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Citation: Rodríguez-Blázquez, S.;
Gómez-Mejía, E.; Rosales-Conrado,
N.; León-González, M.E.;
García-Sánchez, B.; Miranda, R.
Valorization of Prunus Seed Oils:
Fatty Acids Composition and
Oxidative Stability. Molecules 2023,28,
7045. https://doi.org/10.3390/
molecules28207045
Academic Editors: Petko Denev,
Stela Dimitrova and Ana M. Dobreva
Received: 14 September 2023
Revised: 9 October 2023
Accepted: 10 October 2023
Published: 12 October 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
molecules
Article
Valorization of Prunus Seed Oils: Fatty Acids Composition and
Oxidative Stability
Sandra Rodríguez-Blázquez 1,2 , Esther Gómez-Mejía1, Noelia Rosales-Conrado 1,
María Eugenia León-González 1, * , Beatriz García-Sánchez 2and Ruben Miranda 2
1Department of Analytical Chemistry, Faculty of Chemistry, Complutense University of Madrid,
Complutense Avenue, 28040 Madrid, Spain; sandro08@ucm.es (S.R.-B.); egomez03@ucm.es (E.G.-M.);
nrosales@ucm.es (N.R.-C.)
2Department of Chemical Engineering and Materials, Faculty of Chemistry, Complutense University of
Madrid, Complutense Avenue, 28040 Madrid, Spain; beatriga@ucm.es (B.G.-S.); rmiranda@ucm.es (R.M.)
*Correspondence: leongon@ucm.es
Abstract:
Prunus fruit seeds are one of the main types of agri-food waste generated worldwide
during the processing of fruits to produce jams, juices and preserves. To valorize this by-product,
the aim of this work was the nutritional analysis of peach, apricot, plum and cherry seeds using the
official AOAC methods, together with the extraction and characterization of the lipid profile of seed
oils using GC-FID, as well as the measurement of the antioxidant activity and oxidative stability
using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging method. Chemometric
tools were required for data evaluation and the obtained results indicated that the main component
of seeds were oils (30–38%, w). All seed oils were rich in oleic (C18:1n9c) and linoleic (C18:2n6c)
acids and presented heart-healthy lipid indexes. Oil antioxidant activity was estimated in the
range
IC50 = 20–35 mg·mL−1
, and high oxidative stability was observed for all evaluated oils during
1–22 storage
days, with the plum seed oil being the most antioxidant and stable over time. Oxidative
stability was also positively correlated with oleic acid content and negatively correlated with linoleic
acid content. Therefore, this research showed that the four Prunus seed oils present interesting healthy
characteristics for their use and potential application in the cosmetic and nutraceutical industries.
Keywords:
Prunus seed oils; peach seeds; apricot seeds; plum seeds; cherry seeds; fatty acids;
antioxidant activity; oxidative stability; by-product valorization
1. Introduction
Currently, there is a high level of interest in the search for new alternatives for the
recovery of waste from the agri-food industry [
1
,
2
]. During the industrial processing
of fruits, a large amount of waste and by-products such as peels, stones and seeds are
generated [
1
,
3
,
4
]. The deposition of these materials in landfill sites has significant negative
food-security, economic and environmental impacts [
5
]. Therefore, to reduce environmental
pollution along with economic losses, different research studies have reported that agri-
food waste material could be exploited as a source of high-value-added compounds that
could be applied in the cosmetic, pharmaceutical and nutraceutical sectors [2,3,6].
The processing of some members of the Rosaceae family in the genus Prunus, including
peach (Prunus persica), apricot (Prunus armeniaca), plum (Prunus domestica) and sweet cherry
(Prunus avium), is of great importance worldwide [
7
]. According to the 2023 campaign for
stone fruits [
8
], 110,692 tons of apricot, 805,368 tons of peach, 164,685 tons of plum and
140,166 tons of cherry were produced in Spain.
All Prunus species are highly appreciated by consumers and, thus, they are being
studied not only because of their taste, color and sweetness, but also for their nutritional
composition and bioactive properties [
9
,
10
]. Their entire stone is divided into a central
softer part known as the kernel or seed, and an outer hard part named the shell. Depending
Molecules 2023,28, 7045. https://doi.org/10.3390/molecules28207045 https://www.mdpi.com/journal/molecules
Molecules 2023,28, 7045 2 of 18
on the fruit, the seed of the stone accounts for approximately 15–30 wt.% of the entire stone,
while the remaining 70–85 wt.% corresponds to the stone’s shell [
11
]. Prunus seeds are
one of the main components discarded during the production of juices and jams, and in
other processing industries. This waste constitutes a huge nutritional loss, since seeds are a
good source of unsaturated fatty acids, proteins, dietary fibers, carbohydrates, polyphenols,
vitamins and other bioactive compounds [12,13]. The presence of proteins, carbohydrates
and dietary fibers is essential for the maintenance of human tissues, the production of
neurotransmitters, the generation of energy reserves and the proper functioning of the
human intestine, among others [14].
Among the main components of seeds, due to their multiple bioactivities, are the
oils [
12
]. The levels of bioactive compounds in seed oil depends on the extraction method
used. Although non-traditional techniques are currently used that reduce the use of sol-
vents, such as cold pressing, supercritical methods, ultrasonic-assisted extraction and
microwave-assisted extraction [
15
], the reference method par excellence is Soxhlet extrac-
tion. Due to its simplicity and high extraction yield, it is one of the most widely used
techniques for the recovery of fatty acids from oils [
16
]. The most common solvent used
in this extraction technique is n-hexane due to its high solubility with oils, low cost, high
volatility, low boiling point and easy removal from solids [17].
Prunus seed oils are mainly characterized by triacylglycerides of different chemical
natures. The main fatty acids found in Prunus seed oils are oleic (52–66%), linoleic (25–35%)
and palmitic acids (3–10%) [
9
,
18
]. The high content of unsaturated fatty acids (UFA) in the
oils reduces the concentration of low-density lipoproteins (LDL) which, when circulating
in the body, are deposited in the blood vessels, reducing dysrhythmias, mortality caused
by coronary disease and the rate of atherosclerosis, as well as blood pressure [
19
,
20
]. In
addition, the high content of polyunsaturated fatty acids (PUFA) in seed oils has been
related to the development and/or regeneration of cell membranes and a protective effect
against dementia and Alzheimer’s disease [
19
,
21
]. Furthermore, oils are characterized by a
low content of saturated fatty acids (SFA), which increase LDL protein levels and the risk
of coronary heart disease [
22
]. A PUFA/SFA ratio below 0.45 in the diet is a risk factor for
increased blood cholesterol levels [23].
The health quality of lipids, based on fatty acid composition, is determined using
indexes. The desirable fatty acid (DFA) index provides information on the hypocholes-
terolemic properties (reduction of total cholesterol) of the lipids analyzed [
24
]. The hypoc-
holesterolemic/hypercholesterolemic (HH) ratio can become an indicator of the cholesterol
effect of a fat source. Atherogenicity (AI) and thrombogenicity (TI) indexes are also used to
indicate the risk of developing cardiovascular irregularities [
25
]. The n-6/n-3 PUFA ratio is
another important parameter to consider when establishing the nutritional value of oils as
it is related to lipid metabolism, neurogenesis and cell apoptosis [12,26,27].
