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TECNOCIENCIACHIHUAHUA, Vol. XVI (3) e 1023 (2022)
https://vocero.uach.mx/index.php/tecnociencia
ISSN-e: 2683-3360
Artículo Científico
Valorization of oil industry wastes: Extraction of
phenolic compounds from different sunflower hull
fractions (Helianthus annuus L.)
Revalorización de residuo de la industria aceitera:
Extracción de compuestos fenólicos de distintas fracciones de cáscara
de girasol (Helianthus annuus L.)
*Correspondencia: Correo electrónico: mariamarcelarodriguez@hotmail.com (Marcela Rodríguez)
DOI: https://doi.org/10.54167/tch.v16i3.1023
Recibido: 16 de agosto de 2022; Aceptado: 18 de octubre de 2022
Publicado por la Universidad Autónoma de Chihuahua, a través de la Dirección de Investigación y Posgrado
Abstract
The recovery of antioxidant compounds present in sunflower hulls, a waste byproduct of the oil
extraction process, can be of industrial and environmental interest. The objective of the present
work was to determine different operating conditions for the extraction of phenolic compounds
from hulls oil sunflower seeds, using water at 90 °C and mechanical agitation. To select the
experimental conditions, the hulls of a black hull sunflower hybrid (SPS3120) were analyzed, five
particle sizes (>0.84, 0.84 to 0.42, 0.42 to 0.25, 0.25 to 0.149, <0.149 mm), three pH values (5, 7 and 9)
and samples with and without oil were evaluated. The selected conditions (pH 9, fractions of
particle size ≤0.25 mm- approximately 24 % of the hull, with a prior removal of the oil) were also
applied to other three black-oil hybrids (SyN3840, SyN3950, DK4065) and two striped sunflower
hybrids (CF201, PAN7077), evaluating the total phenol content and total flavonoid content in the
fractions of particle size ≤0.25 and >0.25 mm. By processing approximately 23-24 % of the
sunflower hull (≤0.25 mm particle-size fraction), it was possible to obtain a minimum of 59 and
62% of total phenols and total flavonoids of the total hull, respectively, under the selected
conditions.
Keywords: sunflower hulls, phenolic compounds, particle size, oil, pH.
Daiana Fanesi1, Susana Nolasco1,2 y Marcela Rodríguez1,3*
1 National University of the Center of the Province of Buenos, Faculty of Engineering, TECSE, Olavarria,
Buenos Aires, Argentina.
2 CIC – Group of Scientific Research of Buenos Aires Province, La Plata, Buenos Aires, Argentina.
3 CONICET, Tandil, Buenos Aires, Argentina.
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Resumen
La obtención de compuestos antioxidantes presentes en la cáscara de girasol, residuo del proceso
de extracción de aceite, puede ser de interés industrial y ambiental. El objetivo del presente trabajo
fue determinar diferentes condiciones de proceso para la extracción de compuestos fenólicos de la
cáscara de híbridos de girasol, empleando agua a 90 °C y agitación mecánica. Para la selección de
las condiciones experimentales, las cáscaras de un híbrido de girasol de cáscara negra (SPS3120)
fueron analizadas, cinco dimensiones de partículas (>0.84; 0.84 a 0.42; 0.42 a 0.25; 0.25 a 0.149 y
<0.149 mm), tres valores de pH (5, 7 y 9) y muestras con y sin aceite. Las condiciones seleccionadas
(pH 9, fracciones de partículas de tamaño ≤0.25 mm- aproximadamente el 24 % de la cáscara,
previa eliminación del aceite de las mismas) fueron también aplicadas a otros tres híbridos de
cáscara negra (SyN3840, SyN3950, DK4065) y dos híbridos de cáscara estríada (CF201, PAN7077),
evaluando el contenido de fenoles totales y flavonoides en las fracciones de partículas ≤0.25 mm y
>0.25mm. Procesando aproximadamente el 23-24 % de la cáscara de girasol (fracción de partículas
≤0.25 mm) se logró obtener como mínimo el 59 y el 62 % de los fenoles totales y flavonoides del
total de la cáscara, respectivamente, en las condiciones operativas aplicadas.
