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Effect of traditional sun-drying and oven-drying on carotenoids and phenolic compounds of apricot (Prunus armeniaca L.)

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Background: The indubitable role of phytochemicals such as carotenoids and phenolic compounds in human health has prompted the researchers to study the factors affecting the stability and the availability of these compounds. Aims: This study investigates the effect of two drying processes; oven-drying (OD) and traditional sun-drying (TSD) on carotenoids and phenolic compounds of apricots. Material and Methods: OD was performed at 65°C, and TSD was performed by direct exposure of apricot to sunlight at daytime temperatures around 40°C and relative humidity between 25 and 35%, following an Algerian traditional method of drying. Carotenoids and phenolic compounds were extracted, and then total carotenoids (TC), total phenolic compounds (TPC), total flavonoids (TF) and total tannins (TT) were spectrophotometrically quantified. The free radical scavenging activity (FRSA) of the phenolic extracts was measured by the DPPH method. Results: Carotenoids and phenolic compounds were significantly affected by both drying methods. OD decreased TC and TT by 44% and 12%, respectively, and increased TPC and TF by 4%. TDS affected negatively all the measured components, where TC, TPC, TF, and TT decreased by 67%, 15%, 43%, and 36%, respectively. However, the highest FRSA was reported for the TSD apricots (40%) followed by OD apricots (36%), and fresh apricots (32%). Conclusions: The effect of drying on apricot antioxidants depends on the applied drying method and the studied component. The direct sunlight exposure and the duration of drying condemned TSD to be more harmful on carotenoids and phenolic compounds compared to OD, where carotenoids where more fragile during TSD. In addition, OD improved the content of phenolic compounds by improving their extractability. However, TSD apricots seem to be a better source of free radical scavenging compounds. Keywords: Apricot, traditional sun-drying, oven-drying, carotenoids, phenolic compounds.
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Nor. Afr. J. Food Nutr. Res. I JulyDecember 2019 I Volume 3 I Issue 6
Nor. Afr. J. Food Nutr. Res. 2019; 3(6): 186-194
https://doi.org/10.51745/najfnr.3.6.186-194
https://www.najfnr.org
Effect of traditional sun-drying and oven-drying on carotenoids and
phenolic compounds of apricot (
Prunus armeniaca
L.)
Ala eddine Derardja 1 and Malika Barkat 1 *
1 Laboratoire BIOQUAL, Département de Biotechnologie, INATAA, UFMC1, Algérie.
1 Introduction
Fruits are excellent sources of macro and micronutrients,
particularly bioactive compounds such as vitamins and
antioxidants. Nowadays, it’s clear that antioxidants as
phenolic compounds, carotenoids, and vitamin C impart
numerous health benefits, where the prevention of some
socially significant diseases (like cancer and cardiovascular
diseases), has been associated with consumption of fresh
fruits and vegetables [1,2]. Plant antioxidants are
phytochemicals that can prevent the oxidation of a
biological substrate. Thus, protecting food and tissues from
damages that can be caused by free radicals [3]. Apricots
are widely distributed fruits, due to their specific sweet
flavor and color. Every year, more than 4.2 million tons are
produced [4]. Furthermore, apricot constitutes one of the
most cultivated fruits in the North African region,
particularly in Algeria, which covers more than 6 % of the
world's production [4]. Apricots provide significant health
benefits because of their high content in antioxidants,
primarily phenolic compounds and carotenoids [5,6].
Phenolics represent the predominant phytochemicals
present in apricots [5]. These compounds are a structurally
diverse class of phytochemicals and they occur as plant
secondary metabolites, they are defined by the presence of
at least one aromatic ring bonded directly to one or more
Original Article
A R T I C L E I N F O
A B S T R A C T
Article history:
- Received 29 June 2019
- Accepted 06 October 2019
- Published 10 October 2019
* Corresponding author info:
Pr. Malika BARKAT
Email: barkat.inataa@yahoo.f r
Tel. +213 31600246
Access this article online
Quick Response Code
https://doi.org/10.51745/najfnr.3.6.186-19
4
Background: The indubitable role of phytochemicals such as carotenoids and phenolic compounds in
human health has prompted the researchers to study the factors affecting the stability and the availability
of these compounds. Aims
:
This study investigates the effect of two drying processes; oven-drying (OD)
and traditional sun-drying (TSD) on carotenoids and phenolic compounds of apricots.