In addition to the importance of knowing the content of fatty acids present in the
oils, it is also important to know their antioxidant activity and their stability against lipid
oxidation [
18
]. Oil lipid oxidation is one of the main causes of the loss of quality in
color, taste, aroma and nutritional value due to the degradation of essential fatty acids
and the production of toxic compounds that can contribute to the development of cancer,
atherosclerosis, heart disease and allergic responses [
28
]. The oxidation process depends
mainly on exposure to light, the temperature, the presence of oxygen, the composition
of fatty acids and the composition of antioxidant compounds such as polyphenols and
tocopherols [
29
,
30
]. Bozan et al. [
31
] found that a high polyunsaturated content of linolenic
acid and long-chain fatty acids reduces the oxidative stability of the oils. In addition,
Redondo et al. [
32
] studied the relationship between the lipid composition and oxidative
stability of 22 different types of fats and observed that a higher oxidative stability correlates
with a lower SFA content.
Commonly used methods to determine the oxidative stability of lipids include the
determination of the peroxide value; the oxidative stability index; the determination of the
induction time in the Rancimat test; the determination of the amount of aldehydes formed
Molecules 2023,28, 7045 3 of 18
(TBA method) such as lipid oxidation by-products; and the 2,2-diphenyl-1-picrylhydrazyl
(DPPH) free-radical scavenging method [
33
,
34
]. In addition, kinetic methods are used
in conjunction with these methods to evaluate the degradation process that lipids un-
dergo [35].
Therefore, to study the possible valorization of Prunus seeds as functional ingredients,
the present work aims to perform a nutritional analysis of the seeds of P. armeniaca,P. persica,
P. avium and P. domestica, together with the extraction and characterization of the oils
obtained from the mentioned seeds in terms of the fatty acid profile, lipid quality indexes
and antioxidant activity.
2. Results and Discussion
2.1. Evaluation of the Nutritional Analysis of Prunus Seeds
The characterization of the approximate composition of peach, apricot, plum and
cherry seeds is presented in Table 1. It was performed in terms of the moisture, ash,
fat, crude fiber, protein and carbohydrates content, which allowed us to estimate the
nutritional value and quality of seed by-products and, thus, their potential applicability as
functional ingredients.
Table 1. Nutritional analysis of peach, apricot, plum and cherry seeds.
Sample Seed
(%, w)
Moisture
(%, w)
Ash
(%, w)
Fat
(%, w)
Crude
Fiber
(%, w)
Protein
Nitrogen (%, w)
Carbohydrates
(%, w)
Peach 2.4 ±0.3 a7.6 ±0.4 a6.1 ±0.1 a30 ±3a8.63 ±0.02 a35 ±2a13 ±3a
Apricot 12.4 ±0.6 b5.8 ±0.3 b4.8 ±0.4 b38 ±2b
7.49
±
0.02
b28.7 ±0.8 b15 ±3b
Plum 9.5 ±0.3 c4.7 ±0.4 c2.16 ±0.02 c37.4 ±0.4 b21.4 ±0.2 c16 ±2c18 ±2c
Cherry 10.3 ±0.5 d3.6 ±0.1 d
1.43
±
0.02
d36.0 ±0.2 b23.9 ±0.6 d10.3 ±0.7 d25 ±1d
Values are expressed as mean
±
standard deviation (n = 3), in dry weight. Values followed by a different
superscript in a column differ significantly (p-value < 0.05) according to ANOVA and Fisher’s LSD test.
As it is presented in Table 1, significant variations (p-value < 0.05) among the samples
studied were observed in the seed-to-whole stone ratio, moisture, ash, crude fiber, protein
nitrogen and carbohydrates contents. These differences were highly likely due to the plants’
genotype, but also to their geographical origin and fruit maturity stages. However, two
statistically different groups were observed in the fat content of the seeds: the first group
contained peach seeds and the other group contained apricot, plum and cherry seeds.
As can be seen in Table 1, all Prunus seeds showed low moisture content, between
3.6 and 7.6% (w), which is beneficial for storage over long periods of time, as they are not
susceptible to microorganism attack [
36
]. In addition, it is noteworthy that every single
seed studied was characterized as a suitable source of fat, with percentages between 30
and 38% (w) over the whole seed, followed by protein (10–35%, w), crude fiber (7–24%,
w) and carbohydrates (13–25%, w). In line with the results shown in Table 1, kernels are
known to be particularly rich in oil [
37
]. In fact, the seeds with the highest lipid content
were apricot (38
±
2%, w), plum (37.4
±
0.4%, w) and cherry (36.0
±
0.2%, w), forming a
homogeneous group statistically richer in fat content (p-value < 0.05) compared to peach
seeds (
30 ±3%
, w). The fact that seeds are rich in oils is highly relevant in the food and
cosmetic industries, making it possible to recover this waste [
38
,
39
]. On the other hand,
the presence of a high protein content is of vital importance for the strengthening and
maintenance of the muscles and bones that make up the human body, thus providing a
high energy intake [
40
]. In addition, the high content of crude fiber and carbohydrates
in seeds display several benefits, such as the reduction of cholesterol, diabetes, coronary
heart disease and even the prevention and/or treatment of obesity [
41
–
43
], showing the
high quality and the potential of these bio-residues as functional ingredients [
37
]. The
obtained results from the approximate analysis are comparable with the results of other
researchers [
37
,
44
–
48
], which found that Prunus seeds were characterized by a protein
Molecules 2023,28, 7045 4 of 18
content of 6–20% (w), a crude fiber content of 15–20% (w), an oil content of 11–57% (w), a
moisture content of 5–7% (w), an ash content of 1–3% (w) and a carbohydrate content of
18–27% (w).
2.2. Evaluation of the Physico-Chemical Quality Characteristics of Prunus Seed Oils
2.2.1. Density Determination
The oil density is an identifying quality that allows the quality and purity of the oil to
be determined [
7
]. Table 2shows the density values obtained for peach, apricot, plum and
cherry seed oils, which ranged from 0.896 to 0.917 g
·
mL
−1
, and were in agreement with
those reported by other authors [
7
,
49
]. The highest density was exhibited by the cherry
seed oil (0.917
±
0.005 g
·
mL
−1
), followed by plum seed oil (0.903
±
0.002 g
·
mL
−1
), apricot
seed oil (0.897
±
0.003 g
·
mL
−1
) and peach seed oil (0.896
±
0.001 g
·
mL
−1
). According to the
Fisher’s LSD test, three homogeneous groups (p-value < 0.05) were observed, determining
that peach and apricot oils did not differ significantly from each other at the 95% confidence
level, although they diverged significantly from plum and cherry oils. Neagu et al. [
50
]
reported that the density of vegetable oils is conditioned by their fatty acid composition,
minor constituents and temperature. Accordingly, the similarity between peach and apricot
seed oils can be likely attributed to a similar fatty acid content. Therefore, determining the
lipid composition of the oils is necessary.
Table 2. Density values of peach, apricot, plum and cherry seed oils.
Sample Density (g·mL−1)
Peach oil 0.896 ±0.001 a
Apricot oil 0.897 ±0.003 a
Plum oil 0.903 ±0.002 b
Cherry oil 0.917 ±0.005 c
Data obtained are expressed as mean
±
standard deviation (n = 3). Values with different letters in the same
column denote significant differences (p-value < 0.05) among samples according to ANOVA and Fisher ’s LSD test.