Palabras clave: cáscaras de girasol, compuestos fenólicos, tamaño de partícula, aceite, pH.
1. Introduction
The growing demand for processed foods has led as a result to a substantial increase in
solid wastes (such as leaves, skins, seeds, pits, stems, pulps, pressed cakes, pomace and other
lignocellulosic fractions), generating great economic and environmental challenges to food
processing plants (Baiano et al., 2014; Angiolillo et al., 2015; Vats, 2017). Baiano (2014) and
Angiolillo et al. (2015) have reported about the large potential of these wastes as sources of
bioactive compounds (alkaloids, anthocyanins, phytosterols, carotenoids, stilbenes, lignans,
coumarins, and mainly polyphenols) with applications in the food industry and for manufacturing
pharmaceutical products and cosmetic formulations. Thus, their recovery represents a direct and
positive economic and environmental impact for the agri-food sector, adding value by optimizing
the use of natural resources with minimum food waste generation (Carciochi et al., 2017).
Phenolics compounds are capable of capturing free radicals, donate hydrogen atoms or electrons,
or quelate metallic cations, and thus inhibit oxidation. Within this group, polyphenols, which
include flavonoids, tannins and phenolic acids, are widely distributed in foods of vegetable origin
and represent the majority of the antioxidants present in our diet (Hayat et al., 2009). Further, a
number of studies have evaluated phenolic compounds (polyphenols) due to their beneficial effects
against chronic and acute medical conditions such as cancer, heart and inflammatory diseases
(Balasundram et al., 2006; Taha et al., 2012; Baiano et al., 2014).
The phenolic content of foods depends on the characteristics of the raw material related to intrinsic
(genus, species, cultivar) and extrinsic factors (agronomic, environmental, handling and storage
conditions) (Balasundram et al., 2006). The quality of the polyphenolic extracts, in terms of
antioxidant activity, will also depend both on the chemical structure of its phenolic components
and on the extraction method (Nkhili et al., 2009; Rodríguez et al., 2019). Therefore, the selection of
the appropriate conditions for extraction and the influence of the type of hybrid studied should be
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analyzed with great interest (Hayat et al., 2009). Solid-liquid extraction by solvent is the most
commonly used technique to obtain phenolic compounds, using water or solvents such as ethanol,
methanol, acetone or ethyl acetate, either concentrated or diluted in aqueous mixtures to reach the
polarity of the phenolic compound (Oroian et al., 2015). The structural variety of antioxidant
compounds is so wide that there is no single experimental condition that allows to extract all
phenolic compounds (Rodríguez et al., 2019). Thus in the literature the extraction procedures vary a
lot, and include conditions ranging from room temperature to boiling temperature or reflux, as
well as different processing times, various solvents and concentrations, varied sample to solvent
rations, pH, particle sizes and number of extraction steps, which directly affect the extraction
efficiency (Nkhili et al., 2009; Oroian et al., 2015). As a result, for each vegetable matrix, it is
necessary to select the experimental conditions that allow to maximize the yield and antioxidant
activity of the phenolic extracts, and at the same time, minimize the environmental impact (Baiano
et al., 2014).
