surface area,
and structural shape, among others, can provide
information about the effect of solar drying on
food, and allow rapid comparison with another
drying (12). According to previous studies, the
effect of solar drying on the physicochemical,
biological composition, and moisture of different
plant food matrices has been analyzed, finding,
in some cases, a slight decrease in compounds
such as proteins, lipids, fiber, and carbohydrates
(10, 13). Concerning biological composition, it
is reported that there are decreases in aerobic
mesophylls, Escherichia coli, fungi, and yeasts (7,
8). Regarding moisture, it reaches equilibrium
values of 4-8 % (dry base) after six hours of
drying at air temperatures between 40 °C and
42 °C but this applies to geographi cal regions
where the temperature inside and outside
the solar dryer is kept approximately constant
during drying (also with an inside temperature
higher than the outside temperature), and
the vapor pressure in the air is lower than
the vapor pressure due to the moisture held
inside the product. Otherwise, the equilibrium
moisture content in the product will change
depending on these weather conditions (14,
15). Regarding antioxidant compounds, solar
RESUMEN
Antecedentes: El polen apícola es un producto natural recolectado y transformado por las abejas. La operación fundamental
de adecuación del polen es el secado, lo que permite su conservación, evitando su degradación química o microbiológica,
típicamente se utilizan secadores de bandejas con aire caliente que emplean electricidad o combustibles para la generación de
calor. El secado solar es una alternativa que utiliza la radiación solar como fuente de energía. Sin embargo, se debe garantizar
que este tipo de proceso asegure la calidad del producto a la vez que no degrade sus propiedades, manteniendo su integridad
morfológica. Objetivo: Establecer el efecto del secado solar sobre la estructura del polen apícola en comparación al proceso
convencional de deshidratación en cabina. Métodos: El polen de abeja se deshidrató utilizando dos tipos de secadores: secador
solar y horno de convención forzada. Las condiciones de operación del secador solar fueron una temperatura promedio de 19-
45 °C con un máximo de 38 °C y una humedad relativa (HR) promedio de 55 %. Las condiciones de operación del secador de
cabina fueron una temperatura de referencia de 55 ± 2 °C y una humedad promedio de 10 % HR. Se midieron las propiedades
morfológicas y termodinámicas del polen de abeja desecado, como la entalpía de transición de fase mediante calorimetría
diferencial de barrido (DSC), la porosidad y el área superficial mediante análisis de área superficial y el aspecto microscópico de
la superficie mediante microscopía electrónica de barrido (SEM). Resultados: Los resultados mostraron que el polen seco tanto
en el secador de cabina como en el secador solar muestra que no sufrió cambios morfológicos vistos a través de Microscopía
Electrónica de Barrido y en comparación con el polen fresco de abeja, además un análisis de sortometría indicó la ausencia
de porosidad en la estructura microscópica y macroscópica, lo que indica que los procesos de secado solar o en cabina no
tuvieron efectos sobre el área superficial específica con respecto al polen fresco de las abejas. En adición, los resultados de
calorimetría diferencial de barrido (DSC) y análisis termogravimétrico (TGA) muestran que las transiciones de fase endotérmicas
para el polen seco tanto en secado de cabina como solar fueron a 145 °C y 160 °C, que puede asociarse mayormente a la
pérdida de agua libre, debido a la conservación de la estructura morfológica del material y en comparación al polen fresco.
Conclusión: Estos resultados demuestran que el secado solar es una alternativa viable para la deshidratación del polen al no
existir efectos que comprometan su integridad estructural.
Palabras clave: Procesos de conservación, apicultura, polen de abeja, calidad, deshidratación.
1. INTRODUCTION
Over the last few decades, drying alternatives
have been proposed to take advantage of
natural energy sources, such as solar drying.
With this type of drying, it is possible to reduce
the moisture content of foods and generate an
antimicrobial effect due to ultraviolet radiation
(1–4). In general, solar drying uses natural air
convection for dehydration, and thus, it should
be controlled according to the climatic conditions
of the area (5–8). This means that operation
should be performed in time intervals where
the dry bulb temperature and relative humidity
within the dryer are high and low, respectively,
compared to the environmental conditions
to avoid reaching the dew temperature and,
therefore, the air saturation, which can affect
the drying efficacy of the material of interest
(9). On the one hand, the high surface area
is a desired characteristic of the wet product
(to be dried). In contrast, low hygroscopicity
and low degradation of bioactive compounds
are desired characteristics of the already dried
product. (10, 11). In this sense, attributes such
as porosity, phase transition temperatures (e.g.,
fusions, vitreous transitions, volatilizations),
component degradation, specific surface area,
and structural shape, among others, can provide
information about the effect of solar drying on
food, and allow rapid comparison with another
drying (12). According to previous studies, the
effect of solar drying on the physicochemical,
biological composition, and moisture of different
plant food matrices has been analyzed, finding,
in some cases, a slight decrease in compounds
such as proteins, lipids, fiber, and carbohydrates
(10, 13). Concerning biological composition, it
is reported that there are decreases in aerobic
mesophylls, Escherichia coli, fungi, and yeasts (7,
8). Regarding moisture, it reaches equilibrium
values of 4-8 % (dry base) after six hours of
drying at air temperatures between 40 °C and
42 °C but this applies to geographi cal regions
where the temperature inside and outside
the solar dryer is kept approximately constant
during drying (also with an inside temperature
higher than the outside temperature), and
the vapor pressure in the air is lower than
the vapor pressure due to the moisture held
inside the product. Otherwise, the equilibrium
moisture content in the product will change
depending on these weather conditions (14,
15). Regarding antioxidant compounds, solar
RESUMEN
Antecedentes: El polen apícola es un producto natural recolectado y transformado por las abejas. La operación fundamental
de adecuación del polen es el secado, lo que permite su conservación, evitando su degradación química o microbiológica,
típicamente se utilizan secadores de bandejas con aire caliente que emplean electricidad o combustibles para la generación de
calor. El secado solar es una alternativa que utiliza la radiación solar como fuente de energía. Sin embargo, se debe garantizar
que este tipo de proceso asegure la calidad del producto a la vez que no degrade sus propiedades, manteniendo su integridad
morfológica. Objetivo: Establecer el efecto del secado solar sobre la estructura del polen apícola en comparación al proceso
convencional de deshidratación en cabina. Métodos: El polen de abeja se deshidrató utilizando dos tipos de secadores: secador
solar y horno de convención forzada. Las condiciones de operación del secador solar fueron una temperatura promedio de 19-
45 °C con un máximo de 38 °C y una humedad relativa (HR) promedio de 55 %. Las condiciones de operación del secador de
cabina fueron una temperatura de referencia de 55 ± 2 °C y una humedad promedio de 10 % HR. Se midieron las propiedades
morfológicas y termodinámicas del polen de abeja desecado, como la entalpía de transición de fase mediante calorimetría
diferencial de barrido (DSC), la porosidad y el área superficial mediante análisis de área superficial y el aspecto microscópico de
la superficie mediante microscopía electrónica de barrido (SEM). Resultados: Los resultados mostraron que el polen seco tanto
en el secador de cabina como en el secador solar muestra que no sufrió cambios morfológicos vistos a través de Microscopía
Electrónica de Barrido y en comparación con el polen fresco de abeja, además un análisis de sortometría indicó la ausencia
de porosidad en la estructura microscópica y macroscópica, lo que indica que los procesos de secado solar o en cabina no
tuvieron efectos sobre el área superficial específica con respecto al polen fresco de las abejas. En adición, los resultados de
calorimetría diferencial de barrido (DSC) y análisis termogravimétrico (TGA) muestran que las transiciones de fase endotérmicas
para el polen seco tanto en secado de cabina como solar fueron a 145 °C y 160 °C, que puede asociarse mayormente a la
pérdida de agua libre, debido a la conservación de la estructura morfológica del material y en comparación al polen fresco.
Conclusión: Estos resultados demuestran que el secado solar es una alternativa viable para la deshidratación del polen al no
existir efectos que comprometan su integridad estructural.
Palabras clave: Procesos de conservación, apicultura, polen de abeja, calidad, deshidratación.
3Journal Vitae | https://revistas.udea.edu.co/index.php/vitaeVolume 29 | Number 03 | Article 350572
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
drying promotes the increase specifically in total
phenols and flavonoids in plant food matrices
(16, 17). The effects on the thermodynamic and
morphological properties of plant matrices
report mass losses of less than 10 % at nearly
100 °C associated with dehydration, mass losses
of 60 % after 180 °C due to degradation and
volatilization of compounds in addition to changes
in morphological structure, density, and pore size
distribution (18, 19).