2.2.2. Fatty Acid Composition
The fatty acid profile of Prunus seed oils was determined using gas chromatogra-
phy coupled to a flame ionization detector (GC-FID) with previous derivatization to their
corresponding methyl esters following the method proposed by Lee et al. [
51
]. For the
identification of the fatty acids present in peach, apricot, cherry and plum seed oils, the
chromatogram of FAME 37 component SUPELCO standard mixture (Figure S1, Supple-
mentary Materials) and PUFA No. 3 Menhaden oil Ref 47085—standard mix (Figure S2,
Supplementary Materials) were registered. For quantification purposes, an internal stan-
dard calibration was carried out with the response factor (RF) using tridecanoic acid (C13:0)
as an internal standard. The internal standard was added directly (1 mg) before methy-
lation to correct the losses that could occur in the process of fatty acid derivatization to
methyl esters. According to data from the literature [
52
], the recovery of fatty acids after
derivatization processes ranges from 85.6 to 114.1%. The response factors (RF) for each
fatty acid in the internal standard calibration ranged from 1.069 to 1.132. The limit of
quantification (LOQ) was established as 0.33 mg
·
g
−1
and the limit of detection (LOD) was
0.1089 mg
·
g
−1
. As an example, the chromatograms of plum and cherry seed oils can be
observed in Figures S3 and S4 (Supplementary Materials), respectively. A total of 10 fatty
acids was identified in peach, apricot and plum seed oils: palmitic acid (C16:0), palmitoleic
acid (C16:1n7), margaric acid (C17:0), stearic acid (C18:0), cis-vaccenic acid (C18:1n7c), oleic
acid (C18:1n9c), linoleic acid (C18:2n6c),
α
-linolenic acid (C18:3n3), arachidic acid (C20:0)
and gondoic acid (C20:1n9). Moreover, two additional saturated fatty acids were identified
in the cherry seed oil: behenic acid (C22:0) and lignoceric acid (C24:0). The lipid content
was expressed as a percentage (%) considering a response factor (RF) of 1 and the results
are indicated in Table 3. As previously reported by Lazos et al. [
7
], Atik et al. [
53
] and
Perifanova et al. [
54
], the oils exhibited a high percentage of unsaturated fatty acids (UFA),
Molecules 2023,28, 7045 5 of 18
ranging from 86% (cherry oil) to 92.2% (apricot oil), with oleic (48.6–72.7%) and linoleic acid
(16.4–39.3%) being the dominant ones. The content of saturated fatty acids (SFA) present in
the oils varied in the range of 7.8% to 14%, with palmitic acid as the main one (5.71–8.1%).
Meanwhile, the levels of other fatty acids present in the oils were below 1% (Table 3).
Table 3. Fatty acid composition of peach, apricot, plum and cherry seed oils.
Fatty Acids Peach Oil (%) Apricot Oil (%) Plum Oil (%) Cherry Oil (%)
Palmitic acid (C16:0) (7.95 ±0.08) a(6.36 ±0.03) b(5.71 ±0.03) b(8.1 ±0.8) a
Palmitoleic acid (C16:1n7) (0.579 ±0.002) a(1.10 ±0.03) b(0.81 ±0.01) c(0.39 ±0.01) d
Margaric acid (C17:0) (0.0612 ±0.0008) a(0.051 ±0.002) b(0.0529 ±0.0001) a,b (0.092 ±0.007) c
Stearic acid (C18:0) (1.401 ±0.004) a(1.27 ±0.05) a(2.86 ±0.05) b(3.8 ±0.6) c
Cis-Vaccenic acid (C18:1n7c) (1.302 ±0.007) a(1.863 ±0.024) b(1.185 ±0.005) c(0.71 ±0.02) d
Oleic acid (C18:1n9c) (52.9 ±0.4) a(49.6 ±0.5) b(72.7 ±0.2) c(48.6 ±0.9) b
Linoleic acid (C18:2n6c) (35.4 ±0.3) a(39.3 ±0.5) b(16.4 ±0.2) c(36.1 ±0.9) a
α-Linolenic acid (C18:3n3) (0.129 ±0.006) a(0.172 ±0.008) b(0.081 ±0.001) c(0.1063 ±0.0003) d
Arachidic acid (C20:0) (0.143 ±0.006) a(0.14 ±0.01) a(0.1952 ±0.0004) a(1.3 ±0.3) b
Gondoic acid (C20:1n9) (0.090 ±0.002) a(0.104 ±0.005) b(0.079 ±0.002) c(0.398 ±0.001) d
Behenic acid (C22:0) ND ND ND (0.23 ±0.04)
Lignoceric acid (C24:0) ND ND ND (0.18 ±0.02)
∑SFA (9.55 ±0.09) a(7.8 ±0.1) a(8.82 ±0.02) a(14 ±2) b
∑UFA (90.45 ±0.09) a(92.2 ±0.1) a(91.18 ±0.02) a(86 ±2) b
∑MUFA (54.9 ±0.4) a(52.7 ±0.6) b(74.7 ±0.2) c(50.1 ±0.9) d
∑PUFA (35.5 ±0.3) a(39.5 ±0.5) b(16.5 ±0.2) c(36.2 ±0.9) a
PUFA/SFA ratio (3.7198 ±0.0001) a(5.046 ±0.003) b(1.86 ±0.03) a(2.7 ±0.4) c
Results are the mean of two replicates, expressed in percentages with estimates of standard deviation. Values
on the same row with different letters denote significant differences (p-value < 0.05) among samples according
to ANOVA and Fisher’s LSD test. ND: undetectable. SFA: saturated fatty acids. UFA: unsaturated fatty acids.
MUFA: monounsaturated fatty acids. PUFA: polyunsaturated fatty acids (unsaturation
≥
2). PUFA/SFA: ratio
between polyunsaturated and saturated fatty acids.
On the other hand, the total saturated fatty acid (SFA) and unsaturated fatty acid
(UFA) content of the cherry seed oils differed significantly (p-value < 0.05) with the other
oils studied. All Prunus seed oils were rich in unsaturated fatty acids, which could have
multiple positive health effects. The seed oils had a high content of monounsaturated fatty
acids (MUFA), with oleic acid (48.6–72.7%) being the main component of the oils, which
could exert beneficial effects on the cardiovascular system and on the proper development
and/or functioning of the human brain [
55
]. Seed oils were also characterized based on
their outstanding polyunsaturated fatty acid (PUFA) content (16.5–39.5%), particularly
defined by a high content of linoleic acid (16.4–39.3%), which is essential for a healthy
diet and for cell membrane development [
19
]. However, although the saturated fatty acid
content represented the minority in all oils, a slight increase was observed in cherry seed
oil with a value of 14
±
2%. In the present study, the PUFA/SFA ratio in the seed oils was
especially high (1.86–5.046%), indicating that the oils were healthy, and that they contained
an adequate proportion of healthy fatty acids.
To evaluate the fatty acid content relationships with peach, apricot, plum and cherry
seed oils, a principal component analysis (PCA) was performed. The results of the PCA
analysis are shown in the graph depicted in Figure 1. Two principal components with
eigenvalues greater than or equal to 1 accounted for 92.822% of the total data variability.
The first principal component (PC1) accounted for 64.540% of the total variability and it
was mainly related to margaric acid (C17:0), behenic acid (C22:0), arachidic acid (C20:0),
lignoceric acid (C24:0) and gondoic acid (C20:1n9). The second principal component (PC2)
explained 28.282% of the total variability and it was defined by the strong correlation
with linoleic (C18:2n6c) and
α
-linolenic acid (C18:3n3). The PCA graph indicated the
presence of three homogeneous groups. The first one, formed by peach and apricot seed
oils, was characterized by a high content of unsaturated fatty acids such as palmitoleic
acid (C16:1n7), cis-vaccenic acid (C18:1n7c) and
α
-linolenic acid (C18:3n3). The presence
Molecules 2023,28, 7045 6 of 18
of high linolenic acid content in oils can have multiple health benefits, as this essential
omega-3 (n-3) polyunsaturated fatty acid plays vital roles in proper brain development
and function, cardiovascular health and the anti-inflammatory response [
56
]. In addition,
the presence of high contents of other UFAs such as cis-vaccenic acid and palmitoleic
acid has an anti-inflammatory and protective effect against cardiovascular diseases [
57
,
58
].