Oilseed sunflower seeds consist mainly of the kernel, where the oil is synthesized, and the hull
which represents 17 to 31 % d.b. of the seed (De Figueiredo et al., 2015; Menzel et al., 2019). Prior to
oil extraction, the sunflower seeds are partially dehulled, until reaching a 10-12 % range of residual
hull (De Figueiredo et al., 2011), producing an important amount of residue of low specific weight
(approx. 0.1 ton (m3)-1). Several authors have examined sunflower hulls, reporting that they contain
between 0.7-5.4 % of total phenols present in the seed, with chlorogenic acid being the main
component (80 % of phenolic compounds) (Pedrosa et al., 2000; Weisz et al., 2009; Szydłowska-
Czerniak et al., 2011). Different studies have been conducted to determine the operating conditions
for the extraction of phenolic compounds from sunflower hulls. De Leonardis et al. (2005)
evaluated different solvents at different pH, while Szydłowska-Czerniak et al. (2011) analyzed the
effect of the polarity of the solvent, temperature and extraction time on the total phenolic content of
extracts obtained from sunflower hulls, before and after an enzymatic treatment of the hulls,
finding that the total phenolic content increased linearly with extraction temperature and the
polarity of the solvent. Taha et al. (2012) studied the optimization of the extraction of a phenolic
extract from sunflower hulls by analyzing the variables type of solvent, solvent:water ratio and
hull:solvent ratio. Zoumpoulakis et al. (2017) analyzed the ultrasound- and microwave-assisted
extraction, considering as independent variables the nature of the solvent (methanol, aqueous
methanol), solvent volume, temperature and operation time. Rodríguez et al. (2019) examined the
variables time and temperature for the microwave-assisted extraction (600 W) of phenolic
compounds from sunflower hulls using water as solvent. None of these studies analyzed the effect
of the particle size. In this respect, Menzel et al. (2019) evaluated the milling process of hulls from
snack sunflower using two sieves (<0.6 mm and <0.2 mm) and up to three milling steps. They were
able to mill about 90 % of the raw material to a size <0.6 mm in two milling stages (with a sieving
step prior to the second milling, including in this second stage the particles >0.6 mm), thus
increasing by approximately 17 % the phenolic extraction, compared to a single-stage milling.
Sunflower hulls also contain about 3-9 % d.b. of lipids, a part of which is wax (Cancalon, 1971;
Rodriguez et al., 2017). No studies were found that analyzed the effect of the prior oil extraction
from the hull on the phenolic yield. Taking into account this background, the objective of the
present work was to determine different operating conditions (particle size, pH, absence/presence
of oil) for the extraction of phenolic compounds from hulls oil sunflower seeds, using water at
90 °C and mechanical agitation.
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2. Materials and methods
2.1 Materials
Hulls of four black-hulls sunflower hybrid were evaluated: SPS3120 (Syngenta, 23.3 % d.b.
of hull, hull moisture 12.4 % d.b., oil content of the hull 6.4 % d.b.) SyN3840 (Syngenta, 21.3 % d.b.
of hull, moisture 11.7 % d.b., oil content of the hull 9.45 % d.b.), SyN3950 (Syngenta, 24.8 % of hull,
moisture 9.5 % d.b., oil content of the hull 4.60 % d.b.) and DK4065 (Syngenta, 22.4 % of hull,
moisture 12.1 % d.b., oil content of the hull 8.46 % d.b.). Also, hulls of two striped sunflower
hybrids, CF201 (Advanta, 21.0 % d.b. of hull, hull moisture 12.1 % d.b., oil content of the hull 7.73%
d.b.) and PAN7077 (Pannar, 21.4 % d.b. of hull, hull moisture 11.1 % d.b., oil content of the hull
5.08 % d.b.), were analyzed. All the sunflower hybrids were grown in Balcarce (37°45´S, 58°18´W),
province of Buenos (Argentina). Gallic acid and catechin were purchased from Sigma Chemical Co.
(St Louis, MO, USA).
2.2 Obtention of hulls fractions
The hulls of all sunflower hybrids were obtained by mechanical dehulling of the seeds (the
grains were previously cleaned by manually removing the foreign matter) in a centrifugal dehuller
with a peripheral speed of 38.8 m/s (De Figueiredo et al., 2015). The particle size analysis was
performed by grinding (Ultracomb MO-8100 grinder, China, 20 pulses) and then sieving the
samples considering five different particle sizes (>0.84, 0.84 to 0.42, 0.42 to 0.25, 0.25 to 0.149 and
<0.149 mm). The material retained in each sieve (ASTM, Argentina) was weighed, calculating the
percentage of each fraction. On the other hand, the % hulls of each hybrid (item 2.1) was
determined by manual shelling of 10 g of whole seeds. The hulls and kernel obtained were dried in
a forced air circulation oven (Dryinghorn DHG-9123A, China) for 3 hours at 130 °C and then
weighed. The test was carried out in duplicate, and the results were determined as the ratio
between the weight of the hulls and the total weight of the kernels and hulls, expressed as a
percentage.