Bee pollen is the agglomerate of gametes from
flowers collected by worker bees and mixed with
nectar, honey, and salivary fluids and then packaged
in honeycomb cells in the hive. It is also collected by
bees related to the Apis mellifera species, serving
as the hive’s nutritional source of protein and
lipids. Bee pollen is constituted by fine microscopic
particles of variable sizes and shapes (20 μm – 45
μm), agglomerated in the form of spherical pellets
(12, 21, 22). The nutritional composition is mainly
determined by carbohydrates (40 %), proteins (23 %),
lipids (6 %), vitamins (2 %), phenolic compounds,
and other bioactive compounds (2 %) on a dry basis
(23, 24), which makes it nutritious for the human diet
and gives it possible beneficial health effects (25,
26). However, due to its high nutritional content
and high moisture value at harvest time, it is a
product highly susceptible to contamination and
the growth of microorganisms, then it is necessary
to apply processes such as drying to prevent its
deterioration (21, 23). Conventionally, bee pollen
is subjected to dehydration, preferably through
forced convection drying with temperature control
(17) instead of sun drying, mainly due to cultural
factors and false beliefs that attribute adverse
effects to bee pollen when exposed to the sun. On
the contrary, solar drying represents a cost-cutting
alternative instead of electricity (8). Nevertheless,
in the literature, there is little information available
for this type of characterization in beekeeping
products; consequently, this is one of the first works
that focus on evaluating the true effects of heat
treatment in a solar dryer on the physical structure
of bee pollen. For this reason, the aim set out in this
work was to analyze the effects of solar drying on
the morphology, and the thermogravimetric and
calorimetric properties of bee pollen compared
to conventional cabin dehydration processes. The
results are valuable to strengthen the industrial use
of solar drying as an alternative to cabin drying due
to its low operating cost, which benefits beekeepers
given the reduction of energy consumption.
2. MATERIAL AND METHODS
2.1. Samples
Bee pollen samples were collected from Viracachá,
Boyacá, Colombia (Coordinates: 5° 26’ 11”N 73°
17’ 46”O) between January and March 2019. After
collection, the samples were sieved to remove
the largest impurities (solid waste, animals, and
vegetation) with a Tyler series mesh #6. Afterward,
fresh bee pollen was hermetically packaged in 250 g
opaque glass containers and stored in a dark room
at 25 °C until testing.
2.2 Methods
2.2.1 Solar drying tests
The bee pollen was arranged in stainless steel metal
trays with 2 mm perforations, with dimensions 1.5
m long and 1 m wide, adding a 1 cm layer of bee
pollen for uniform dehydration over time. Available
sunlight in the study area typically ranged from 8
am to 5 pm, and natural convection of the air inside
the solar dryer was used. Samples of 250 g were
taken every hour until nine hours of dehydration.
In addition, dry bulb temperature and relative air
humidity data were recorded inside the dryer with
a digital thermohygrometer at three different points
of the dryer and at the same height as the position
of the trays (90 cm from the ground).
2.2.2 Cabin drying
The bee pollen was arranged in stainless steel metal
trays with perforations of 2 mm, with dimensions of
1.2 m long and 0.8 m wide, adding a 1 cm layer of
bee pollen in the tray to have uniform dehydration,
using a forced convection oven. The dry bulb
temperature was 55 °C ± 2 °C and drying lasted
nine hours. Samples of 250 g of pollen were taken
at the end of drying.
2.2.3 Performed analyses for bee pollen
2.2.3.1. Scanning Electron Microscopy (SEM)
Ten g samples of dried and fresh pollen (<0.1 mm)
were weighed and coated with a layer of 2 mm gold.
The measurement was performed on a Quanta
200 (Thermo Fisher Scientific, Oregon) using a
secondary electron collector and a working distance
(collector) of 10.3 mm. The test was performed
under vacuum and at a stable temperature of 18°C.
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
drying promotes the increase specifically in total
phenols and flavonoids in plant food matrices
(16, 17). The effects on the thermodynamic and
morphological properties of plant matrices
report mass losses of less than 10 % at nearly
100 °C associated with dehydration, mass losses
of 60 % after 180 °C due to degradation and
volatilization of compounds in addition to changes
in morphological structure, density, and pore size
distribution (18, 19).
Bee pollen is the agglomerate of gametes from
flowers collected by worker bees and mixed with
nectar, honey, and salivary fluids and then packaged
in honeycomb cells in the hive. It is also collected by
bees related to the Apis mellifera species, serving
as the hive’s nutritional source of protein and
lipids. Bee pollen is constituted by fine microscopic
particles of variable sizes and shapes (20 μm – 45
μm), agglomerated in the form of spherical pellets
(12, 21, 22). The nutritional composition is mainly
determined by carbohydrates (40 %), proteins (23 %),
lipids (6 %), vitamins (2 %), phenolic compounds,
and other bioactive compounds (2 %) on a dry basis
(23, 24), which makes it nutritious for the human diet
and gives it possible beneficial health effects (25,
26). However, due to its high nutritional content
and high moisture value at harvest time, it is a
product highly susceptible to contamination and
the growth of microorganisms, then it is necessary
to apply processes such as drying to prevent its
deterioration (21, 23). Conventionally, bee pollen
is subjected to dehydration, preferably through
forced convection drying with temperature control
(17) instead of sun drying, mainly due to cultural
factors and false beliefs that attribute adverse
effects to bee pollen when exposed to the sun. On
the contrary, solar drying represents a cost-cutting
alternative instead of electricity (8). Nevertheless,
in the literature, there is little information available
for this type of characterization in beekeeping
products; consequently, this is one of the first works
that focus on evaluating the true effects of heat
treatment in a solar dryer on the physical structure
of bee pollen. For this reason, the aim set out in this
work was to analyze the effects of solar drying on
the morphology, and the thermogravimetric and
calorimetric properties of bee pollen compared
to conventional cabin dehydration processes. The
results are valuable to strengthen the industrial use
of solar drying as an alternative to cabin drying due
to its low operating cost, which benefits beekeepers
given the reduction of energy consumption.
2. MATERIAL AND METHODS
2.1. Samples
Bee pollen samples were collected from Viracachá,
Boyacá, Colombia (Coordinates: 5° 26’ 11”N 73°
17’ 46”O) between January and March 2019. After
collection, the samples were sieved to remove
the largest impurities (solid waste, animals, and
vegetation) with a Tyler series mesh #6. Afterward,
fresh bee pollen was hermetically packaged in 250 g
opaque glass containers and stored in a dark room
at 25 °C until testing.
2.2 Methods
2.2.1 Solar drying tests
The bee pollen was arranged in stainless steel metal
trays with 2 mm perforations, with dimensions 1.5
m long and 1 m wide, adding a 1 cm layer of bee
pollen for uniform dehydration over time. Available
sunlight in the study area typically ranged from 8
am to 5 pm, and natural convection of the air inside
the solar dryer was used. Samples of 250 g were
taken every hour until nine hours of dehydration.
In addition, dry bulb temperature and relative air
humidity data were recorded inside the dryer with
a digital thermohygrometer at three different points
of the dryer and at the same height as the position
of the trays (90 cm from the ground).
2.2.2 Cabin drying
The bee pollen was arranged in stainless steel metal
trays with perforations of 2 mm, with dimensions of
1.2 m long and 0.8 m wide, adding a 1 cm layer of
bee pollen in the tray to have uniform dehydration,
using a forced convection oven. The dry bulb
temperature was 55 °C ± 2 °C and drying lasted
nine hours. Samples of 250 g of pollen were taken
at the end of drying.
2.2.3 Performed analyses for bee pollen
2.2.3.1. Scanning Electron Microscopy (SEM)
Ten g samples of dried and fresh pollen (<0.1 mm)
were weighed and coated with a layer of 2 mm gold.
The measurement was performed on a Quanta
200 (Thermo Fisher Scientific, Oregon) using a
secondary electron collector and a working distance
(collector) of 10.3 mm. The test was performed
under vacuum and at a stable temperature of 18°C.
4Journal Vitae | https://revistas.udea.edu.co/index.php/vitae Volume 29 | Number 03 | Article 350572Bryan Alberto Castellanos-Paez, Andrés Durán-Jiménez, Carlos Alberto Fuenmayor, Marta Cecilia Quicazán, Carlos Mario Zuluaga-Domínguez
The working voltage was 30 kV with a magnification
of 6000x (27, 28).
2.2.3.2. Differential Scanning Calorimetry (DSC)
The test was performed on a 40 μL capsule
where 5 to 7 mg of either dried or fresh pollen
samples were added, with a dynamic temperature
segment of 0 °C to 200. °C, with an increment
rate of 12 °C/min. Additionally, the atmosphere
of use was nitrogen with a flow of 50 μL/min. The
measurement was performed on a DSC 1 – Star
System calorimeter (29).
2.2.3.3. Surface area analysis
Initially, the dried and fresh bee pollen was milled
until it passed through a mesh of the Tyler series
# 80. Subsequently, 10 mg of the sample was
weighed and degassed in aluminum-coated ceramic
chambers where a vacuum up to 76 mmHg was used
for 50 hours to ensure the removal of gases on the
surface. The sample was placed inside an adsorption
chamber at 30°C, using nitrogen as a drag gas. The
area of the BET monolayer (Brunauer-Emmett-Teller)
was calculated, performing the same analysis for
the entire bee pollen. The equipment used was a
Gemini 2375 surface area analyzer (30).
2.2.3.4 Thermogravimetric Analysis (TGA)
The test was conducted with a sample of 10 mg
of dried and fresh bee pollen in an inert nitrogen
atmosphere with a flow of 40 μL/min using a dynamic
range of 10 °C/min and a controlled temperature
between 0 °C and 200 °C for the determination of
volatile compounds. A reactive oxygen atmosphere
was used for combustion in a dynamic temperature
range between 0 °C and 700 °C. A TGA-DSC 1 Star-
System equipment was used (29).