The second group consisted of plum seed oil, which was characterized by a high oleic
acid content (C18:1n9c). This type of non-essential fatty acid in the oil can be used in the
treatment and prevention of various disorders, such as autoimmune or cardiovascular
diseases, metabolic disorders and cancer [
55
]. The third and last group consisted of cherry
seed oil, which is characterized by a high SFA content, especially behenic acid (C22:0),
margaric acid (C17:0) and arachidic acid (C20:1n9c).
Molecules 2023, 28, x FOR PEER REVIEW 6 of 19
content represented the minority in all oils, a slight increase was observed in cherry seed
oil with a value of 14 ± 2%. In the present study, the PUFA/SFA ratio in the seed oils was
especially high (1.86–5.046%), indicating that the oils were healthy, and that they con-
tained an adequate proportion of healthy fay acids.
To evaluate the fay acid content relationships with peach, apricot, plum and cherry
seed oils, a principal component analysis (PCA) was performed. The results of the PCA
analysis are shown in the graph depicted in Figure 1. Two principal components with
eigenvalues greater than or equal to 1 accounted for 92.822% of the total data variability.
The first principal component (PC1) accounted for 64.540% of the total variability and it
was mainly related to margaric acid (C17:0), behenic acid (C22:0), arachidic acid (C20:0),
lignoceric acid (C24:0) and gondoic acid (C20:1n9). The second principal component (PC2)
explained 28.282% of the total variability and it was defined by the strong correlation with
linoleic (C18:2n6c) and α-linolenic acid (C18:3n3). The PCA graph indicated the presence
of three homogeneous groups. The first one, formed by peach and apricot seed oils, was
characterized by a high content of unsaturated fay acids such as palmitoleic acid
(C16:1n7), cis-vaccenic acid (C18:1n7c) and α-linolenic acid (C18:3n3). The presence of
high linolenic acid content in oils can have multiple health benefits, as this essential
omega-3 (n-3) polyunsaturated fay acid plays vital roles in proper brain development
and function, cardiovascular health and the anti-inflammatory response [56]. In addition,
the presence of high contents of other UFAs such as cis-vaccenic acid and palmitoleic acid
has an anti-inflammatory and protective effect against cardiovascular diseases [57,58]. The
second group consisted of plum seed oil, which was characterized by a high oleic acid
content (C18:1n9c). This type of non-essential fay acid in the oil can be used in the treat-
ment and prevention of various disorders, such as autoimmune or cardiovascular dis-
eases, metabolic disorders and cancer [55]. The third and last group consisted of cherry
seed oil, which is characterized by a high SFA content, especially behenic acid (C22:0),
margaric acid (C17:0) and arachidic acid (C20:1n9c).
Figure 1. Two−dimensional plot of the principal component analysis (PCA) of the fay
acids present in peach, apricot, plum and cherry seed oils.
Regarding the correlations between the different fay acids presented in the four dif-
ferent oils (Figure 1), it was observed that the UFA, palmitoleic acid (C16:1n7) and cis-
vaccenic acid (C18:1n7c) were highly positively correlated with each other. Palmitoleic
acid was correlated negatively with the saturated fay acids margaric acid (C17:0), be-
henic acid (C22:0) and arachidic acid (C20:0); and the unsaturated fay acid gondoic acid
(C20:1n9). However, cis-vaccenic fay acid was negatively correlated with stearic acid
(C18:0). A high negative correlation was also observed between the two main components
of the oils: linoleic acid (C18:2n6c) and oleic acid (C18:1n9c).
Figure 1.
Two
−
dimensional plot of the principal component analysis (PCA) of the fatty acids present
in peach, apricot, plum and cherry seed oils.
Regarding the correlations between the different fatty acids presented in the four
different oils (Figure 1), it was observed that the UFA, palmitoleic acid (C16:1n7) and cis-
vaccenic acid (C18:1n7c) were highly positively correlated with each other. Palmitoleic acid
was correlated negatively with the saturated fatty acids margaric acid (C17:0), behenic acid
(C22:0) and arachidic acid (C20:0); and the unsaturated fatty acid gondoic acid (C20:1n9).
However, cis-vaccenic fatty acid was negatively correlated with stearic acid (C18:0). A
high negative correlation was also observed between the two main components of the oils:
linoleic acid (C18:2n6c) and oleic acid (C18:1n9c).
2.2.3. Lipid Health Quality Indexes
The atherogenicity index (AI) showed two homogeneous groups (p-value < 0.05): on
the one hand, peach and cherry seed oil were grouped together, and on the other, apricot
and plum seed oil were grouped together. All oils showed low values of this index, where
the lowest value was found in plum seed oil (0.0626) and the highest in cherry seed oil
(0.09). The results corresponding to the thrombogenicity (TI) index showed that peach,
apricot and plum seed oils were statistically similar (p-value
≥
0.05), while cherry seed oil
differed from them. The lowest value corresponded to the apricot kernel oil (0.166) and the
highest to the cherry kernel oil (0.28). According to the literature [
23
,
24
,
59
], low values of
both the AI and TI are related to the prevention of coronary heart disease. Thus, the lower
these values, the healthier the food, indicating the promising potential of these seed oils.
According to the desirable fatty acid (DFA) index, three statistically homogeneous
groups were found (peach and apricot oil, apricot and plum oil and, lastly, cherry oil).
High values (90–94) were observed for all four Prunus seed oils (Table 4), evidencing their
high hypocholesterolaemic properties. The hypocholesterolemic/hypercholesterolemic
(H/H) ratio correlates with the DFA index and measures the bioactive properties of oils to
lower blood cholesterol levels [
60
]. In this case, the oils were grouped into two statistically
homogeneous groups and showed high values for this nutritional index (11.3–15.83).
Molecules 2023,28, 7045 7 of 18
Table 4. Indexes of the nutritional quality of peach, apricot, plum and cherry seed oils.
Lipid Indexes Peach Oil Apricot Oil Plum Oil Cherry Oil
Desirable fatty acid (DFA) (91.85 ±0.09) a(93.44 ±0.5) a,b (94.05 ±0.03) b(90 ±1) c
Atherogenicity (AI) (0.088 ±0.001) a(0.0691 ±0.0004) b(0.0626 ±0.0003) b(0.09 ±0.01) a
Thrombogenicity (TI) (0.207 ±0.002) a(0.166 ±0.002) a(0.188 ±0.001) a(0.28 ±0.04) b
Hypocholesterolemic/
Hypercholesterolemic (H/H) (11.3 ±0.1) a(14.29 ±0.08) b(15.83 ±0.06) b(11 ±1) a
n6/n3 fatty acid ratio (275 ±10) a(228 ±8) b(201.5 ±0.6) c(339 ±9) d
Values are expressed as mean
±
standard deviation (n = 2). Values with different letters in the same row denote
significant differences (p-value < 0.05) among samples according to ANOVA and Fisher ’s LSD test. n-6/n-3: ratio
between omega-6 and omega-3 fatty acids.
On the other hand, all seed oils were shown to have a higher proportion of omega-6
fatty acids than omega-3 fatty acids (Table 4). The oils presented significant differences
among them (p-value < 0.05), with the lowest value found in plum seed oil (201.5
±
0.6).