2.3 Selection of the conditions for the solid-liquid extraction of phenolic
compounds
For the selection of the experimental conditions, hulls of a traditional hybrid of black-hulls
sunflower (SPS3120) were used. The extractions were carried out with 2 g of hulls of hybrid
SPS3120 by mechanical agitation for 2.65 h, using distilled water at 90 °C as solvent, which were
the optimum conditions found by Szydłowska-Czerniak et al., (2011) for the extraction of phenolic
compounds from sunflower hulls, with a sample to solvent ratio of 1:20 (Rodríguez et al., 2019).
The phenolic extracts were centrifuged (15 min at 3200 g; Thermo Fisher Scientific, Sorvall Legend
X1, Germany) and filtered (quantitative filter paper, black ribbon, pore size 28 μm, Brazil). The
filtrate was frozen (-18 °C) and later freeze-dried (-50 °C, 26 Pa, 12 h) (Boyikang Laboratory
Instruments Inc FD-1A-50, China) to constant weight (dry extracted product).
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2.3.1 Extraction of phenolic compounds by fraction hulls: The extractions of
phenolic compounds were carried out from 2 g of hulls corresponding to each of the five particle
sizes analyzed (>0.84, 0.84 to 0.42, 0.42 to 0.25, 0.25 to 0.149 and <0.149 mm). The assay was
performed in triplicate.
2.3.2 Extraction of phenolic compounds by variation of pH: Using the
selected particle size according to the highest total phenolic content, the influence of pH was
evaluated, using 0.2 M solutions of NaH2PO4.2H2O and Na2HPO4.12H2O to reach pH values of 5,
7 and 9 (De Leonardis et al., 2005). The pH values of the solutions were confirmed with a pH-
meter. The assay was performed in triplicate.
2.3.3 Extraction of phenolic compounds in the presence/absence of oil:
Subsequently, using all the selected conditions (particle sizes, pH), the effect of the defatting was
then analyzed, after the oil extraction in a Soxhlet apparatus for 6 h using n-hexane as solvent The
assay was performed in triplicate.
2.4 Solid-liquid extraction of phenolic compounds from hulls of sunflower
hybrids
After selecting the variables of particle size, pH and presence/absence of oil, the extraction
of phenolic compounds was carried out using water at 90 °C, by mechanical agitation for 2.65 h,
with a sample to solvent ratio of 1:20, from hulls of the three types of black-oil sunflower hybrids
and two striped sunflower hybrids. The extracted product, freeze-dried and weighed, was
characterized in terms of total phenols and total flavonoids.
2.4.1 Determination of total phenols: The effect of the variables of the extraction
process (particle size, pH and presence/absence of oil) was evaluated by determining the total
phenol content in the obtained extracts using the Folin-Ciocalteu colorimetric method (Rodríguez
et al., 2019). The content of total phenols in the hulls of the hybrids of sunflower of black hull and
striped hull was evaluated by this technique. The results were expressed as mg of gallic acid
equivalent (GAE) per 100 g of hull fraction and of hulls (d.b.).
2.4.2 Determination of total flavonoids: The total flavonoid content was
determined by the aluminum chloride method in a basic medium, according to the
spectrophotometric technique proposed by Molina-Quijada et al. (2010). The results were expressed
as mg of catechin equivalent (CE) per 100 g of hull fraction and of hulls (d.b.).
2.5 Statistical analysis
The results were analyzed by ANOVA, and Tukey’s test was used for comparing the
means. The statistical analysis was performed with a confidence level of 95 % using the InfoStat
software (Di Rienzo et al. 2014). All the tests were carried out in triplicate.