2.2.3.5 Environmental measures
Luminosity intensity (Lux), relative humidity (%), solar
dryer temperature (°C) and room temperature (°C)
were measured in triplicate on two different dates.
Pyranometer UEI DLM2 light meter was used to
measure luminosity intensity at the inlet and mid-
height of the dryer. Digital thermometer EBCHQ (ref:
94196) was used to measure relative humidity and
temperature inlet and outlet from the dryer and at
mid-height of the dryer.
2.2.3.6 Statistical analysis
The data related to environmental measures, DSC,
TGA, and surface area analysis were performed in
triplicate. Statistical analysis was performed using a
one-way ANOVA test complemented by The Tukey
test with a significance level of 95 %. The analysis
was carried out using Statistix ® and Microsoft Excel®
.
3. RESULTS AND DISCUSSION
3.1 Effect of solar drying on pollen grain
morphology
Figure 1 shows the effect of the solar drying process on
the morphology of two characteristic palynomorphs
of bee pollen used in this study, compared to the
effect of a conventional drying process (cabin drying
by forced air convection), evaluated through SEM.
The pollinic structures (A) and (A’) correspond to
fresh bee pollen grains of spiculate and cross-
linked palynomorphs, respectively. Palynomorph
(A) belongs to the Asteraceae family, while (A’)
belongs to the Escallonia pendula family (31). The
structures (B) and (B’) correspond to the same
palynomorphs after solar drying, and the structures
(C) and (C’) correspond to the palynomorphs after
cabin drying. Regarding spiculate palynomorphs
(A, B, C), it can be seen they have a spherical shape
with macropores and hairs that make up the typical
pollinic structure of Asteraceae. Minor changes are
observed in the form of the exine of fresh pollen
grains (A), after solar drying (B), and in the cabin
(C). In this fresh palynomorph (A), it is appreciated
that macropores are deeper than in (B) and (C). It
is important to mention that the exine corresponds
to the outer layer of the bee pollen grain, which
is composed mainly of sporopollenin, resistant to
hydrolytic enzymes and some chemical solvents.
This compound is not currently known in detail, but
it is known that its conformation is mainly given by
compounds similar to lignin, ethers, esters, cross-
linked lipids, and cinnamic acid derivatives (12). In
previous studies of drying, microencapsulation,
and fermentation, it has been observed some
changes in exine occurred at high temperatures
and/or radiation (12, 32–34), where at temperatures
above 136 °C there is the formation of alkanes,
alkylphenols, and alkenes, however, since drying
processes occur at an average temperature close to
50 °C, and there is no greater effect on the exine.
On the other hand, the hairs of the fresh spiculate
palynomorph (A) are thicker and present in greater
quantity than in structures (B) and (C). It can be
The working voltage was 30 kV with a magnification
of 6000x (27, 28).
2.2.3.2. Differential Scanning Calorimetry (DSC)
The test was performed on a 40 μL capsule
where 5 to 7 mg of either dried or fresh pollen
samples were added, with a dynamic temperature
segment of 0 °C to 200. °C, with an increment
rate of 12 °C/min. Additionally, the atmosphere
of use was nitrogen with a flow of 50 μL/min. The
measurement was performed on a DSC 1 – Star
System calorimeter (29).
2.2.3.3. Surface area analysis
Initially, the dried and fresh bee pollen was milled
until it passed through a mesh of the Tyler series
# 80. Subsequently, 10 mg of the sample was
weighed and degassed in aluminum-coated ceramic
chambers where a vacuum up to 76 mmHg was used
for 50 hours to ensure the removal of gases on the
surface. The sample was placed inside an adsorption
chamber at 30°C, using nitrogen as a drag gas. The
area of the BET monolayer (Brunauer-Emmett-Teller)
was calculated, performing the same analysis for
the entire bee pollen. The equipment used was a
Gemini 2375 surface area analyzer (30).
2.2.3.4 Thermogravimetric Analysis (TGA)
The test was conducted with a sample of 10 mg
of dried and fresh bee pollen in an inert nitrogen
atmosphere with a flow of 40 μL/min using a dynamic
range of 10 °C/min and a controlled temperature
between 0 °C and 200 °C for the determination of
volatile compounds. A reactive oxygen atmosphere
was used for combustion in a dynamic temperature
range between 0 °C and 700 °C. A TGA-DSC 1 Star-
System equipment was used (29).
2.2.3.5 Environmental measures
Luminosity intensity (Lux), relative humidity (%), solar
dryer temperature (°C) and room temperature (°C)
were measured in triplicate on two different dates.
Pyranometer UEI DLM2 light meter was used to
measure luminosity intensity at the inlet and mid-
height of the dryer. Digital thermometer EBCHQ (ref:
94196) was used to measure relative humidity and
temperature inlet and outlet from the dryer and at
mid-height of the dryer.
2.2.3.6 Statistical analysis
The data related to environmental measures, DSC,
TGA, and surface area analysis were performed in
triplicate. Statistical analysis was performed using a
one-way ANOVA test complemented by The Tukey
test with a significance level of 95 %. The analysis
was carried out using Statistix ® and Microsoft Excel®
.
3. RESULTS AND DISCUSSION
3.1 Effect of solar drying on pollen grain
morphology
Figure 1 shows the effect of the solar drying process on
the morphology of two characteristic palynomorphs
of bee pollen used in this study, compared to the
effect of a conventional drying process (cabin drying
by forced air convection), evaluated through SEM.
The pollinic structures (A) and (A’) correspond to
fresh bee pollen grains of spiculate and cross-
linked palynomorphs, respectively. Palynomorph
(A) belongs to the Asteraceae family, while (A’)
belongs to the Escallonia pendula family (31). The
structures (B) and (B’) correspond to the same
palynomorphs after solar drying, and the structures
(C) and (C’) correspond to the palynomorphs after
cabin drying. Regarding spiculate palynomorphs
(A, B, C), it can be seen they have a spherical shape
with macropores and hairs that make up the typical
pollinic structure of Asteraceae. Minor changes are
observed in the form of the exine of fresh pollen
grains (A), after solar drying (B), and in the cabin
(C). In this fresh palynomorph (A), it is appreciated
that macropores are deeper than in (B) and (C). It
is important to mention that the exine corresponds
to the outer layer of the bee pollen grain, which
is composed mainly of sporopollenin, resistant to
hydrolytic enzymes and some chemical solvents.
This compound is not currently known in detail, but
it is known that its conformation is mainly given by
compounds similar to lignin, ethers, esters, cross-
linked lipids, and cinnamic acid derivatives (12). In
previous studies of drying, microencapsulation,
and fermentation, it has been observed some
changes in exine occurred at high temperatures
and/or radiation (12, 32–34), where at temperatures
above 136 °C there is the formation of alkanes,
alkylphenols, and alkenes, however, since drying
processes occur at an average temperature close to
50 °C, and there is no greater effect on the exine.
On the other hand, the hairs of the fresh spiculate
palynomorph (A) are thicker and present in greater
quantity than in structures (B) and (C). It can be
5Journal Vitae | https://revistas.udea.edu.co/index.php/vitaeVolume 29 | Number 03 | Article 350572
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
said there are slight erosions on the surface (exine),
where it is possible to observe that the number of
hairs is reduced in size and quantity. In general, no
noticeable damage or swelling is observed in the
pollen structure, which could be assumed to indicate
a visible change between drying treatments. For the
second palynomorph, the characteristic ellipsoidal
shape with a cross-linked surface can be observed
both in fresh pollen (A’), dry pollen by solar drying
(B’), and dry pollen by cabin (C’). Concerning the
surface structure of these pollinic structures, some
slight deformations were observed in the outer layer,
but it is generally possible to state that, in this case,
there was also no damage or swelling in the integral
structure, verifying that there was no noticeable
qualitative difference between drying treatments
on the bee pollen structure. This is consistent with
previous studies (12, 14).
Figure 1. Bee pollen microphotographs A) Fresh, B) Solar-dried, C) Cabin-dried, A’) Pollinic structure type “ellipsoidal cross-linked” for
fresh bee pollen, B’) Pollinic structure type “ellipsoidal cross-linked” after a process of nine hours of solar drying, C’) Pollinic structure
type “ellipsoidal cross-linked” in a cabin dryer.
In addition to the bee pollen effects of the solar
drying, luminosity intensity (Lux), relative humidity
(%), solar dr yer temperature (°C) and room
temperature (°C) were measured in triplicate on two
different dates.
The solar radiation data in Figure 2 was measured
with a solar radiation device, and the comparison
between the radiation and humidity-temperature
stability indoors and outdoors showed that radiation
variance did not affect humidity and temperature
stability. In addition, weather conditions did not
affect samples, and humidity had changed only
during the first three hours, which is consistent with
the above on the preservation of the surface area
structure of bee pollen.
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
said there are slight erosions on the surface (exine),
where it is possible to observe that the number of
hairs is reduced in size and quantity. In general, no
noticeable damage or swelling is observed in the
pollen structure, which could be assumed to indicate
a visible change between drying treatments. For the
second palynomorph, the characteristic ellipsoidal
shape with a cross-linked surface can be observed
both in fresh pollen (A’), dry pollen by solar drying
(B’), and dry pollen by cabin (C’). Concerning the
surface structure of these pollinic structures, some
slight deformations were observed in the outer layer,
but it is generally possible to state that, in this case,
there was also no damage or swelling in the integral
structure, verifying that there was no noticeable
qualitative difference between drying treatments
on the bee pollen structure. This is consistent with
previous studies (12, 14).