Although these values suggest a health risk, the presence of high amounts of linoleic acid
is required by the human body for the maintenance of cell membranes, brain function and
the transmission of nervous impulses in normal conditions and the correct oxygenation of
the blood [61]. Therefore, a balanced omega-6/omega-3 ratio diet is needed.
Considering all the nutritional lipid indexes (AI, TI, H/H, DFA, n6/n3 ratio) used
to evaluate the quality of the oils, plum seed oil was the one that presented the best
nutritional quality. However, all Prunus seed oils could play beneficial roles in human
health, particularly in the prevention and/or treatment of coronary and cardiovascular
diseases and obesity [
62
,
63
]. Due to the interesting nutritional characteristics of Prunus
seed oils, they could be used in the food and/or nutraceutical industries as natural food
supplements or additives [37,39].
2.2.4. Antioxidant Activity
The determination of the oil antioxidant activity is another parameter that is used to
evaluate the quality of oils, since this bioactive property correlates with the lipid composi-
tion and the presence of natural antioxidants in the oil [
64
]. Table 5shows the antioxidant
activity of peach, apricot, plum and cherry seed oils (expressed as mg
·
mL
−1
of oil). Trolox
was used as a standard and its IC
50
was 0.0025
±
0.0001 mg
·
mL
−1
. All studied oils showed
high values of IC
50
, ranging from 20 to 35 mg
·
mL
−1
, with respect to the Trolox standard.
Furthermore, the IC
50
values obtained for Prunus seed oils were higher than those reported
by Fratianni et al. [
38
], indicating the interesting potential of the oils obtained from the
agri-food waste. Apricot and plum oils were those with the highest antioxidant capacity
(IC
50
= 20–21 mg
·
mL
−1
), compared to peach and cherry oils, which were characterized by
a significantly lower (p-value < 0.05) antioxidant capacity (IC50 = 31–35 mg·mL−1).
Table 5.
Antioxidant activity determined after 24 h storage of peach, apricot, plum and cherry
kernel oils.
Oils DPPH
IC50 (mg·mL−1of Oil)
Peach oil (31 ±3) a
Apricot oil (21.2 ±0.9) b
Plum oil (20 ±3) b
Cherry oil (35 ±4) a
Values are expressed as mean
±
standard deviation (n = 2). Values with different letters denote significant
differences (p-value < 0.05) among samples according to ANOVA and Fisher ’s LSD test. IC
50
values are the
concentration of sample required to scavenge 50% of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical.
To establish the possible relationship between the fatty acid composition (Table 3)
and the antioxidant capacity of seed oils, a Pearson correlation analysis was carried out
Molecules 2023,28, 7045 8 of 18
(Figure 2). The correlation coefficients ranges from
−
1 to +1 to express the linear relationship
between the different study factors. The correlation analysis showed that the main fatty
acids affecting the oils’ antioxidant capacity (IC
50
value) were palmitic acid (C16:0) and
palmitoleic acid (C16:1n7). A high positive correlation was also observed between the
content of palmitic acid and the IC
50
value (r = 0.97). A higher content of palmitic acid
in the oil led to an increase in the IC
50
value and, therefore, a decrease in the antioxidant
capacity. Palmitic acid is associated with increasing total cholesterol levels in plasma [
38
];
however, it was found in low proportions in oils (5.71–8.1%). Conversely, a high negative
correlation was observed between the IC
50
value and the palmitoleic acid (C16:1n7) content
(r =
−
0.89), indicating that the high content of this type of UFA in the oils contributes
positively to the antioxidant capacity (lowest IC
50
value) and acts beneficially in the human
body, protecting against oxidative stress [55].
Molecules 2023, 28, x FOR PEER REVIEW 8 of 19
high values of IC50, ranging from 20 to 35 mg·mL−1, with respect to the Trolox standard.
Furthermore, the IC50 values obtained for Prunus seed oils were higher than those reported
by Fratianni et al. [38], indicating the interesting potential of the oils obtained from the
agri-food waste. Apricot and plum oils were those with the highest antioxidant capacity
(IC50 = 20–21 mg·mL−1), compared to peach and cherry oils, which were characterized by
a significantly lower (p-value < 0.05) antioxidant capacity (IC50 = 31–35 mg·mL−1).
Table 5. Antioxidant activity determined after 24 h storage of peach, apricot, plum and cherry kernel
oils.
Oils DPPH
IC50 (mg·mL−1 of Oil)
Peach oil (31 ± 3) a
Apricot oil (21.2 ± 0.9) b
Plum oil (20 ± 3) b
Cherry oil (35 ± 4) a
Values are expressed as mean ± standard deviation (n = 2). Values with different leers denote sig-
nificant differences (p-value < 0.05) among samples according to ANOVA and Fisher’s LSD test. IC50
values are the concentration of sample required to scavenge 50% of 2,2-diphenyl-1-picrylhydrazyl
(DPPH) free radical.
To establish the possible relationship between the fay acid composition (Table 3)
and the antioxidant capacity of seed oils, a Pearson correlation analysis was carried out
(Figure 2). The correlation coefficients ranges from −1 to +1 to express the linear relation-
ship between the different study factors. The correlation analysis showed that the main
fay acids affecting the oils’ antioxidant capacity (IC50 value) were palmitic acid (C16:0)
and palmitoleic acid (C16:1n7). A high positive correlation was also observed between the
content of palmitic acid and the IC50 value (r = 0.97). A higher content of palmitic acid in
the oil led to an increase in the IC50 value and, therefore, a decrease in the antioxidant
capacity. Palmitic acid is associated with increasing total cholesterol levels in plasma [38];
however, it was found in low proportions in oils (5.71–8.1%). Conversely, a high negative
correlation was observed between the IC50 value and the palmitoleic acid (C16:1n7) con-
tent (r = −0.89), indicating that the high content of this type of UFA in the oils contributes
positively to the antioxidant capacity (lowest IC50 value) and acts beneficially in the human
body, protecting against oxidative stress [55].
Figure 2. Pearson correlation heat map between fay acid contents and antioxidant activity of
Prunus seed oils. IC50 values mean the concentration of sample required to scavenge 50% of DPPH
free radical.
Figure 2.
Pearson correlation heat map between fatty acid contents and antioxidant activity of
Prunus seed oils. IC
50
values mean the concentration of sample required to scavenge 50% of DPPH
free radical.
2.3. Comparative Study of the Oxidative Stability of Seed Oils
Lipid oxidation is one of the biggest problems affecting oil quality. Therefore, the
study of the oxidative stability is required.
The oil oxidative stability was measured over a period of 1–22 days using the 2,2-
diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging method. The results obtained
are shown in Table 6.
Table 6.
Variation in the antioxidant capacity of peach, apricot, plum and cherry seed oils with
storage time.
Storage Time (h) IC50 Peach Oil
(mg·mL−1of Oil)
IC50 Apricot Oil
(mg·mL−1of Oil)
IC50 Plum Oil
(mg·mL−1of Oil)
IC50 Cherry Oil
(mg·mL−1of Oil)
24 (1 day) (31 ±3) a(21.2 ±0.9) a(20 ±3) a(35 ±4) a
48 (2 days) (37 ±1) bn.m. (21.9 ±0.7) a,b n.m.
72 (3 days) n.m. (28.7 ±0.5) bn.m. (41.6 ±0.2) a,b
120 (5 days) (37.8 ±0.6) bn.m. n.m. n.m.
168 (7 days) n.m. n.m. (25 ±1) bn.m.