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3. Results and Discussion
Table 1 presents the total phenol content of each hull fraction obtained for the hybrid
black-hulls sunflower SPS3120. ANOVA analysis allowed to determine statistically significant
differences (p≤0.0001) of total phenol content for the analyzed hull fractions. In general, the total
phenol content increased significantly with decreasing particle size, within a range of 389.7 and
1646.2 mg GAE 100-1 g hull fraction (d.b.). The two smaller size fractions (0.25-0.149 mm and <0.149
mm) were significantly different from the rest of the fractions and between them, presenting a total
phenol concentration that was at least double or triple, respectively, that of the rest. Considering
the total phenols extracted from the total sunflower hulls (adding up the fractions, with the content
expressed as mg GAE 100-1 g hulls d.b.), approximately 51 % of the total phenols obtained from the
total hulls was found in the fractions ≤0.25 mm. It is worth noting that these two fractions
comprised approximately 24 % of the hull, which in an industrial process would represent a lower
solvent consumption, smaller machines or larger production. Therefore, a particle size smaller than
or equal to 0.25 mm (0.25-0.149 mm and <0.149 mm) was selected for this study.
The process was carried out with a solvent (water) that does not pose any health risk, with easy
and flexible handling, and whose efficiency in the extraction of phenolic compounds at 90 °C has
been proven by different authors (Paladino, 2008; Szydlowska-Czerniak et al., 2011). The obtained
results could be explained by the increase in the interfacial area as the particle size decreased,
facilitating the mass transfer and a more efficient solvent-substrate access. The results also suggest
the possibility of a non-homogeneous distribution of the phenolic compounds in the structure of
the hull, with a larger presence in areas that can break more easily. A similar tendency can be
observed when analyzing the data reported by Menzel et al. (2019), who evaluated the milling
process of hulls from snack sunflowers using two sieves (<0.6 mm and <0.2 mm) and up to three
Variables
Levels
Hull yield
(%)
Total phenols
(mg GAE.100-1 g
hull fraction d.b.)*
Average of total
phenols extracted
(mg GAE.100-1 g
hulls d.b.)
Particle size
(mm)
>0.84
7.5 ± 1.2
413.4 ± 17.7a
31.0
0.84-0.42
35.4 ± 0.6
389.7 ± 7.1a
138.0
0.42-0.25
33.3 ± 1.5
518.3 ± 19.4b
172.6
0.25-0.149
13.5 ± 1.0
1387.0 ± 6.2c
187.2
<0.149
10.3 ± 1.1
1646.2 ± 38.9d
169.6
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milling stages. They found that the particles <0.6 mm obtained in the first milling fraction
presented a total phenolic content 88 % higher than that of the particles obtained after milling the
particles >0.6 mm again, even though they did not report on the size distribution of this second
fraction of particles <0.6 mm.
Table 2 shows the total phenol content for the hull fraction of particle size ≤0.25 mm of hybrid
SPS3120, considering the operating variables pH and presence/absence of oil.
Table 2. Selection of the variables pH and presence/absence of oil for the solid-liquid extraction of phenolic
compounds from sunflower hulls (hybrid black-hull SPS3120).
Tabla 2. Selección de las variables pH y presencia/ausencia de aceite para la extracción sólido-líquido de
compuestos fenólicos de cáscaras de girasol (híbrido de cáscara negra SPS3120).
Variables
Levels
Total phenols
(mg GAE.100-1 g hull fraction d.b.)*
pH**
5
1219.8 ± 51.2a
7
1422.0 ± 44.3b
9
1730.9 ± 38.9c
Oil***
W/O
2091.9 ± 48.3a#
O
1907.2 ± 42.8a#
*Different letters indicate significant differences (p≤0.05) between the values of total phenols obtained for each
pH level or for the absence/presence of oil;
**Fraction of particle size ≤0.25 mm;
***pH 9, #mg GAE.100-1 g hull fraction without oil d.b. W/O, hulls without oil; O, hulls with oil
The increase in pH allowed to extract a significantly higher (p≤0.0034) amount of total phenols,
obtaining a maximum of 1730.9 mg GAE 100-1 g hull fraction (d.b) of size ≤0.25 mm (equivalent to
approximately 412 mg GAE/100 g of hulls d.b.). De Leonardis et al. (2005) observed a similar
tendency when they studied the influence of pH (5, 7 and 9) on the extraction with water at a lower
temperature (25 ºC) than used in this work. It is worth noting that the pH increase also results in
extracts with higher protein content, which could require a later stage of purification. However,
different authors (Rawel et al., 2005; Guimarães Drummond e Silva et al., 2017) have reported on
the advantages of the association of proteins and phenolic compounds as potential emulsifiers with
antioxidant activity.