Material and
Methods
:
OD was performed at 65°C, and TSD was performed by direct exposure of apricot to sunlight
at daytime temperatures around 40°C and relative humidity between 25 and 35%, following an Algerian
traditional method of drying. Carotenoids and phenolic compounds were extracted, and then total
carotenoids (TC), total phenolic compounds (TPC), total flavonoids (TF) and total tannins (TT) were
spectrophotometrically quantified. The free radical scavenging activity (FRSA) of the phenolic extracts
was measured by the DPPH method.
Results
:
Carotenoids and phenolic compounds were significantly
affected by both drying methods. OD decreased TC and TT by 44% and 12%, respectively, and increased
TPC and TF by 4%. TDS affected negatively all the measured components, where TC, TPC, TF, and
TT decreased by 67%, 15%, 43%, and 36%, respectively. However, the highest FRSA was reported for
the TSD apricots (40%) followed by OD apricots (36%), and fresh apricots (32%). Conclusions
:
The
effect of drying on apricot antioxidants depends on the applied drying method and the studied
component. The direct sunlight exposure and the duration of drying condemned TSD to be more
harmful on carotenoids and phenolic compounds compared to OD, where carotenoids where more fragile
during TSD. In addition, OD improved the content of phenolic compounds by improving their
extractability. However, TSD apricots seem to be a better source of free radical scavenging compounds.
Keywords
:
Apricot, traditional sun-drying, oven-drying, carotenoids, phenolic compounds.
eISSN: 2588-1582
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Derardja & Barkat Traditional sun-drying and oven-drying effects on carotenoids and phenolic compounds of apricot
hydroxyl groups [2]. Along with their antioxidant activity,
Phenolics showed several further biological characteristics
such as antimicrobial, anti-inflammatory, and immuno-
stimulatory activities [7]. Flavonoids are water-soluble
phenolics that show strong antioxidant activities, they
constitute the largest group of polyphenols, with more than
5000 identified compounds [8]. Carotenoids are a large
family of lipophilic compounds that are responsible for the
orange color of apricots; they play a significant role in light-
harvesting and in protection against photodamage in
plants [9]. Carotenoids have been found to exhibit
important antioxidant activity and help in preventing
chronic diseases such as cardiovascular disease and skin
cancer [10]. Furthermore, they are referred to as provitamin
A since they can be transformed
in vivo
to active vitamin
A[9, 10].
Apricots are climacteric fruits that undergo fast maturation
after harvesting, which considerably limits their period of
storage. Thus, different preservation methods such as
drying and canning are habitually applied to preserve the
fruits. Drying is the most common method to preserve
apricots and extend their availability [11]. The process
reduces the moisture content of apricots to a degree that
allows safe storage for a longer period [12]. However,
several studies reported that the antioxidant content of
fresh fruits can be affected by processing techniques, which
can increase or decrease their content [8, 13, 14].
Sun-drying of fruits and vegetables is one of the oldest
forms of food preservation methods. In Algeria, traditional
sun-drying of apricot remains the most practiced method.
The reason behind this is that sun-drying is a simple
method, requiring low capital, simple equipment, and low
energy input. The traditional process of drying, applied in
Algeria, is different from that usually reported in the
literature, where apricots are neither blanched, nor treated
with sulfates to prevent browning. Instead, apricots are
treated with salt as a preservative agent and then dried.
This method provides to the dried apricots specific
organoleptic properties, where the color of the product is
brown to dark with a salty flavor. Thus, there is a lack of
knowledge on the effect of this traditional procedure on
apricot antioxidants. For this reason, the current work
investigates the effects of traditional sun-drying (TSD) on
apricot antioxidants, primarily polyphenols, flavonoids,
tannins, and carotenoids. The effect of oven drying (OD)
was also investigated for comparison.
2 Material and Methods
2.1 Plant materials
Fruits of
Prunus armeniaca
L. (cv. Louzi) were collected from
the N’gaous region of Algeria at commercial maturity.
Apricots were directly transported to the laboratory, rinsed
with tap water and stored at 4°C until utilization.