240 (10 days) (39 ±3) c(57 ±1) cn.m. (46 ±1) b,c
360 (15 days) n.m. n.m. (26 ±3) b(51 ±4) c
528 (22 days) n.m. n.m. (26.2 ±0.3) bn.m.
Values are expressed as mean
±
standard deviation (n = 2). IC
50
values mean the concentration of sample required
to scavenge 50% of DPPH free radical and n.m. signifies not measured on that specific storage time. For each type
of oil, values with different letters in the same column denote significant differences (p-value < 0.05) between
storage times according to ANOVA and Fisher’s LSD test.
Molecules 2023,28, 7045 9 of 18
To evaluate the trend of the oxidative stability, IC
50
values were plotted versus storage
time (Figure 3). The curves shown in Figure 3were non-linear and fitted adequately to
a logarithmic model (with correlation coefficients (R
2
) between 0.8547 and 0.9727). Thus,
the variation in antioxidant capacity during storage time followed a logarithmic model of
the first-order degradation kinetic reaction [
35
,
65
]. In the logarithmic curve of plum oil,
an apparently constant trend was observed between the IC
50
values and the storage times,
indicating its high stability against lipid oxidation. However, in apricot, peach and cherry
seed oils, an increasing trend of the IC
50
value was observed at 240 h (22 days) of storage
time, which indicated that the lipid oxidation phenomenon had occurred.
Molecules 2023, 28, x FOR PEER REVIEW 9 of 19
2.3. Comparative Study of the Oxidative Stability of Seed Oils
Lipid oxidation is one of the biggest problems affecting oil quality. Therefore, the
study of the oxidative stability is required.
The oil oxidative stability was measured over a period of 1–22 days using the 2,2-
diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging method. The results obtained
are shown in Table 6.
Table 6. Variation in the antioxidant capacity of peach, apricot, plum and cherry seed oils with stor-
age time.
Storage Time (h) IC50 Peach Oil
(mg·mL−1 of Oil)
IC50 Apricot Oil
(mg·mL−1 of Oil)
IC50 Plum Oil
(mg·mL−1 of Oil)
IC50 Cherry Oil
(mg·mL−1 of Oil)
24 (1 day) (31 ± 3) a (21.2 ± 0.9) a (20 ± 3) a (35 ± 4) a
48 (2 days) (37 ± 1) b n.m. (21.9 ± 0.7) a,b n.m.
72 (3 days) n.m. (28.7 ± 0.5) b n.m. (41.6 ± 0.2) a,b
120 (5 days) (37.8 ± 0.6) b n.m. n.m. n.m.
168 (7 days) n.m. n.m. (25 ± 1) b n.m.
240 (10 days) (39 ± 3) c (57 ± 1) c n.m. (46 ± 1) b,c
360 (15 days) n.m. n.m. (26 ± 3) b (51 ± 4) c
528 (22 days) n.m. n.m. (26.2 ± 0.3) b n.m.
Values are expressed as mean ± standard deviation (n = 2). IC50 values mean the concentration of
sample required to scavenge 50% of DPPH free radical and n.m. signifies not measured on that
specific storage time. For each type of oil, values with different leers in the same column denote
significant differences (p-value < 0.05) between storage times according to ANOVA and Fisher’s LSD
test.
To evaluate the trend of the oxidative stability, IC50 values were ploed versus stor-
age time (Figure 3). The curves shown in Figure 3 were non-linear and fied adequately
to a logarithmic model (with correlation coefficients (R2) between 0.8547 and 0.9727). Thus,
the variation in antioxidant capacity during storage time followed a logarithmic model of
the first-order degradation kinetic reaction [35,65]. In the logarithmic curve of plum oil,
an apparently constant trend was observed between the IC50 values and the storage times,
indicating its high stability against lipid oxidation. However, in apricot, peach and cherry
seed oils, an increasing trend of the IC50 value was observed at 240 h (22 days) of storage
time, which indicated that the lipid oxidation phenomenon had occurred.
Figure 3. Kinetics curves of logarithmic model of IC50 values versus storage time of peach, apricot,
plum and cherry seed oils.
Figure 3.
Kinetics curves of logarithmic model of IC
50
values versus storage time of peach, apricot,
plum and cherry seed oils.
To determine the time at which the oil was stable against the oxidation of its fatty
acids the t
1/2
value was estimated, which refers to the time at which the concentration
of oil antioxidants is reduced by half. For this purpose, the IC
100
was calculated as the
sample concentration required to remove 100% of the free radical DPPH. From this value,
ln(100-IC
100
) (ln
c.antioxidants
) was calculated and plotted against storage time, following the
first-order linear kinetic equation (ln
c.antioxidants
= ln
C0 −
kt). The data related to the linear
fit (intercept, slope and correlation coefficient (R2)) are given in Table 7.
Table 7.
Parameters of the linear fit (intercept, slope, correlation coefficient (R
2
)) of ln
c.antioxidants
versus storage time of peach, apricot, plum and cherry kernel oils.
Prunus Seed Oil Intercept
(mg·mL−1)
Slope
(h−1)t1/2 (h) R2
Peach (−0.012 ±0.003) (4.0 ±0.4) 58 (2 days) 0.90
Apricot (−0.006 ±0.001) (4.2±0.1) 110 (4 days) 1.00
Plum (−0.0004 ±0.0001) (4.0 ±0.3) 1732 (72 days) 0.78
Cherry (−0.0057 ±0.0001) (3.4 ±0.2) 121 (5 days) 0.94
The intercept refers to the logarithm of the initial concentration of antioxidant compounds (ln
C0
) and the slope to
the first-order constant (k). A linear trend in the data was observed in all oils.
It was observed that the oxidative stability of all oils conformed to first-order kinetics
with high correlation factors (R
2
) ranging from 0.78 to 1.00. The times at which the an-
tioxidant concentration halved were different for each oil. On the one hand, the longest
time and, thus, the highest stability against lipid oxidation, was observed for the plum oil
(
t1/2 = 1732 h
(72 days)). On the other hand, peach oil showed the shortest stability time
(t
1/2
= 58 h (2 days)). Apricot kernel oil and cherry oil showed t
1/2
values of 110 and 121 h
(4 and 5 days), respectively.
Molecules 2023,28, 7045 10 of 18
The results obtained according to literature data [
32
,
61
] evidenced that the oil composi-
tion strongly affects its antioxidant activity and oxidative stability. Consequently, the effect
of fatty acids on oil oxidative stability was studied using principal component analysis
based on the stability time data reported in Table 7and the data concerning fatty acid
composition (Table 3). Two principal components, with eigenvalues greater than or equal
to 1, were extracted. They accounted for 93.213% of the total data variability (Figure 4).
Molecules 2023, 28, x FOR PEER REVIEW 10 of 19
To determine the time at which the oil was stable against the oxidation of its fay
acids the t1/2 value was estimated, which refers to the time at which the concentration of
oil antioxidants is reduced by half. For this purpose, the IC100 was calculated as the sample
concentration required to remove 100% of the free radical DPPH. From this value, ln(100-
IC100) (lnc.antioxidants) was calculated and ploed against storage time, following the first-or-
der linear kinetic equation (lnc.antioxidants = lnC0 − kt). The data related to the linear fit (inter-
cept, slope and correlation coefficient (R2)) are given in Table 7.
Table 7. Parameters of the linear fit (intercept, slope, correlation coefficient (R2)) of lnc.antioxidants versus
storage time of peach, apricot, plum and cherry kernel oils.