Figure 1. Bee pollen microphotographs A) Fresh, B) Solar-dried, C) Cabin-dried, A’) Pollinic structure type “ellipsoidal cross-linked” for
fresh bee pollen, B’) Pollinic structure type “ellipsoidal cross-linked” after a process of nine hours of solar drying, C’) Pollinic structure
type “ellipsoidal cross-linked” in a cabin dryer.
In addition to the bee pollen effects of the solar
drying, luminosity intensity (Lux), relative humidity
(%), solar dr yer temperature (°C) and room
temperature (°C) were measured in triplicate on two
different dates.
The solar radiation data in Figure 2 was measured
with a solar radiation device, and the comparison
between the radiation and humidity-temperature
stability indoors and outdoors showed that radiation
variance did not affect humidity and temperature
stability. In addition, weather conditions did not
affect samples, and humidity had changed only
during the first three hours, which is consistent with
the above on the preservation of the surface area
structure of bee pollen.
6Journal Vitae | https://revistas.udea.edu.co/index.php/vitae Volume 29 | Number 03 | Article 350572Bryan Alberto Castellanos-Paez, Andrés Durán-Jiménez, Carlos Alberto Fuenmayor, Marta Cecilia Quicazán, Carlos Mario Zuluaga-Domínguez
In Figures 3 and 4, while the solar dryer temperature
reached stability at 10 am, humidity indoors the
dryer kept on decreasing until 1 pm. This behavior
shows that at a constant temperature, the relative
humidity will reach equilibrium as expected, and
possibly all solar radiation energy is not used to
reduce the humidity in the air. Also, the maximum
humidity absorption capacity of air changed from
3.0 g water/kg dry air to 5.7 g water/kg dry air. These
values were calculated using the psychrometric chart
by taking the dry bulb temperature, and relative
humidity at 8 and 11 am using Figures 4 and 5
(where an approximately constant temperature
begins inside and outside the solar dryer). Air to
saturation with a relative humidity of 100 % was
assumed for this calculation. These values were
plotted on a psychrometric chart to find the humidity
ratio (specific humidity) in g water/kg dry air. Then,
the adiabatic cooling line was followed (wet bulb
temperature), and the new humidity ratio (specific
humidity) was found where the air was saturated.
The differences were made between the initial and
the final values, and the change was found, which
is the maximum moisture carrying capacity at 8 am
and 11 am reported above.
Figure 2. Variations of solar radiation with time of day for a typical experimental run during solar drying of bee pollen. Different
letters mean significant differences (alpha< 0.05)
Figure 3. Variations of indoor relative humidity in solar dryer and ambient relative humidity with time of day for a typical experimental
run during solar drying of bee pollen.
Different letters mean significant differences (alpha< 0.05)
In Figures 3 and 4, while the solar dryer temperature
reached stability at 10 am, humidity indoors the
dryer kept on decreasing until 1 pm. This behavior
shows that at a constant temperature, the relative
humidity will reach equilibrium as expected, and
possibly all solar radiation energy is not used to
reduce the humidity in the air. Also, the maximum
humidity absorption capacity of air changed from
3.0 g water/kg dry air to 5.7 g water/kg dry air. These
values were calculated using the psychrometric chart
by taking the dry bulb temperature, and relative
humidity at 8 and 11 am using Figures 4 and 5
(where an approximately constant temperature
begins inside and outside the solar dryer). Air to
saturation with a relative humidity of 100 % was
assumed for this calculation. These values were
plotted on a psychrometric chart to find the humidity
ratio (specific humidity) in g water/kg dry air. Then,
the adiabatic cooling line was followed (wet bulb
temperature), and the new humidity ratio (specific
humidity) was found where the air was saturated.
The differences were made between the initial and
the final values, and the change was found, which
is the maximum moisture carrying capacity at 8 am
and 11 am reported above.
Figure 2. Variations of solar radiation with time of day for a typical experimental run during solar drying of bee pollen. Different
letters mean significant differences (alpha< 0.05)
Figure 3. Variations of indoor relative humidity in solar dryer and ambient relative humidity with time of day for a typical experimental
run during solar drying of bee pollen.
Different letters mean significant differences (alpha< 0.05)
7Journal Vitae | https://revistas.udea.edu.co/index.php/vitaeVolume 29 | Number 03 | Article 350572
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
In addition, Figure 5 presents the drying curve. The
moisture content in the solar dryer went from 21,03
% (d.b.) to 6,51 % (d. b.) for 9 hours, and in the cabin
dryer, bee pollen went from 21,01 % (d.b.) to 3,74
% (d.b.) that is equilibrium moisture for the same
period. The curve of the solar dryer showed that
the moisture content remained similar to that of the
cabin dryer during the first hour up to the fourth
hour (in addition to the fact that in this section, the
constant drying rate for solar drying was 0.031 2
*
kg
h m
and for cabin drying was 0.030 2
*
kg
h m
(alpha< 0.05).
After that, the drying rate in a cabin dryer was higher
than solar dryer because the temperature and air
conditions allowed better water removal.
Figure 4. Variations of indoor temperature in solar dryer and ambient temperature with time of day for a typical experimental run
during solar drying of bee pollen.
Different letters mean significant differences (alpha< 0.05)
Figure 5. Moisture content vs drying time curve of the cabin dryer and the solar dryer.
This result is consistent with the information
presented above because the final moisture content
in bee pollen in a solar dryer was higher than cabin
dryer. This could contribute to keep the surface
structure undamaged because the exine was not
completely exposed to radiation that might be
hazardous for surface compounds of bee pollen.
Besides, this moisture content protected the
structure. This result was similar to those reported
by Durán et al. (1) who studied the effect of solar
drying on antioxidant compounds of bee pollen and
showed solar radiation was not harmful to bee pollen
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
In addition, Figure 5 presents the drying curve. The
moisture content in the solar dryer went from 21,03
% (d.b.) to 6,51 % (d. b.) for 9 hours, and in the cabin
dryer, bee pollen went from 21,01 % (d.b.) to 3,74
% (d.b.) that is equilibrium moisture for the same
period. The curve of the solar dryer showed that
the moisture content remained similar to that of the
cabin dryer during the first hour up to the fourth
hour (in addition to the fact that in this section, the
constant drying rate for solar drying was 0.031 2
*
kg
h m
and for cabin drying was 0.030 2
*
kg
h m
(alpha< 0.05).
After that, the drying rate in a cabin dryer was higher
than solar dryer because the temperature and air
conditions allowed better water removal.
Figure 4. Variations of indoor temperature in solar dryer and ambient temperature with time of day for a typical experimental run
during solar drying of bee pollen.
Different letters mean significant differences (alpha< 0.05)
Figure 5. Moisture content vs drying time curve of the cabin dryer and the solar dryer.
This result is consistent with the information
presented above because the final moisture content
in bee pollen in a solar dryer was higher than cabin
dryer. This could contribute to keep the surface
structure undamaged because the exine was not
completely exposed to radiation that might be
hazardous for surface compounds of bee pollen.
Besides, this moisture content protected the
structure. This result was similar to those reported
by Durán et al. (1) who studied the effect of solar
drying on antioxidant compounds of bee pollen and
showed solar radiation was not harmful to bee pollen
8Journal Vitae | https://revistas.udea.edu.co/index.php/vitae Volume 29 | Number 03 | Article 350572Bryan Alberto Castellanos-Paez, Andrés Durán-Jiménez, Carlos Alberto Fuenmayor, Marta Cecilia Quicazán, Carlos Mario Zuluaga-Domínguez
compounds (carotenoids and phenols). This type of
drying is an alternative to traditional dehydration.
In addition, the average solar drying conditions are
also reliable for bee pollen drying because capillarity
and diffusion mass transfer are feasible according
to the drying kinetics data.
Based on these results, employing a less invasive
process in the product, such as solar and conventional
drying, results in a milder alteration in grain
morphology, and the characteristic geometry can
be preserved after these treatments.
3.2 Effect of solar drying on the calorimetric
profile of pollen
The results obtained for DSC and TGA are presented
in Figures 6 and 7, respectively. The thermogram in
Figure 6 shows that there were two endothermal
phase transitions, one at 148 °C (I) and one at 160 °C
(II), for fresh bee pollen. When analyzing this
thermogram, it is possible to observe a first phase
transition (148 °C) which represents a 10 % mass loss
in fresh bee pollen; meanwhile, decreases of 5 % and
6 % were found for cabin and solar dried bee pollen,
respectively. In addition, the second phase transition
(160 °C) was not observable in dried samples. This
indicates that the phase transition corresponding to
peak I in Figure 6 was due to water loss. Zuluaga et al.
(35) performed a DSC analysis on fermented pollen
with Lactic acid bacteria, finding a slight change in
thermal profiles below 140 °C, associated with the loss
of evaporated free water; with this information, it can
be validated that the results are consistent with other
reports. The second phase transition (160 °C) could
be associated with the loss of volatile compounds.
Ahmed et al. (36) and Zuluaga et al. (12) reported that
at temperatures close to 180 °C, the loss of volatile
compounds could occur due to the weakening of the
exine, and at higher temperatures begin formations
of aliphatic compounds and hydrocarbons, therefore
the results obtained are validated.