The effect of the present/absence of oil was evaluated for the operating conditions sample:solvent
ratio of 1:20, particle size ≤0.25 mm and pH 9. The prior removal of the oil from the hulls allowed
to increase the extraction yield of total phenols from 1907.2 to 2091.9 mg GAE 100-1 g hull fraction.
Although from a statistical point of view the increase was not significant, it must be pointed out
that the removed oil is another byproduct of this waste from the oil industry. The oil obtained from
the sunflower hulls is a potential source of waxes for the pharmaceutical and cosmetic industry,
the production of biodegradable films, and foods, among other applications (Carelli et al., 2002).
The wax content of the sunflower hybrids used in the present study was determined, obtaining
values in a range between 0.64 and 2.08 g wax 100-1 g hulls d. b. (Rodríguez et al., 2017). Different
studies have shown the feasibility of using sunflower waxes as gelling agents, even at low
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concentrations, for obtaining organogels, replacing saturated and trans fatty acids of the solid
phase in the formulation of products such as margarines (Hwang et al., 2015).
Thus the values selected as the most adequate for the analyzed variables for the extraction of
phenolic compounds were: fraction of particle size ≤ 0.25 mm (which comprises 24% of the hull),
pH 9, with a prior removal of the oil of the hull.
3.1 Extraction of phenolic compounds from sunflower hulls under the selected
conditions
3.1.1 Black Hulls Sunflower Hybrids
Table 3 presents the amount of phenolic compounds (total phenolic and total flavonoids)
extracted from each hull fraction of the three studied sunflower hybrids. Based on the percentage
of each fraction, the concentration of phenolic compounds in relation to total hulls was also
calculated.
The smaller particles (≤0.25 mm) represented a low percentage (approximately between 23-24 %)
compared to the larger particles, in agreement with the methodological conditions. The total
phenol content determined for the fractions of smaller particle size (≤0.25 mm) varied between
504.2 and 1291.9 mg GAE 100-1 g hull fraction (d.b.), with the content for each hybrid being
significantly higher (p≤0.05) than that found for the larger size fractions (in the range of 75.9 and
194.8 mg GAE 100-1 g hull fraction (d.b.)). The total flavonoid content varied between 423.5 and
830.2 CE 100-1 g hull fraction (d.b.) for particle sizes ≤0.25 mm, and between 66.6 and 75.2 CE 100-1 g
hull fraction (d.b.) for particle sizes >0.25 mm, showing that the total flavonoid content was
significantly higher (p≤0.05) when the extractions were carried out with particles ≤0.25 mm.
Table 3. Phenolic compounds extracted from the hull of different sunflower hybrids (black-hull) grown in
Argentina (solid-liquid extraction, mechanical agitation).
Tabla 3. Extracción de compuestos fenólicos de cáscaras de girasol de diferentes híbridos (cáscara negra)
cultivados en Argentina (extracción sólido-líquido, agitación mecánica).
Hybrids
Particle
size (mm)
Hull yield
(%)
Total
phenols
Total
flavonoids
Total
phenols
Total
flavonoids
*Hull fraction
**Hulls
(calculated)
SyN3840
≤0.25
23.7
845.7 ± 26.3b
627.5 ± 3.8b
200.4
148.7
>0.25
76.3
181.6 ± 0.5a
66.6 ± 4.6a
138.6
50.8
SyN3950
≤0.25
23.2
1291.9 ± 76.5b
830.2 ± 94.9b
299.7
192.6
>0.25
76.8
194.8 ± 15.6a
74.7 ± 4.2a
149.6
57.4
DK4065
≤0.25
22.8
504.2 ± 72.3b
423.5 ± 87.2b
115.0
96.6
>0.25
77.2
75.9 ± 13.2a
75.2 ± 21.6a
58.6
58.1
d.b., dry basis
Different letters indicate significant differences (p≤0.05) between particles sizes of each hybrid
*Total phenols (mg GAE.100-1 g hull fraction d.b.), *Total flavonoids (mg CE.100-1 g hull fraction d.b.)