Prunus Seed Oil Intercept
(mg·mL−1)
Slope
(h−1) t1/2 (h) R2
Peach (−0.012 ± 0.003) (4.0 ± 0.4) 58 (2 days) 0.90
Apricot (−0.006 ± 0.001) (4.2± 0.1) 110 (4 days) 1.00
Plum (−0.0004 ± 0.0001) (4.0 ± 0.3) 1732 (72 days) 0.78
Cherry (−0.0057 ± 0.0001) (3.4 ± 0.2) 121 (5 days) 0.94
The intercept refers to the logarithm of the initial concentration of antioxidant compounds (lnC0) and
the slope to the first-order constant (k). A linear trend in the data was observed in all oils.
It was observed that the oxidative stability of all oils conformed to first-order kinetics
with high correlation factors (R2) ranging from 0.78 to 1.00. The times at which the antiox-
idant concentration halved were different for each oil. On the one hand, the longest time
and, thus, the highest stability against lipid oxidation, was observed for the plum oil (t1/2
= 1732 h (72 days)). On the other hand, peach oil showed the shortest stability time (t1/2 =
58 h (2 days)). Apricot kernel oil and cherry oil showed t1/2 values of 110 and 121 h (4 and
5 days), respectively.
The results obtained according to literature data [32,61] evidenced that the oil com-
position strongly affects its antioxidant activity and oxidative stability. Consequently, the
effect of fay acids on oil oxidative stability was studied using principal component anal-
ysis based on the stability time data reported in Table 7 and the data concerning fay acid
composition (Table 3). Two principal components, with eigenvalues greater than or equal
to 1, were extracted. They accounted for 93.213% of the total data variability (Figure 4).
Figure 4. Two-dimensional principal component analysis (PCA) plot of fay acid content, antioxi-
dant activity (IC50) and oxidative stability of peach, apricot, plum and cherry seed oils.
The first principal component (PC1) represented 60.401% of the total data variability
and it was mainly related to margaric acid (C17:0), behenic acid (C22:0), arachidic acid
(C20:0), lignoceric acid (C24:0) and gondoic acid (C20:1n9). The second principal compo-
nent (PC2) explained 32.813% of the total data variability and it was defined by the strong
correlation with both linoleic (C18:2n6c) and α-linolenic acids (C18:3n3). In the PCA graph
Figure 4.
Two-dimensional principal component analysis (PCA) plot of fatty acid content, antioxidant
activity (IC50) and oxidative stability of peach, apricot, plum and cherry seed oils.
The first principal component (PC1) represented 60.401% of the total data variability
and it was mainly related to margaric acid (C17:0), behenic acid (C22:0), arachidic acid
(C20:0), lignoceric acid (C24:0) and gondoic acid (C20:1n9). The second principal component
(PC2) explained 32.813% of the total data variability and it was defined by the strong
correlation with both linoleic (C18:2n6c) and
α
-linolenic acids (C18:3n3). In the PCA graph
depicted in Figure 4, a high positive correlation was also observed between the oxidative
stability and the oleic acid content. On the contrary, the maximum negative correlation was
observed between the oxidative stability and the content of linoleic acid. Similarly, Nederal
et al. [
66
] observed that the oxidative stability of cold-pressed pumpkin oils was positively
correlated with the oleic acid content and negatively correlated with the linoleic and
α
-
linolenic acid contents. This fact could be explained by the presence of consecutive double
bonds, which are more susceptible to attack by the oxygen present in the environment.
Furthermore, it was observed that plum seed oil had the greatest stability against the
oxidation of fatty acids due to its high content of oleic monounsaturated fatty acid.
The adequate antioxidant activity and oxidative stability of Prunus seed oils opens
new fields of application in the cosmetic industry for their use as active ingredients in
antioxidant cosmetics [39].
3. Materials and Methods
3.1. Reagents and Solvents
Analytical grade reagents were required in the procedures. n-Hexane (96%) and
methanol (MeOH,
≥
99%) for HPLC gradient quality were supplied by Scharlab (Barcelona,
Spain). Sodium hydroxide pellets (NaOH) (98%), sulphuric acid (H
2
SO
4
, 98%), boric acid
(
≥
99%) and methylene blue (82%) were obtained from Panreac (Barcelona, Spain). Dimethyl
sulfoxide (DMSO,
≥
99.9%) and 2,2-diphenyl-1-picrylhydrazyl (DPPH,
≥
99.9%) were pro-
vided by Sigma-Aldrich (St. Louis, MO, USA). Methyl red, Kjeldahl catalyst tables and
distilled water system were purchased from Merck (Madrid, Spain). Fatty acid standards
FAME 37 component SUPELCO Ref CRM47885, PUFA No. 3 Menhaden oil Ref 47085-U
and tridecanoic acid (C13:0,
≥
99%) were purchased from Sigma-Aldrich (Barcelona, Spain).
The standard Trolox was provided by Sigma-Aldrich (Burghasen, Germany).
Molecules 2023,28, 7045 11 of 18
3.2. Sample Preparation
Plum (Prunus domestica) and cherry (Prunus avium) pits were purchased from The Jerte
Valley Cooperatives Group (Cáceres, Spain). Peach pits (Prunus persica) and apricot pits
and seeds (Prunus armeniaca) were purchased from The Agri-Food Cooperatives of Castilla
La Mancha (Hellín, Albacete).
Prior to any treatment, fresh samples, received during the campaign period corre-
sponding to the year 2022, were air-dried at 40
◦
C (Digitheat oven, J.P Selecta
®
, Abrera,
Barcelona, Spain) for 24 h, and then stored at room temperature until use.
For compositional analysis, the stones of the Prunus fruits studied were separated
manually, using a hammer, into shell and seed. The seeds were then crushed in an ultra-
centrifugal grinder (Retsh
™
ZM200, Haan, Alemania) and sieved with a stainless-steel
sieve to particle sizes below 1 mm. Seed samples were stored in clear plastic zip-lock bags
until analysis.
3.3. Nutritional Analysis of the Four Types of Fruit Seed of Prunus Family
3.3.1. Determination of Seed-to-Whole Stone Ratio
The percentage in weight of seeds in relation to the stone was determined by weighing
25 stones and their respective seeds on a 0.0001 g precision digital analytical balance (Precisa
Series 290, Dietikon, Switzerland) for each of the Prunus varieties.
3.3.2. Determination of Moisture Content
The moisture content of the seeds was determined according to the standard procedure
AOAC 925.10 [
67
], with slight modifications. Approximately 2 g of seed sample was
weighed on a dried crucible and introduced in an oven at 105
◦
C for 2 h and 30 min until a
constant weight was obtained. After cooling, the crucible was weighed again and the free
water content was calculated as sample weight loss and expressed as a percentage. It was
determined as percentage in weight (mean ±standard deviation, n = 3).
3.3.3. Determination of Ash Content
For the determination of ash, AOAC 923.03 standard procedure was followed [
68
].
Briefly, a sample amount of 2 g was weighed on a clean and dry crucible, which was then
placed in muffle furnace (J.P Selecta
®
, Abrera, Barcelona, Spain) at 550
◦
C for 4 h. The
appearances of grey/white ash indicated the complete oxidation of all organic matter in
the sample. Then, the crucible with the ash was cooled in the desiccator and weighed on a
precision digital analytical balance (Precisa Series 290, Dietikon, Switzerland) until reaching
a constant weight. Finally, the ash content was then calculated as a percentage in weight of
dried sample and expressed as mean ±standard deviation (n = 3).