Figure 6. DSC results for bee pollen.
Figure 7. DTG results for bee pollen.
This would explain why this peak was not visible in
dried bee pollen samples, where there can be a
significant loss of volatile compounds. The energy
required for each of the phase transitions was
obtained through the integration of the area under
the thermogram curve (Figure 6). Fresh bee pollen
had a total value of 381 kJ/kg, while dried bee pollen
had 93.4 kJ/kg pollen and 108.4 kJ/kg in both cabin
and solar, respectively. The quotients between
these energies and the mass fractions of water in
the corresponding bee pollen samples, both fresh
and dry (0.170 g/g and 0.047 g/g, respectively),
had values between 2241 and 2309 kJ/kg of water.
These values were very close to the enthalpy of
water evaporation which is 2257 kJ/kg, according
to Perry et al. (37).
The difference in phase transition temperature
for cabin-dried bee pollen (Figure 6) compared to
fresh and solar-dried could be due to the above-
mentioned exine degradations and/or structural
changes, which could also indicate a possible
change in exine (38). On the other hand, Figure 7
shows the loss of mass for fresh, cabin-dried, and
solar dried bee pollen with respect to temperature,
occurring in two specific stages: the first stage is
presented at 130 °C which corresponds mostly to
the loss of free water, where the mass loss by the
integration of the peaks were 13 %, 6 % and 7 %
for fresh, cabin-dried, and solar dried bee pollen,
respectively. The second stage is observed at 190
°C, corresponding to the loss of mass of volatile
compounds (36) of about 14.5 %, 13.4 %, and 12.2 %
for fresh, cabin-dried, and solar-dried, respectively.
It is also possible to see in Figure 7 that at 200 °C,
there was a cumulative loss of total mass of 29 %
in fresh bee pollen, while this loss is 22 % and 21
% for cabin-dried and solar dried, respectively.
Results found by Sebii et al. (39) and Zuluaga et al.
(12) showed mass losses of 30 % for temperatures
close to 170°C, which were distributed in two stages:
the first between 50 °C and 60 °C, associated with
compounds (carotenoids and phenols). This type of
drying is an alternative to traditional dehydration.
In addition, the average solar drying conditions are
also reliable for bee pollen drying because capillarity
and diffusion mass transfer are feasible according
to the drying kinetics data.
Based on these results, employing a less invasive
process in the product, such as solar and conventional
drying, results in a milder alteration in grain
morphology, and the characteristic geometry can
be preserved after these treatments.
3.2 Effect of solar drying on the calorimetric
profile of pollen
The results obtained for DSC and TGA are presented
in Figures 6 and 7, respectively. The thermogram in
Figure 6 shows that there were two endothermal
phase transitions, one at 148 °C (I) and one at 160 °C
(II), for fresh bee pollen. When analyzing this
thermogram, it is possible to observe a first phase
transition (148 °C) which represents a 10 % mass loss
in fresh bee pollen; meanwhile, decreases of 5 % and
6 % were found for cabin and solar dried bee pollen,
respectively. In addition, the second phase transition
(160 °C) was not observable in dried samples. This
indicates that the phase transition corresponding to
peak I in Figure 6 was due to water loss. Zuluaga et al.
(35) performed a DSC analysis on fermented pollen
with Lactic acid bacteria, finding a slight change in
thermal profiles below 140 °C, associated with the loss
of evaporated free water; with this information, it can
be validated that the results are consistent with other
reports. The second phase transition (160 °C) could
be associated with the loss of volatile compounds.
Ahmed et al. (36) and Zuluaga et al. (12) reported that
at temperatures close to 180 °C, the loss of volatile
compounds could occur due to the weakening of the
exine, and at higher temperatures begin formations
of aliphatic compounds and hydrocarbons, therefore
the results obtained are validated.
Figure 6. DSC results for bee pollen.
Figure 7. DTG results for bee pollen.
This would explain why this peak was not visible in
dried bee pollen samples, where there can be a
significant loss of volatile compounds. The energy
required for each of the phase transitions was
obtained through the integration of the area under
the thermogram curve (Figure 6). Fresh bee pollen
had a total value of 381 kJ/kg, while dried bee pollen
had 93.4 kJ/kg pollen and 108.4 kJ/kg in both cabin
and solar, respectively. The quotients between
these energies and the mass fractions of water in
the corresponding bee pollen samples, both fresh
and dry (0.170 g/g and 0.047 g/g, respectively),
had values between 2241 and 2309 kJ/kg of water.
These values were very close to the enthalpy of
water evaporation which is 2257 kJ/kg, according
to Perry et al. (37).
The difference in phase transition temperature
for cabin-dried bee pollen (Figure 6) compared to
fresh and solar-dried could be due to the above-
mentioned exine degradations and/or structural
changes, which could also indicate a possible
change in exine (38). On the other hand, Figure 7
shows the loss of mass for fresh, cabin-dried, and
solar dried bee pollen with respect to temperature,
occurring in two specific stages: the first stage is
presented at 130 °C which corresponds mostly to
the loss of free water, where the mass loss by the
integration of the peaks were 13 %, 6 % and 7 %
for fresh, cabin-dried, and solar dried bee pollen,
respectively. The second stage is observed at 190
°C, corresponding to the loss of mass of volatile
compounds (36) of about 14.5 %, 13.4 %, and 12.2 %
for fresh, cabin-dried, and solar-dried, respectively.
It is also possible to see in Figure 7 that at 200 °C,
there was a cumulative loss of total mass of 29 %
in fresh bee pollen, while this loss is 22 % and 21
% for cabin-dried and solar dried, respectively.
Results found by Sebii et al. (39) and Zuluaga et al.
(12) showed mass losses of 30 % for temperatures
close to 170°C, which were distributed in two stages:
the first between 50 °C and 60 °C, associated with
9Journal Vitae | https://revistas.udea.edu.co/index.php/vitaeVolume 29 | Number 03 | Article 350572
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
water evaporation, and the second stage between
170 °C and 190 °C, associated with the liberation of
volatile compounds.
When comparing these results with those obtained
by SEM, it is possible to observe that slight changes
in the surface layer of exine in dried bee pollen
samples could be due to reduced moisture, but there
was no damage or swellings in the morphological
structure. Therefore, the behavior of solar drying is
like cabin drying, which implies that the solar drying
process is an adequate and reliable process for
dehydrating bee pollen.
3.3. Surface area analysis
An important aspect of the morphological and
textural characteristics of bee pollen is porosity,
which represents a useful feature for fields such
as microencapsulation, fermentation, and drying
(14, 40, 41) since it can be useful to establish if
the material suffers any structural change when
undergoing different treatments and knowing if
the material has porosity. For both cabin and solar
dried pollen, it may indicate the differences or
similarities between drying treatments; this, in turn,
highlights the importance of morphological analysis
in food because structural integrity may represent
an indirect measure of the effects of different
treatments on the surface structure that could
impact nutritional and microbiological changes. This
study is a pioneer in bee pollen porosity analysis
before and after drying treatments due to the little
information available on the subject.
The result of the surface area analysis is presented
in Fig. 8. The absorption curves show the results of
the volume absorbed for cabin-dried and solar-dried
bee pollen. For values less than a relative pressure of
0.95, it can be observed that the volume absorbed
is zero for bee pollen samples from both cabin and
solar dryers, but for values greater than 0.95 in the
relative pressure, it was obtained an increase in the
absorbed volume that could not be considered as
porosity. In this sense, bee pollen samples did not
show pore size distribution, according to previous
studies, which is obtained through treatments with
zinc oxide and other materials (40, 42), but they did
have deformations and concavities that allowed
mass transfer by capillarity and diffusion. Studies
made by Benavent et al. (43) on the evaluation of
porosity in starch samples subjected to amylolytic
enzymes showed a greater porosity and absorption
of water or oils, indicating that morphology plays
a fundamental role in conditioning processing.
On the other hand, Sozer et al. (44) report that
porosity depends on the cell shape and size,
relative density, and composition-thickness of the
cell wall. In addition, these characteristics establish
the morphology and textural properties of different
foods related to sensory properties.
Figure 8. Measured adsorption isotherm for microscopical dried bee pollen (same isotherm for the two treatments) where a fixed
surface area without porosity is observed.
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
water evaporation, and the second stage between
170 °C and 190 °C, associated with the liberation of
volatile compounds.
When comparing these results with those obtained
by SEM, it is possible to observe that slight changes
in the surface layer of exine in dried bee pollen
samples could be due to reduced moisture, but there
was no damage or swellings in the morphological
structure. Therefore, the behavior of solar drying is
like cabin drying, which implies that the solar drying
process is an adequate and reliable process for
dehydrating bee pollen.
3.3. Surface area analysis
An important aspect of the morphological and
textural characteristics of bee pollen is porosity,
which represents a useful feature for fields such
as microencapsulation, fermentation, and drying
(14, 40, 41) since it can be useful to establish if
the material suffers any structural change when
undergoing different treatments and knowing if
the material has porosity. For both cabin and solar
dried pollen, it may indicate the differences or
similarities between drying treatments; this, in turn,
highlights the importance of morphological analysis
in food because structural integrity may represent
an indirect measure of the effects of different
treatments on the surface structure that could
impact nutritional and microbiological changes. This
study is a pioneer in bee pollen porosity analysis
before and after drying treatments due to the little
information available on the subject.