2.2 Drying process
2.2.1 Oven-drying
Fruits were dried in a ventilated laboratory oven (Memmert
ULE 600, Germany) at a drying temperature of 65°C (Figure
1). The temperature of 65°C constitutes the average
temperature used by food technologists to dry apricot [15-
18]. Samples of fresh apricots were halved, pitted, and then
placed in the oven, on the steel sieved trays, which were
designed to increase air passage from both surfaces.
Before starting the drying process, the oven was run for 30
min to obtain steady-state conditions. The suitable dryness
level (moisture around 25 %, according to
CODEX STAN
130-1981
) was reached in 14 to 15 hours. Dried apricots were
placed into polyethylene bags and stored at 4°C until
subsequent analysis.
Figure 1: Simple schematiza tion of the drying processes
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Derardja & Barkat Traditional sun-drying and oven-drying effects on carotenoids and phenolic compounds of apricot
2.2.2 Traditional sun-drying
Fresh apricots were halved, pitted, divided on a metal
plate (covered with a cloth) and then dried by direct
exposure to sunlight, with an overall maximum daytime air
temperature of around 40°C for nine days (starting from
mid-June). After that, dried apricots were washed, treated
with salt by pulverization, and then, dried for three other
days in the shadow to evaporate the residual water from
the washing step (Figure 1). Dried apricots were placed
into polyethylene bags and stored at 4 °C until
subsequent analysis. During the drying process, the
relative humidity of the air was between 25 and 35%, the
days were sunny with no precipitation. This traditional
sun-drying method is a common process applied by the
farmers and the families in several regions in Algeria,
aiming to preserve the excess of production and make
apricots available for longer periods.
2.3 Chemical properties
Aiming to facilitate the extractability of apricot antioxidants
and to standardize the analysis conditions for all samples,
dried apricots were rehydrated for 24 h at room
temperature. The exact and identical amount of water lost
during the drying process was added during the
rehydration (to reach the same water content as the fresh
fruit), while the fresh samples were directly analyzed [19].
Before analysis samples were homogenized for two
minutes using a Hand Blender Beaker. The following
analyses were performed on the obtained purees: moisture
content (MC) and dry-matter content (DM). They were
measured (%) in a vacuum oven for 3 h at 105 °C (NF V 05-
108, 1970) (for fresh, dried and rehydrated fruit), pH,
measured using a digital pH meter (NF V 05-108, 1970).
Acidity was determined as gram of citric acid per 100 g of
samples by titration with 0.1 N sodium hydroxide to
endpoint (pH 8.3) (NF V 05-101,1974). Ash content (%) was
obtained using a muffle furnace at 550 °C for 5 hours (NF
V 05-113,1972).
2.4 Measurement of total carotenoids
Total carotenoids were extracted according to the method
of Rodriguez-Amaya [20] with optimization. Five grams of
sample were extracted with 100 mL of methanol/petroleum
ether (1:9, v/v) by using a high-speed homogenizer, and the
mixture was transferred to a separating funnel. The
petroleum ether layer was filtrated through sodium sulfate,
transferred to a volumetric flask, and then the volume was
completed to 100 mL with petroleum ether. Finally, the total
carotenoid content was measured at 450 nm using a
Shimadzu 1600- UV spectrophotometer. The results were
expressed in mg β-carotene equivalent (β-CE/100 g DM).
2.5 Phenolic compounds analysis
2.5.1 Phenolic extract preparation
Phenolic compounds were extracted using the method
described by Ali
et al.
[21]
.
Five grams of fruit puree was
taken from the homogenate and diluted to 30 mL with 80%
methanol and clarified by centrifugation (SEGMA 3-30K) at
10,000 × g for 15 min. The extract was filtered through a
Whatman no. 1 filter paper.
2.5.2 Total phenolic compounds measurement
Total phenolic compounds (TPC) were measured by using
the FolinCiocalteu assay as described by Singleton
et al
.
[22] with minor modification. The crude phenolic extract,
0.5 mL was first diluted to 5 mL with 80% methanol, then
0.5 mL of 2 N FolinCiocalteu reagent and 0.5 mL of 20%
sodium carbonate solution were added. The mixture was
then allowed to stand for 60 min at room temperature and
the absorbance was measured at 765 nm using a
Spectrophotometer. Total phenolics were estimated by
calibration curve prepared with concentrations of 0.01-0.25
mg/mL of gallic acid. The results were expressed in mg
gallic acid equivalent (GAE) / 100 g DM.