**Total phenols (mg GAE.100-1 g hulls d.b.), **Total flavonoids (mg CE.100-1 g hulls d.b.)
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By comparing the fractions of smaller size (particles ≤0.25 mm), a significant difference was
detected between the hybrids, both in total phenolic content and total flavonoid content (p≤0.0025
and p≤0.0276, respectively). As for total phenols, all the hybrids differed, with the fraction of
hybrid SyN3950 presenting the highest value, followed by SyN3840 and DK4065, in decreasing
order. This fraction of SyN3950 was also characterized by a higher total flavonoid yield, but
without being significantly different from SyN3840 (Fig. 1A). On the other hand, in the fractions of
larger particle size (>0.25mm), ANOVA only revealed significant differences between hybrids for
total phenolic content (p≤0.0037), with hybrid DK4065 exhibiting the lowest value. The other two
hybrids were not significantly different (Fig. 1B).
Fig. 1. Total phenols and total flavonoids in sunflower hulls fractions (black-hull). A: Size ≤0.25 mm, B: Size:
>0.25mm.
Fig. 1. Fenoles totales y flavonoides totales en fracciones de cáscaras de girasol (cáscara negra). A: Tamaño
≤0.25 mm, B: Tamaño: >0.25mm.
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Although the statistical analysis allowed finding significant differences between the hybrids
studied. It is worth noting that Rodriguez et al. (2019), when evaluating the total phenol and total
flavonoid contents in sunflower hulls using a microwave-assisted extraction process (water at 90
ºC, 10 min, 600 W, sample:solvent ratio of 1:20, particle size of the hull ≤0.42 mm), did not observe
significant differences between these three hybrids grown in two districts in the Buenos Aires
province, Argentina.
By processing the fractions of particle size ≤0.25 mm by the selected method, it was possible to
obtain approximately 59 %, 67 % and 66 % of total phenols from the hulls of hybrids SyN3840,
SyN3950 and DK4065, respectively, and approximately 75 %, 77 % and 62 % of total flavonoids,
respectively (values calculated based on the last 2 columns of Table 3). Therefore, by processing
only between 22.8 and 23.7 % of the hull of these hybrids (particle size 0.25mm) by mechanical
extraction (agitation), a minimum of 59 % of total phenols and 62 % of total flavonoids was
extracted, in relation to total hulls, with a maximum yield of 67 % and 77 %, respectively.
3.1.2 Striped Hulls Sunflower Hybrids
Two striped-hull sunflower hybrids, CF201 and PAN7077 were also evaluated. While hybrid
CF201 exhibited similar tendencies to those observed for the black oil hybrids (Table 4), although
with lower relative yield percentages (53 % and 66 % for total phenols and total flavonoids,
respectively, obtained from the fraction of particle size ≤0.25 mm), the hybrid PAN7077 did not
present differences in the concentration of total phenols between the fractions, indicating that only
30 % of total phenols were extracted from the smaller size fraction, while the larger proportion of
total flavonoids was the same (60 % of total flavonoids of the hull). These results would suggest a
differential behavior of the striped sunflower hybrids, with further studies being necessary to
examine a larger number of hybrids and evaluate possible relations with morphological differences
of the hull (Lindström et al., 2000).
Table 4. Phenolic compounds extracted from hulls of two sunflower hybrids (striped hull) grown in Balcarce,
Argentina (solid-liquid extraction, mechanical agitation).
Tabla 4. Extracción de compuestos fenólicos de cáscaras de dos híbridos de girasol (cáscara estriada)
cultivados en Balcarce, Argentina (extracción sólido-líquido, agitación mecánica).