The result of the surface area analysis is presented
in Fig. 8. The absorption curves show the results of
the volume absorbed for cabin-dried and solar-dried
bee pollen. For values less than a relative pressure of
0.95, it can be observed that the volume absorbed
is zero for bee pollen samples from both cabin and
solar dryers, but for values greater than 0.95 in the
relative pressure, it was obtained an increase in the
absorbed volume that could not be considered as
porosity. In this sense, bee pollen samples did not
show pore size distribution, according to previous
studies, which is obtained through treatments with
zinc oxide and other materials (40, 42), but they did
have deformations and concavities that allowed
mass transfer by capillarity and diffusion. Studies
made by Benavent et al. (43) on the evaluation of
porosity in starch samples subjected to amylolytic
enzymes showed a greater porosity and absorption
of water or oils, indicating that morphology plays
a fundamental role in conditioning processing.
On the other hand, Sozer et al. (44) report that
porosity depends on the cell shape and size,
relative density, and composition-thickness of the
cell wall. In addition, these characteristics establish
the morphology and textural properties of different
foods related to sensory properties.
Figure 8. Measured adsorption isotherm for microscopical dried bee pollen (same isotherm for the two treatments) where a fixed
surface area without porosity is observed.
10Journal Vitae | https://revistas.udea.edu.co/index.php/vitae Volume 29 | Number 03 | Article 350572Bryan Alberto Castellanos-Paez, Andrés Durán-Jiménez, Carlos Alberto Fuenmayor, Marta Cecilia Quicazán, Carlos Mario Zuluaga-Domínguez
Thakur et al. (45) reported that the different
botanical origins of bee pollen affect its physical
and textural properties, where porosity varies
according to the origin and directly affects thermal
stability, so the greater porosity, the less thermal
stability. Knowing these reports, it is possible to
understand the importance of morphology in bee
pollen, necessary to include it as a determining
factor of characterization. These results, together
with those obtained in DSC, DTG, and SEM, make
it possible to establish that there was no damage
to the bee pollen structure when subjected to
solar drying, and the comparison with cabin drying
showed similar behavior and, therefore, strengthens
the use of solar drying as a dehydration alternative
for plant-origin foods.
CONCLUSION
The results obtained in SEM micrographs, DSC-DTG
thermograms, and the adsorption diagram made it
possible to consider that solar drying did not cause
damage or swelling on the bee pollen structure,
then solar drying can be considered appropriate
for dehydration with a similar outcome to cabin
drying because the final moisture content in the
solar dryer was 6.51 % (d.b.) and in cabin dryer,
bee pollen was 3.74 % (d.b.) for 9 hours of drying.
This condition allows the establishment of another
reliable alternative for drying bee pollen intended
for beekeepers, contributing to reducing energy
costs. The energy needed for the endothermal
phase transition for solar-dried bee pollen was
108.4 kJ/kg with a mass loss of 22 % compared
to cabin-dried bee pollen, which was 93.4 kJ/kg
with a mass loss of 21 %, indicating that there was
a similarity between the thermodynamic changes
of the two types of drying. The above results were
coherent with the results of SEM and surface area
analysis, which showed that the decrease in the level
of moisture in bee pollen generated slight surface
changes in the exine without major modifications,
although the change in the transition from an
endothermic phase in dehydrated bee pollen in the
cabin (144 °C) and dehydrated bee pollen in the solar
dryer (148 °C) occurred due to structural changes
associated with weakening of the exine and possible
generation of new structures. In addition to these
considerations, bee pollen did not show porosity
(for characterized samples) because there was no
increase in adsorbed volume during the applied
adsorption treatment demonstrating that the
material did not have structural damage as already
seen in the SEM and DSC analyses. Future research
should focus on monitoring the microbiological
and bioactive behavior, which complement what
is obtained in this research in a way that provides
more judgmental tools that contribute to the use of
this type of drying.
DECLARATION OF CONFLICTS OF INTEREST
The authors declared no potential conflicts of
interest with respect to the research, authorship,
and/or publication of this article.
FUNDING
This research was funded by Universidad Nacional
de Colombia, through the project “Scaling up of a
passive solar dryer prototype in the Cundiboyacense
highland applicable to products of plant origin”
(Hermes Code: 42974)
AUTHORS’ CONTRIBUTIONS
Brian Alberto Castellanos-Paez: Investigation, Formal
analysis, Writing - Original Draft; Andrés Durán-
Jiménez: Investigation, Formal analysis, Writing
- Review & Editing; Carlos Alberto Fuenmayor:
Conceptualization, Resources, Supervision; Carlos
Mario Zuluaga-Domínguez: Funding acquisition,
Project administration, Supervision.
REFERENCES
1. Durán Jiménez A, Quicazán Sierra M. Diseño de un sistema
de secado y separación de impurezas para polen apícola
en Colombia. [Master’s Grade Work]. [Bogotá, Colombia]:
Universidad Nacional de Colombia: 2014. 181-182 p.
2. Pulido Chavarro NA, Díaz Moreno AC. Influencia del proceso de
deshidratación en la calidad fisicoquímica y bioactiva del polen
apícola. [Master’s Grade Work]. [Bogotá, Colombia]: Universidad
Nacional de Colombia: 2013. 77-78 p.
3. Lulin L, Jianzhong L, Cheng J, Xi J, Zhou J, Cen K. Experimental
Study on Solar Drying of Lignite. IEEE. 2010; 1: 714–18. DOI:
https://doi.org/10.1109/ICDMA.2010.286
4. Barajas JP, Martínez T, Rodriguez E. Evaluación del Efecto de la
Temperatura en el Secado de Polen Apícola Procedente de dos
Zonas de Cundinamarca. Dyna [Internet]. 2011 [cited 2022 Oct
11]; 78: 48–57. Available from: https://www.redalyc.org/articulo.
oa?id=49622372005
5. Rabha DK, Muthukumar P. Feasibility Study of the Application of a
Latent Heat Storage in a Solar Dryer for Drying Green Chili. IEEE.
2018; 2: 1–6. DOI: https://doi.org/10.1109/EPETSG.2018.8658770
6. Nguyen VL. Improvement of conventional solar dr ying
system. IEEE. 2017; 1: 690-693. DOI: https://doi.org/10.1109/
ICSSE.2017.8030964
7. Soledad AM, Correa AR. Efecto del tipo de secado sobre las
propiedades sensoriales intrumentales del polen. Universidad
Nacional de Colombia [Internet]. 2015 [cited 2022 Oct 11];
Thakur et al. (45) reported that the different
botanical origins of bee pollen affect its physical
and textural properties, where porosity varies
according to the origin and directly affects thermal
stability, so the greater porosity, the less thermal
stability. Knowing these reports, it is possible to
understand the importance of morphology in bee
pollen, necessary to include it as a determining
factor of characterization. These results, together
with those obtained in DSC, DTG, and SEM, make
it possible to establish that there was no damage
to the bee pollen structure when subjected to
solar drying, and the comparison with cabin drying
showed similar behavior and, therefore, strengthens
the use of solar drying as a dehydration alternative
for plant-origin foods.
CONCLUSION
The results obtained in SEM micrographs, DSC-DTG
thermograms, and the adsorption diagram made it
possible to consider that solar drying did not cause
damage or swelling on the bee pollen structure,
then solar drying can be considered appropriate
for dehydration with a similar outcome to cabin
drying because the final moisture content in the
solar dryer was 6.51 % (d.b.) and in cabin dryer,
bee pollen was 3.74 % (d.b.) for 9 hours of drying.
This condition allows the establishment of another
reliable alternative for drying bee pollen intended
for beekeepers, contributing to reducing energy
costs. The energy needed for the endothermal
phase transition for solar-dried bee pollen was
108.4 kJ/kg with a mass loss of 22 % compared
to cabin-dried bee pollen, which was 93.4 kJ/kg
with a mass loss of 21 %, indicating that there was
a similarity between the thermodynamic changes
of the two types of drying. The above results were
coherent with the results of SEM and surface area
analysis, which showed that the decrease in the level
of moisture in bee pollen generated slight surface
changes in the exine without major modifications,
although the change in the transition from an
endothermic phase in dehydrated bee pollen in the
cabin (144 °C) and dehydrated bee pollen in the solar
dryer (148 °C) occurred due to structural changes
associated with weakening of the exine and possible
generation of new structures. In addition to these
considerations, bee pollen did not show porosity
(for characterized samples) because there was no
increase in adsorbed volume during the applied
adsorption treatment demonstrating that the
material did not have structural damage as already
seen in the SEM and DSC analyses. Future research
should focus on monitoring the microbiological
and bioactive behavior, which complement what
is obtained in this research in a way that provides
more judgmental tools that contribute to the use of
this type of drying.
DECLARATION OF CONFLICTS OF INTEREST
The authors declared no potential conflicts of
interest with respect to the research, authorship,
and/or publication of this article.
FUNDING
This research was funded by Universidad Nacional
de Colombia, through the project “Scaling up of a
passive solar dryer prototype in the Cundiboyacense
highland applicable to products of plant origin”
(Hermes Code: 42974)
AUTHORS’ CONTRIBUTIONS
Brian Alberto Castellanos-Paez: Investigation, Formal
analysis, Writing - Original Draft; Andrés Durán-
Jiménez: Investigation, Formal analysis, Writing
- Review & Editing; Carlos Alberto Fuenmayor:
Conceptualization, Resources, Supervision; Carlos
Mario Zuluaga-Domínguez: Funding acquisition,
Project administration, Supervision.