2.5.3 Total flavonoids measurement
Total flavonoids (TF) were determined using the
colorimetric method described by Bahorun
et al.
[23]. From
the crude phenolic extract, 1 mL was mixed with 1 mL of a
2% AlCl3-6H2O solution. After 10 min, the absorbance was
measured immediately at 430 nm using a
Spectrophotometer. The results were expressed as mg
quercetin equivalent (QE) /100 g DM, according to a
calibration curve prepared with concentrations of 1-40
μg/mL of quercetin.
2.5.4 Total t annins measurement
The estimation of the total tannins (TT) content was carried
out by the method described by Hagerman & Butler [24]. 1
mL of the phenolic extract was mixed with 2 mL of bovine
serum albumin solution (1 mg/mL) prepared in 200 mM
acetate buffer, pH 4.9. After immediate stirring and
incubation for 24 hours at 4 °C, the mixture was centrifuged
for 15 min at 4000 rpm. The supernatant was discarded and
the pellet was recovered and washed with 200 mM acetate
buffer, pH 4.9. The resulting precipitate was dissolved in 4
mL of sodium-dodecyl-sulfate/
Tri-ethanol-amine
(1:5, w/v)
solution, pH 9.5, and then 1 ml of the ferric chloride solution
(100 mM HCl, 10 mM FeCl3) was added. After incubation for
15 min, the absorbance was read at 510 nm on a
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Derardja & Barkat Traditional sun-drying and oven-drying effects on carotenoids and phenolic compounds of apricot
Spectrophotometer. The amount of tannins was calculated
by a calibration curve prepared with tannic acid (0.1-1.25
mg/ml). The results are expressed in mg tannic acid
equivalent (TAE)/100 g DM.
2.5.5 Free radical scavenging activity measurement
Free radical scavenging activity (FRSA) was measured using
DPPH (2,2-diphenyl-l-picrylhydrazyl) free radical according
to the protocol described by Kuskoski
et al.
[25]. 0.1 ml of
crude phenolic extract was taken in the test tube and 3.9
mL of 100 μM DPPH (2,2-diphenyl-l-picrylhydrazyl) solution
was added, then the mixture was shaken vigorously and
incubated for 30 minutes at room temperature.
Absorbance was measured at 517 nm using a
Spectrophotometer. The DPPH solution, freshly prepared
with 80% methanol, gives an absorbance of 1.1 at 517 nm.
Radical scavenging activity was calculated as % inhibition
of DPPH radical using formula (01):
%Inhibition =Acontrol Asample
Acontrol
×100… … (01)
Acontrol : Absorbance of the control reaction (blank with
methanol and DPPH solution).
Asample : Absorbance of the sample reaction (phenolic
extract with methanol and DPPH solution).
2.6 Statistical analysis
All analyses were carried out in triplicate and the
experimental data were reported as means ± standard
deviation (SD). The data were subjected to an analysis of
variance (one-way ANOVA). The significant difference was
determined by Tukey's multiple range test (
p
≤ 0.05) using
XL-STAT software Version 2009.
3 Results
The aim of the current study is to investigate the effect of
traditional sun-drying (TSD) and oven drying (OD) on
apricot antioxidants (carotenoids and phenolic
compounds). Prior to the measurements on antioxidants,
fresh and dried apricot were first assayed for humidity, ash
content, pH and acidity. The results are shown in table 1.
Table 1: Chemical properties of fresh and dried apricots
Drying
process
MC (%)
DM (%)
Ash (%)
pH
TA (%)
FA
85.24 ±
0.23
14.76 ±
0.23
0.734 ±
0.08
3.94 ±
0.07
0.59 ±
0.06
TSD
21.05 ±
0.56
79.95 ±
0.56
4.26 ±
0.18
4.03 ±
0.17
3,62 ±
0,13
OD
26.06 ±
0.74
73.94 ±
0.74
2.82 ±
0.08
4.16 ±
0.05
2.87 ±
0.08
FA, fresh apricot; TSD, traditional sun drying; OD, oven drying; MC, moisture
content; DM, dry matter content; TA, titratable acidity. All the values are means
of three replications +SD.