Property
Hybrid CF201
Hybrid PAN7077
≤0.25
>0.25
≤0.25
>0.25
Hull yield (%)
30.8
69.2
24.5
75.5
Total phenols
*Hull fraction
437.7 ± 17.8b
171.9 ± 40.6a
230.6 ± 24.5a
176.8 ± 9.1a
Total flavonoids
436.6 ± 48.9b
99.1 ± 0.1a
369.5 ± 2.1b
78.6 ± 2.1a
Total phenols
**Hulls
134.8
119.0
56.5
133.5
Total flavonoids
134.5
68.6
90.5
59.3
Different letters indicate significant differences (p≤0.05) between particles sizes of each hybrid;
*Total phenols (mg GAE.100-1 g hull fraction d.b.),*Total flavonoids (mg GAE.100-1 g hull fraction d.b.);
**Total phenols (mg GAE.100-1 g hulls d.b),**Total flavonoids (mg CE.100-1 g hulls d.b.);
d.b., dry basis
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Hemery et al. (2011) and Laguna et al. (2018) reported that the ultrafine milling with electrostatic
sorting or turbo separation are new eco-friendly and energy-efficient technologies that are being
studied for the concentration of components of different agricultural resources, such as proteins,
cellulose, lignin and polyphenols. Laguna et al. (2018) reported that with an adequate combination
of these technologies it is possible to recover fractions rich in proteins and phenolic compounds
from residual meals of sunflower and canola oil extraction processes. Proteins were separated
together with the phenolic compounds, and thus dry fractionation constitutes a pre-purification
process, prior to solid-liquid extraction. Taking into account the results obtained in the present
work, further studies are desirable to determine the potentiality of applying these technologies to
the extraction of phenolic compounds from sunflower hulls with distinguishing features.
The type and amount of phenolic compounds present in the sunflower hulls and in the extracts
obtained from the hulls, as well as the antioxidant properties of the extracts, have been reported by
various authors (De Leonardis et al., 2005; Weisz et al., 2009; Szydlowska-Czerniak et al., 2011; Taha
et al., 2012; Zoumpoulakis et al., 2017; Rodríguez et al., 2019). Taha et al. (2012) also found that
phenolic extracts of sunflower hulls exhibited antimicrobial activity at different levels against
different pathogenic bacteria, as well as anti-carcinogenic activity, which differed between the cell
line carcinomas. Rodríguez et al. (2019) determined and compared the antioxidant activity of
extracts of phenolic compounds (microwave-assisted extraction with water as solvent, 90 °C) from
hulls of the sunflower hybrids studied in the present work, grown in two districts in the Buenos
Aires province, Argentina. Further studies are necessary to determine the impact of the dry
fractionation proposed in this work.
4. Conclusions
The extraction of phenolic compounds from hulls of sunflower hybrids by solid-liquid
extraction using water at 90 °C, mechanical agitation for 2.65 h and a sample:solvent ratio of 1:20
was evaluated, selecting as the most adequate experimental conditions a particle size ≤0.25 mm,
pH 9, with prior removal of the oil from the hulls. Between 23-24 % of hulls of particle size ≤0.25
mm and between 76-77 % of size >0.25 mm were obtained by grinding the hulls of the hybrids
under study. It was possible to extract between 59-67 % of total phenols and 62-77 % of total
flavonoids from the fraction of smaller size, with respect to total hulls, observing differences in
behavior between the hybrids. The present work shows the advantages of combining the grinding
process with an adequate classification of the obtained product, which would allow to reduce the
material to be extracted, obtaining a good yield of phenolic compounds for their potential
application in the formulation of functional foods, or in the pharmaceutical and nutraceutical
industries. The differential behavior observed between the hybrids also suggests the need to
evaluate and select adequate strategies to process and add value to the hulls of sunflower hybrids
with differential structural characteristics.
Aknowledgments
The authors acknowledge the financial support from National Agency for Scientific and
Technological Promotion (ANPCyT), National University of the Center of the Province of Buenos
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Aires and Scientific Research Commission of the Province of Buenos Aires (CIC), Argentina. The
authors wish to thank INTA’s Agricultural Experimental Station for providing sample material.
Interest conflict
All the authors declare that they have no conflict of interest and have no competing
financial interest for the work covered in this paper.
Nomenclature
d.b.
dry base
g
relative centrifugal force
GAE
gallic acid equivalent
CE
catechin equivalent
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