REFERENCES
1. Durán Jiménez A, Quicazán Sierra M. Diseño de un sistema
de secado y separación de impurezas para polen apícola
en Colombia. [Master’s Grade Work]. [Bogotá, Colombia]:
Universidad Nacional de Colombia: 2014. 181-182 p.
2. Pulido Chavarro NA, Díaz Moreno AC. Influencia del proceso de
deshidratación en la calidad fisicoquímica y bioactiva del polen
apícola. [Master’s Grade Work]. [Bogotá, Colombia]: Universidad
Nacional de Colombia: 2013. 77-78 p.
3. Lulin L, Jianzhong L, Cheng J, Xi J, Zhou J, Cen K. Experimental
Study on Solar Drying of Lignite. IEEE. 2010; 1: 714–18. DOI:
https://doi.org/10.1109/ICDMA.2010.286
4. Barajas JP, Martínez T, Rodriguez E. Evaluación del Efecto de la
Temperatura en el Secado de Polen Apícola Procedente de dos
Zonas de Cundinamarca. Dyna [Internet]. 2011 [cited 2022 Oct
11]; 78: 48–57. Available from: https://www.redalyc.org/articulo.
oa?id=49622372005
5. Rabha DK, Muthukumar P. Feasibility Study of the Application of a
Latent Heat Storage in a Solar Dryer for Drying Green Chili. IEEE.
2018; 2: 1–6. DOI: https://doi.org/10.1109/EPETSG.2018.8658770
6. Nguyen VL. Improvement of conventional solar dr ying
system. IEEE. 2017; 1: 690-693. DOI: https://doi.org/10.1109/
ICSSE.2017.8030964
7. Soledad AM, Correa AR. Efecto del tipo de secado sobre las
propiedades sensoriales intrumentales del polen. Universidad
Nacional de Colombia [Internet]. 2015 [cited 2022 Oct 11];
11Journal Vitae | https://revistas.udea.edu.co/index.php/vitaeVolume 29 | Number 03 | Article 350572
Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen
1: 1-4. Available from: http://investigacion.bogota.unal.edu.
co/fileadmin/recursos/direcciones/investigacion_bogota/
documentos/enid/2015/memorias2015/ingenieria_tecnologias/
efecto_del_tipo_de_secado_sobre_las_propied.pdf
8. Mujumdar AS. Handbook of Industrial Drying [Internet]. Montreal:
McGill University; 1987 [cited 2022 Oct 11]. 958 p. Available from:
https://www.osti.gov/etdeweb/biblio/7177179
9. Zhang Y, Minglong Z, Hong Z, Zhandong Y. Solar drying for
agricultural products in China. IEEE. 2011; 1: 715–719. DOI:
https://doi.org/10.1109/ICAE.2011.5943895
10. Alvarez RT. Secado Óptimo del Polen para su Conservación
y Caracterización, en un Secador Solar en Arequipa. [Grade
Work]. [Arequipa, Perú]: Universidad Nacional de San Agustín:
2014. 1-37 p.
11. Da Silva RS, Lobo J, Rodrigues M, Bruggianesi G, Guimarães
CL. Kinetics drying of silver banana (Musa spp.) in hybrid dryer.
Revista Ciência Agronômica. 2019; 50 (3): 353–360. DOI: https://
doi.org/10.5935/1806-6690.20190042
12. Zuluaga C, Serrato Bermudez J, Quicazán M. Influence of
dr ying-related operations on microbiological, structural
and physicochemical aspects for processing of bee-pollen.
Engineering in Agriculture, Environment and Food. 2018; 11 (2):
57–64. DOI: https://doi.org/10.1016/j.eaef.2018.01.003
13. Omojola A, Olusola O. Effects of drying on the qualities of some
selected Vegetables. International Journal of Engineering and
Technology. 2009; 1 (5): 409–414. DOI: https://doi.org/10.7763/
IJET.2009.V1.77
14. Isik A, Ozdemir M, Doymaz I. Effect of hot air drying on quality
characteristics and physicochemical properties of bee pollen.
Food Science and Technology. 2018; 39 (10): 224-231. DOI:
https://doi.org/10.1590/fst.02818
15. Cano H, Velásquez H, Arango J. Efecto del secado y presecado
mecánico previo al almacenamiento en la calidad del grano de
café (Coffea arabica L.). Revista U.D.C.A Actualidad & Divulgación
Científica. 2018; 21 (2): 439–448. DOI: https://doi.org/10.31910/
rudca.v21.n2.2018.1068
16. Manzano P, Quijano M, Chóez I, Barragán A. Effect of drying
methods on physical and chemical properties of Ilex guayusa
leaves. Revista Facultad Nacional de Agronomía Medellín.
2018; 71 (3): 8617–8622. DOI: https://doi.org/10.15446/rfnam.
v71n3.71667
17. Kayacan S, Sagdic O, Doymaz I. Effects of hot-air and vacuum
drying on drying kinetics, bioactive compounds and color of bee
pollen. Journal of Food Measurement and Characterization. 2018;
12 (2): 1274-1283. DOI: https://doi.org/10.1007/s11694-018-9741-4
18. Abdullah N, Sulaiman F. A Comparison Study on Oven and
Solar Dried Empty Fruit Bunches. Journal of Environment and
Earth Science [Internet]. 2013 [cited 2022 Oct 11]; 3 (2): 145-156.
Available from: https://www.iiste.org/Journals/index.php/JEES/
article/view/4576/4660
19. Sahin S, Sumnu G, Tunaboyu F. Usage of solar-assisted
spouted bed drier in drying of pea. Food and Bioproducts
Processing. 2013; 91 (3): 271–278. DOI: https://doi.org/10.1016/j.
fbp.2012.11.006
20. Bradbear N. La apicultura y los medios de vida sostenibles
[Internet]. Roma: Folleto de la FAO sobre diversificación 1; 2005
[cited 2022 Oct 11]. Available from: http://www.fao.org/3/y5110s/
y5110s00.htm
21. Pierre JP. Apicultura: Conocimiento de la abeja y manejo de la
colmena [Internet]. Madrid: Ediciones Mundi-Prensa; 2007 [cited
2022 Oct 11]. 789 p. Available from: https://books.google.com.
co/books/about/Apicultura_Conocimiento_de_la_abeja_Mane.
html?id=NRnVlm_rp6kC&redir_esc=y
22. Valdéz P. Polen Apícola: Una alternativa de negocio [Internet].
Santiago de Chile: Apicultura Reporte N°1; 2014 [cited 2022 Oct
11]. 8 p. Available from: https://bibliotecadigital.odepa.gob.cl/
handle/20.500.12650/70079
23. Fuenmayor CA, Zuluaga CM, Díaz AC, Quicazán MC, Cosio M,
Mannino S. Evaluation of the physicochemical and functional
properties of Colombian bee pollen. Revista MVZ Córdoba.
2014; 19 (1): 4003–4014. DOI: https://doi.org/10.21897/rmvz.120
24. Soares V, Dos Santos A, Sampaio DF, Araújo E, Castro AL.
Microbiological quality and physicochemical characterization of
Brazilian bee pollen. Journal of Apicultural Research. 2017; 56 (3):
231–238. DOI: https://doi.org/10.1080/00218839.2017.1307715
25. Komosinska Vassev K, Olczyk P, Kaźmierczak J, Mencner L, Olczyk
K. Bee pollen: chemical composition and therapeutic application.
Evidence-Based Complementary and Alternative Medicine. 2015;
1: 1-6. DOI: https://doi.org/10.1155/2015/297425
26. Kieliszek M, Piwowarek K, Kot AM, Błażejak S, Chlebowska-
Śmigiel A, Wolska I. Pollen and bee bread as new health-oriented
products: A review. Trends in Food Science and Technology.
2017; 71:170–80. DOI: https://doi.org/10.1016/j.tifs.2017.10.021.
27. Ipohorski M, Bozzano P. Microscopía electrónica de barrido
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http://aargentinapciencias.org/wp-content/uploads/2018/01/
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DE-BARRIDO-EN-LA-CARACTERIZACION-DE-MATERIALES-
cei63-3-2013-5.pdf
28. Sharma V, Bhardwaj A. Scanning electron microscopy (SEM)
in food quality evaluation. Evaluation Technologies for Food
Quality. 2019; 1: 743-761. DOI: https://doi.org/10.1016/B978-0-
12-814217-2.00029-9
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1: 1-4. Available from: http://investigacion.bogota.unal.edu.
co/fileadmin/recursos/direcciones/investigacion_bogota/
documentos/enid/2015/memorias2015/ingenieria_tecnologias/
efecto_del_tipo_de_secado_sobre_las_propied.pdf
8. Mujumdar AS. Handbook of Industrial Drying [Internet]. Montreal:
McGill University; 1987 [cited 2022 Oct 11]. 958 p. Available from:
https://www.osti.gov/etdeweb/biblio/7177179
9. Zhang Y, Minglong Z, Hong Z, Zhandong Y. Solar drying for
agricultural products in China. IEEE. 2011; 1: 715–719. DOI:
https://doi.org/10.1109/ICAE.2011.5943895
10. Alvarez RT. Secado Óptimo del Polen para su Conservación
y Caracterización, en un Secador Solar en Arequipa. [Grade
Work]. [Arequipa, Perú]: Universidad Nacional de San Agustín:
2014. 1-37 p.