Moisture content decreased from 85.24% for fresh apricot
to 21.05% and 26.06% for TSD and OD dried apricots,
respectively. As a result, dry matter and ash content
decreased after the drying processes, as well as TA.
However, a slight increase in pH was observed for the dried
apricots (Table 1).
Total Carotenoids (TC) were assessed before and after the
drying processes. Data are reported on a DM basis in figure
2. Significant differences between the TC of fresh and dried
apricots (p<0.0001) were reported. OD had remarkably
affected TC content of apricots; the drying process
decreased TC from 46.4 ± 6.2 mg β-CE/100 g DM to 25.8
± 2.4 mg β-CE/100 g DM, which represents a loss of 44%.
Furthermore, compared to OD, TSD was much harmful to
TC, where the traditional process provoked a more
significant decrease of 67%.
Figure 2: Effects of oven-drying (OD) and traditional sun-
drying (TSD) on apricot total carotenoids (TC)
FA, fresh apricot; β-CE, β-carotene equivalent; DM, dry matter content. All the
values are means of three replicatio ns +SD. The same letters i ndicate the absence
of significant differences (p<0.05).
The effects of TSD and OD on total phenolic compounds
(TPC), total flavonoids (TF), total tannins (TT), and Free
radical scavenging activity (FRSA) of apricots are reported
on a DM basis on figure 3. All measured parameters were
significantly affected (p<0.05) by both drying methods
(TSD and OD). TSD decreased remarkably the amount of
TPC (Figure 3.a), TF (Figure 3.b), and TT (Figure 3.c) of
apricots. The drying process caused significant losses of
15%, 43%, and 36%, respectively. However, for the OD, a
decrease of 12% in TT after the drying process was
recorded, while a slight increase of 4% was observed in TPC
and TF.
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Derardja & Barkat Traditional sun-drying and oven-drying effects on carotenoids and phenolic compounds of apricot
FRSA (%) results are presented on figure 3.d. In contrast to
our previous results (TPC, TF, and TT), FRSA increased
significantly in dried apricot, and the heist FRSA was
reported for the TSD. The methanolic extract of the dried
apricot showed a radical scavenging activity of 40.1 ± 0.8%,
followed by OD (35.9±1.7%), and fresh apricot (31.7 ± 1.2%).
Figure 3: Effects of oven-drying (OD) and traditional sun-drying (TSD) on apricot total phenolic compounds (TPC), total flavonoids (TF),
total tannins (TT), and Free radical scavenging activity (FRSA)
a: TPC, b: TF, c: TT, d: FRSA. FA, fresh apricot, DM, dry matter content, β-CE: β-carotene equivalents, GAE: gallic acid equivalent, QE: quercetin equivalent, TAE: tannic acid
equivalent. All the values are means of three replications +SD. The same letters indicate the ab sence of significant differences (p<0.05).
4 Discussion
The comparison between our findings and the different
works on apricots showed that our values are included in
the ranges reported by Akin
et al.
[26] for the humidity
(74.19 - 88.17%) and ash content (0.50% - 0.89%), and the
intervals indicated by Leccese
et al.
[6] for pH (3.35 - 4.41)
and acidity (0.48 - 2.28%). The important loss of water
during the drying process resulted in a concentration of the
different components of apricot, which explains the
increase in ash content and acidity (Table 1). The titratable
acidity of apricot after the TSD (3.62%) was higher than the
titratable acidity of apricot after the OD (2.87%). This can
be due to the difference in drying conditions (mainly time
and temperature) between the two processes, where
apricot (climacteric fruit) can carry on the post-harvest
maturation during TDS [11]. The drying temperatures (40°C)
during TDS promote the physiological and biochemical
reactions, including organic acids synthesis. However, the
drying temperatures (65°C) during OD are relatively high,
thus the physiological and the biochemical reactions are
restrained. High acidity for sun-dried apricots was also
reported by Madrau
et al.
[15] (4.67 - 7.33%) and Bolin [27]
(3.8%). The ash content of the traditional sun-dried apricots
was superior then the ash content of the oven-dried
apricots too. This difference is mostly caused by the salt
added during the process. Contamination by dust during
the TSD may have also contributed to the ash content
increase. Both drying methods have significantly decreased
the carotenoids content of apricots (Figure 2). OD
decreased apricot carotenoids by 44% of the initial content.
These results are comparable to those of Fratianni
et al.
[16],
where they reported significant losses of 50 % in total
carotenoids for apricots dried at temperatures between 60
and 70 °C. In the same context, Karabulut
et al.
[17]
recorded a decrease of 40% in β-carotene content after
drying at 70 °C, and surprisingly they reported more losses
(60%) by decreasing the drying temperature to 60 °C. The
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thermal damages caused by drying were directly
proportional to the temperature used and the time
operated in the process. It was mentioned that the heat
applied during drying softens the cell walls, making them
fragile and easily separated [16,17]. Therefore, the
carotenoids, usually stable within the original structure,
become highly sensitive to external agents such as heat,
oxygen, and light [16]. However, carotenoids were more
sensitive to TSD. The traditional process caused the most
significant losses, where the measurement of total
carotenoid has highlighted a more significant decrease of
67% compared to OD. It has been reported that oven
drying and additional conventional drying methods have
several advantages over sun-drying. García-Martínez
et al.
[19] related these advantages to the fact that conventional
drying methods are more rapid and the fruits are not in
contact with the open environment during the process. Our
results are consistent with those of Korekar
et al.
[28], where
the authors reported a loss of 65% of β-carotene content
for the sun-dried apricots. Furthermore, in a recent study,
performed by Vega-Gálvez
et al.
[18] on the effect of hot-
air drying temperatures (40-80°C) on apricot bioactive
compounds, the results showed that the increase of drying
time led to more damage than the increase of temperature.
Moreover, the same authors reported the more significant
carotenoids content decrease (53% loss) at the lowest
temperature (40°C). The principal cause of carotenoids
degradation, during the TSD, was the direct exposure of
apricot to oxygen and sunlight. The destructive effect of
oxygen and sunlight on carotenoids was confirmed by
several authors [16-19, 29]. The exposure to oxygen during
drying causes the generation of peroxides and oxidizing
free radicals, which can cause a serious carotenoids loss
[29]. Yang
et al.
[30] reported that carotenoids are sensitive
to oxidation and can decompose, even if the samples were
kept in the presence of traces of oxygen. The degradation
of carotenoids can also result from photo-oxidation in the
presence of light [31].
The investigated apricots in the current study were found
to be a suitable source of phenolic compounds (451.6 ± 11.3
mg GAE / 100 g DM). The comparison with other studies
shows that our results are higher than the ranges (319 and
413 mg GAE / 100 g DM) as reported by Milošević
et al.
[32].
As shown on figure 3.a, drying methods affected
significantly apricots’ phenolic compounds. In the last
decades, numerous works investigated the effect of
different treatments on phenolic compounds. Yet, data are
not to seem correlated and even contradictory [33]. Most
researchers reported a negative effect (decrease in
phenolic compounds concentration) of heat treatments on
phenolic compounds [13, 34,35]. On the other hand, several
authors stated an increase in phenolic compounds after
heat treatments. In our study, we witnessed both effects,
where OD caused a slight increase in TP and TF, while TSD
led to a significant decrease in TP, TF, and TT.
The increase, detected in TPC and TF after OD, was also
reported in a previous study on apricot by Hussain
et
al.
[36], where the authors detected an increase of 11.6-
16.4% in the phenolic compounds concentration after
drying. In the same angle, Santos
et
al.
[37] studied the
effect of drying at 60 °C on the phenolic compounds of
pears, and reported an increase of 2.4-15% in TPC.
However, Madrau
et
al.
[15] reported a decrease in TPC of
apricots dried at a lower temperature (55°C). In addition,
Vega-Gálvez
et al.