11. Da Silva RS, Lobo J, Rodrigues M, Bruggianesi G, Guimarães
CL. Kinetics drying of silver banana (Musa spp.) in hybrid dryer.
Revista Ciência Agronômica. 2019; 50 (3): 353–360. DOI: https://
doi.org/10.5935/1806-6690.20190042
12. Zuluaga C, Serrato Bermudez J, Quicazán M. Influence of
dr ying-related operations on microbiological, structural
and physicochemical aspects for processing of bee-pollen.
Engineering in Agriculture, Environment and Food. 2018; 11 (2):
57–64. DOI: https://doi.org/10.1016/j.eaef.2018.01.003
13. Omojola A, Olusola O. Effects of drying on the qualities of some
selected Vegetables. International Journal of Engineering and
Technology. 2009; 1 (5): 409–414. DOI: https://doi.org/10.7763/
IJET.2009.V1.77
14. Isik A, Ozdemir M, Doymaz I. Effect of hot air drying on quality
characteristics and physicochemical properties of bee pollen.
Food Science and Technology. 2018; 39 (10): 224-231. DOI:
https://doi.org/10.1590/fst.02818
15. Cano H, Velásquez H, Arango J. Efecto del secado y presecado
mecánico previo al almacenamiento en la calidad del grano de
café (Coffea arabica L.). Revista U.D.C.A Actualidad & Divulgación
Científica. 2018; 21 (2): 439–448. DOI: https://doi.org/10.31910/
rudca.v21.n2.2018.1068
16. Manzano P, Quijano M, Chóez I, Barragán A. Effect of drying
methods on physical and chemical properties of Ilex guayusa
leaves. Revista Facultad Nacional de Agronomía Medellín.
2018; 71 (3): 8617–8622. DOI: https://doi.org/10.15446/rfnam.
v71n3.71667
17. Kayacan S, Sagdic O, Doymaz I. Effects of hot-air and vacuum
drying on drying kinetics, bioactive compounds and color of bee
pollen. Journal of Food Measurement and Characterization. 2018;
12 (2): 1274-1283. DOI: https://doi.org/10.1007/s11694-018-9741-4
18. Abdullah N, Sulaiman F. A Comparison Study on Oven and
Solar Dried Empty Fruit Bunches. Journal of Environment and
Earth Science [Internet]. 2013 [cited 2022 Oct 11]; 3 (2): 145-156.
Available from: https://www.iiste.org/Journals/index.php/JEES/
article/view/4576/4660
19. Sahin S, Sumnu G, Tunaboyu F. Usage of solar-assisted
spouted bed drier in drying of pea. Food and Bioproducts
Processing. 2013; 91 (3): 271–278. DOI: https://doi.org/10.1016/j.
fbp.2012.11.006
20. Bradbear N. La apicultura y los medios de vida sostenibles
[Internet]. Roma: Folleto de la FAO sobre diversificación 1; 2005
[cited 2022 Oct 11]. Available from: http://www.fao.org/3/y5110s/
y5110s00.htm
21. Pierre JP. Apicultura: Conocimiento de la abeja y manejo de la
colmena [Internet]. Madrid: Ediciones Mundi-Prensa; 2007 [cited
2022 Oct 11]. 789 p. Available from: https://books.google.com.
co/books/about/Apicultura_Conocimiento_de_la_abeja_Mane.
html?id=NRnVlm_rp6kC&redir_esc=y
22. Valdéz P. Polen Apícola: Una alternativa de negocio [Internet].
Santiago de Chile: Apicultura Reporte N°1; 2014 [cited 2022 Oct
11]. 8 p. Available from: https://bibliotecadigital.odepa.gob.cl/
handle/20.500.12650/70079
23. Fuenmayor CA, Zuluaga CM, Díaz AC, Quicazán MC, Cosio M,
Mannino S. Evaluation of the physicochemical and functional
properties of Colombian bee pollen. Revista MVZ Córdoba.
2014; 19 (1): 4003–4014. DOI: https://doi.org/10.21897/rmvz.120
24. Soares V, Dos Santos A, Sampaio DF, Araújo E, Castro AL.
Microbiological quality and physicochemical characterization of
Brazilian bee pollen. Journal of Apicultural Research. 2017; 56 (3):
231–238. DOI: https://doi.org/10.1080/00218839.2017.1307715
25. Komosinska Vassev K, Olczyk P, Kaźmierczak J, Mencner L, Olczyk
K. Bee pollen: chemical composition and therapeutic application.
Evidence-Based Complementary and Alternative Medicine. 2015;
1: 1-6. DOI: https://doi.org/10.1155/2015/297425
26. Kieliszek M, Piwowarek K, Kot AM, Błażejak S, Chlebowska-
Śmigiel A, Wolska I. Pollen and bee bread as new health-oriented
products: A review. Trends in Food Science and Technology.
2017; 71:170–80. DOI: https://doi.org/10.1016/j.tifs.2017.10.021.
27. Ipohorski M, Bozzano P. Microscopía electrónica de barrido
en la caracterización de materiales. Ciencia e Investigación
[Internet]. 2013 [cited 2022 Oct 11]; 63 (3): 44-53. Available from:
http://aargentinapciencias.org/wp-content/uploads/2018/01/
RevistasCeI/tomo63-3/5-MICROSCOPIA-ELECTRONICA-
DE-BARRIDO-EN-LA-CARACTERIZACION-DE-MATERIALES-
cei63-3-2013-5.pdf
28. Sharma V, Bhardwaj A. Scanning electron microscopy (SEM)
in food quality evaluation. Evaluation Technologies for Food
Quality. 2019; 1: 743-761. DOI: https://doi.org/10.1016/B978-0-
12-814217-2.00029-9
29. Mettler Toledo, DSC 1 – TGA Star System calorimeter. https://
www.mt.com/es/es/home/products/Laboratory_ Analytics_
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43. Benavent Y, Rosell C. Morphological and physicochemical
characterization of porous starches obtained from different
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of Biological Macromolecules. 2017; 103: 587–595. DOI: https://
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44. Sozer N, Dogan H, Kokini J. Textural Properties and Their
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45. Thakur M, Nanda V. Exploring the physical, functional, thermal,
and textural properties of bee pollen from different botanical
origins of India. Journal of Food Process Engineering. 2018; 43
(1). DOI: https://doi.org/10.1111/jfpe.12935
37. Perry R, Green D. Perry’s Chemical Engineers’ handbook
[Internet]. New York: McGraw-Hill; 2008 [cited 2022 Oct 11].
2700 p. Available from: https://www.accessengineeringlibrary.
com/content/book/9780071422949
38. Fraser WT, Sephton MA, Watson J, Beerling DJ. UV-B absorbing
pigments in spores: Biochemical responses to shade in a high-
latitude birch forest and implications for sporopollenin-based
proxies of past environmental change. Polar Research. 2011; 30:
DOI: https://doi.org/10.3402/polar.v30i0.8312
39. Sebii H, Karra S, Brahim B, Mokni A, Danthine SM. Physico-
Chemical, Surface and Thermal Properties of Date Palm Pollen
as a Novel Nutritive Ingredient. Advances in Food Technology
and Nutritional Science. 2019; 5 (3): 84-91. DOI: https://doi.
org/10.17140/AFTNSOJ-5-160
40. Tzvetkov G, Kaneva N, Spassov T. Room-temperature fabrication
of core-shell nano-ZnO/pollen grain biocomposite for adsorptive
removal of organic dye from water. Applied Surface Science. 2017;
400: 481–491. DOI: https://doi.org/10.1016/j.apsusc.2016.12.225
41. Ma H, Zhang P, Wang J, Xu X, Zhang H. Preparation of a novel rape
pollen shell microencapsulation and its use for protein adsorption
and pH-controlled release. Journal of Microencapsulation. 2014;
31 (7): 667–73. DOI: https://doi.org/10.3109/02652048.2014.91
3723
42. Zhang L, Lin T, Pan X, Wang W, Liu T. Morphology-controlled
synthesis of porous polymer nanospheres for gas absorption and
bioimaging applications. Journal of Materials Chemistry. 2012;
22 (19): 9861–9869. DOI: https://doi.org/10.1039/C2JM30395G
43. Benavent Y, Rosell C. Morphological and physicochemical
characterization of porous starches obtained from different
botanical sources and amylolytic enzymes. International Journal
of Biological Macromolecules. 2017; 103: 587–595. DOI: https://
doi.org/10.1016/j.ijbiomac.2017.05.089
44. Sozer N, Dogan H, Kokini J. Textural Properties and Their
Correlation to Cell Structure in Porous Food Materials. Journal
of Agricultural and Food Chemistry. 2011; 59 (5): 1498–1507. DOI:
https://doi.org/10.1021/jf103766x
45. Thakur M, Nanda V. Exploring the physical, functional, thermal,
and textural properties of bee pollen from different botanical
origins of India. Journal of Food Process Engineering. 2018; 43
(1). DOI: https://doi.org/10.1111/jfpe.12935