[18] reported a significant decrease of
TPC (>73%), and TF (>61%) for dried apricots at
temperatures between 60 and 70 °C. The increase of TPC
and TF can be explained by the improvement of phenolic
compounds extractability, due to the relatively high
temperature (70 °C) during the drying process, where it has
been reported that high temperature facilitates the
extraction of phenolic compounds [38-40]. Phenolic
cosmpounds occur more often conjugated in soluble and
insoluble forms, covalently bound to structural
components of the cell wall (cellulose, hemicelluloses, and
lignin). Bound phenolic compounds constitute an average
of 24% of the fruits TPC, and heat treatments are likely to
release those bound phenolic compounds [41]. Brunton
[42] reported that, in addition to the better extractability of
phenolic compounds during drying, the increase of TPC
and TF can be due to the depolymerization of phenolic
compounds with high molecular weights such as tannins.
This statement agrees with our findings, where the increase
of TPC and TF after OD was accompanied by a decreased
in TT.
Unlike OD, TSD has caused significant losses of apricots
phenolic compounds, where TPC, TF, and TT decreased by
15%, 43%, and 36%, respectively. This decrease can be
explained by the enzymatic oxidation of phenolic
compounds. Madrau
et al.
[15] reported that drying
apricots for a long period in the presence of oxygen
promotes the degradation of phenolic compounds by
polyphenol oxidase (PPO). This enzyme is responsible for
the oxidation of phenolic compounds to quinines. The
enzymatic oxidation is followed by non-enzymatic
polymerization of the resulted quinones into dark/brown
polymers called melanins [43]. Apricot PPO remains active
at drying temperature below 55 °C [44], and since TSD was
performed at temperatures ~ 40 ° C, enzymatic browning
is mostly the main cause of phenolic compounds decrease
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Derardja & Barkat Traditional sun-drying and oven-drying effects on carotenoids and phenolic compounds of apricot
in TSD apricots. This was also visually confirmed, where the
dried apricots had dark colors. Our results are in agreement
with the results obtained by Vega-Gálvez
et al.
[18], where
the authors attributed the decrease in TPC and TF observed
during drying at 40 °C to the PPO activity.
The antioxidant activity increased significantly after the OD,
this can be explained by the increase reported previously
in TPC and TF, where phenolic compounds are known for
their FRSA. However, while the expectations shifted toward
a decrease in FRSA after TSD, surprisingly, the results
showed a significant increase in FRSA (Figure 3.d). These
results are similar to those of Madrau
et al.
[15] and Hussain
et al.
[36], the authors reported a significant increase in
FRSA for dried apricots, despite the reduction in TPC.
However, Vega-Gálvez
et al.
[18] reported a decrease in
FRSA for dried apricots at temperatures between 40 and
80°C. According to Pokorny & Schmidt [45], FRSA of
processed fruits may be enhanced by the development of
new antioxidants, such as the products of browning
reactions. Furthermore, Gan
et al.
[46] reported an increase
in the antioxidant activity for the dried mung bean, which
was also accompanied by an increase in browning. The
same findings were reported by Lee
et al.
[47] for dried
onions, the authors indicated that the antioxidant activity
depends more on browning during drying than on
phenolic content.
5 Conclusion
The main obtained results showed that TSD conditions,
such as direct sunlight exposure and the longtime of the
drying process, are parameters that affect negatively
carotenoids and phenolic compounds of apricots. These
conditions promoted the carotenoids photo-oxidation and
the enzymatic oxidation of phenolic compounds (by PPO).
Thus, OD caused less damage to carotenoids and phenolic
compounds compared to TSD. The advantages of OD are
the short period of drying, and the fruits are not exposed
to open air, which has resulted in better preservation of
carotenoids and phenolic compounds. However, despite
the destructive effect of TSD on carotenoids and phenolic
compounds, the process increased the FRSA of the
phenolic extract. The enzymatic oxidation of the phenolic
compounds during TSD promoted the generation of new
compounds with high antioxidant properties. Thereby, the
traditionally sun-dried apricots are a better source of
antioxidants.
Acknowledgment
The authors wish to thank the Algerian Ministry of Higher
Education and Scientific Research (MESRS) for the financial
support of this work.
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Cite this article as: Derardja, A., & Barkat M. (2019). Effect of traditional sun-drying and oven-dryi ng on carotenoids and phenolic compounds of apricot (
Prunus armeniaca
L.).
The North African Journal of Food and Nutrition Research,
3(6):186-194. https://doi.org/10.51745/najfnr.3.6.186-194
© 2019 The Author(s). Thi s is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, dis tribution, and
reproduction in any medium, provided the original work is properly cited.
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