3.3.4. Determination of Fat Content
The total oil content in the samples was determined following an AOAC 960.39
procedure [
69
]. First, a Soxhelt extraction was carried out by placing 15 g of seed with
a particle size of less than 1 mm into a cellulose cartridge (FILTER-LAB
®
, Darmstadt,
Germany), within a collecting flask of 250 mL capacity (Mervilab S.A., Madrid, Spain)
that was previously dried in an oven (Digitheat, J.P Selecta
®
, Abrera, Barcelona, Spain) at
105
◦
C for 2 h and weighed. The cellulose cartridge was inserted into the Soxhlet extractor
body and 150 mL of n-hexane (seed-solvent ratio 1:10 (w/v)) was added to the collecting
flask. Prunus seeds were then extracted under reflux at 69
◦
C for 6 h (6–8 cycles/h). Then,
the solvent was removed using a rotary evaporator (Buchi
™
Rotavapor
™
R-100, Fisher
Scientific, Hampton, VA, USA) at 69
◦
C, and the collecting flask with the extract was placed
in a vacuum oven (Vaciotem-TV, digital, J.P Selecta
®
, Abrera, Barcelona, Spain) at 40
◦
C for
24 h. Finally, it was cooled in a desiccator for 30 min and weighed again. This procedure
was carried out in triplicate. The oils were stored in airtight amber-colored glass bottles
and kept at 4
◦
C prior to analysis. The percentage of fat was expressed as mean
±
standard
deviation (n = 3) on a dry basis.
Molecules 2023,28, 7045 12 of 18
3.3.5. Determination of Crude Fiber Content
The content of crude fiber in the different seed samples was assessed according to
an official methodology described elsewhere [
70
]. For this purpose, approximately 2 g
of defatted seed was weighed on a precision digital analytical balance and subjected to a
boiling step for 30 min with 200 mL of 0.128 M H
2
SO
4
solution. Then, the solution was
filtered through a cotton filter to drain the acid and the solid residue was washed with hot
distilled water and subjected to a further boiling for 30 min with 200 mL of 0.313 M NaOH
solution. Following filtration through a cotton filter, the insoluble residue was dried in
an oven (Digitheat, J.P Selecta
®
, Abrera, Barcelona, Spain) at 230
◦
C for 2 h and weighed,
and subsequently placed in a muffle furnace (J.P Selecta
®
, Abrera, Barcelona, Spain) at
550
◦
C for 2 h. Finally, the crucible with the samples was cooled in the desiccator and
weighed again. The crude fiber content was determined using the quotient of the difference
in weight of the dry insoluble residue and the incinerated residue between the total mass
of the dry seed. This test was performed in triplicate and expressed as mean
±
standard
deviation.
3.3.6. Determination of Protein Nitrogen Content
The protein content of the seed samples was determined using the Kjeldahl method [
71
].
Approximately 1 g of dried sample was added in digestion flask with 12 mL of concentrated
H
2
SO
4
and one Kjeldahl catalyst tablet (Merck, Darmstadt, Germany). The mixture was
placed in the digestion module (VELP Scientifica, Usmate, Italy) at 410
◦
C for 1 h. After
cooling, the digested mixture was placed in the steam distillation module (VELP Scientifica,
Usmate, Italy) with 50 mL of 2% (w) boric acid, two drops of methyl red and one drop
of methylene blue. The system was programmed to add 18 mL of 40% (w) NaOH in 12 s
and the distillation process took place for 210 s. Finally, the distilled ammonia collective
in the boric acid solution was titrated with 0.03 M H
2
SO
4
solution until it turned green
to violet. The procedure was carried out in triplicate and two blanks were also prepared.
Finally, the protein content was estimated from the percentage of nitrogen using Equation
(1), where the coefficient of 6.25 is the correction factor for this type of sample and “%N” is
the percentage of nitrogen in the sample; and Equation (2) where “s” is the sample titration
reading, “b” is the blank titration reading, “M” is the molarity of H
2
SO
4
and “0.014” the
milli equivalent weight of nitrogen.
Proteinnitrogen(%)=6.25 ×%N (1)
N(%) = (s−b)×0.014 ×M
wtsample (2)
3.3.7. Determination of Total Carbohydrates
The carbohydrate content in Prunus seeds, expressed as the mean value of the weight
percentage
±
standard deviation (n = 3), was calculated by subtracting the sum of the
percentage of moisture, ash, fat and protein nitrogen contents from 100% according to
Ayoola et al. [72].
3.4. Physico-Chemical Characterization of Prunus Seed Oils
3.4.1. Determination of Oil Density
The density of oils was determined using a density meter (Anton Paar DMA 5000,
Madrid, Spain) with an operative temperature of 25
◦
C. The tests were carried out in
triplicate for each sample.
3.4.2. Determination of Fatty Acid Profile
The determination of fatty acid composition in the extracted oils was carried out using
gas chromatography coupled to a FID detector (Agilent Technologies, 7820A, Santa Clara,
Molecules 2023,28, 7045 13 of 18
CA, USA), following the internal derivatization procedure to methyl esters proposed by
Lee et al. [
51
]. Prior to the chromatographic analysis, the extracted oils (200 mg approxi-
mately) were freeze-dried (Sp Scientific, Warminster, PA, USA) at
−
50
◦
C and 150 mbar
for 72 h. To synthesize fatty acid methyl esters (FAME), the fatty acids were incubated
with 0.5 M sodium methoxide at 60
◦
C for 15 min, followed by extraction with acetyl
chloride in methanol 1:10 (v/v) and incubation at 60
◦
C for 60 min. One milliliter of purified
water, 1.5 mL of hexane and sodium sulphate was added to each sample, followed by a
centrifugation step (4
◦
C, 1500 rpm for 5 min). One milliliter of the supernatant was used
for subsequent analyses. Samples were evaporated in a Savant
™
SPD131DDA SpeedVac
™
concentrator (Thermo Fisher Scientific, Madrid, Spain) and resuspended in hexane (Thermo
Fisher Scientific, Madrid, Spain) The chromatographic separation was achieved using a
capillary chromatographic column (60 m
×
250
µ
m
×
0.25
µ
m) (Agilent Technologies DB-23
Ref 122-2362), helium as a carrier gas at 1 mL
·
min
−1
flow rate and split injection mode
(40:1). The detector temperature was set at 260
◦
C and the injector furnace temperature
at 250
◦
C. The oven temperature gradient started at 100
◦
C for 2 min, after which the
temperature increased by 8
◦
C/min to 145
◦
C. This condition was maintained for 20 min
and then rose by 5
◦
C/min to 230
◦
C. Chromatograms were recorded and analyzed using
EZChrom Elite compact 3.3.2. software (Agilent Technologies, Madrid, Spain).
The identification of the fatty acids was performed by comparing the retention
time of the samples with that of the commercial standards (FAME 37 SUPELCO Ref
CRM47885 + PUFA No. 3 Menhaden oil Ref 47085-U). For quantification, an internal
standard calibration of response factors (RF) was performed as a way to correlate the ratio
of areas between each FAME and the internal standard with the FAME concentration, using
tridecanoic acid (C13:0) as internal standard (1 mg was added before methylation). To
determine the relative amounts of each FAME present in the different samples, a response
factor of 1 was set and the composition was expressed as a percentage (%) considering the
individual area of each FAME and the total area (considering that 100% corresponds to the
sum of all the areas of the determined analytes). Analyses were performed in duplicate.
3.4.3. Lipid Nutritional Quality Indexes
To estimate the nutritional value of the seed oils studied the total content of saturated
(SFA), unsaturated (UFA), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty
acids, along with the lipid nutritional quality indexes related to the fatty acid profile
and healthy fat consumption (the atherogenicity index (AI), thrombogenicity index (TI),
hypocholesterolemic-hypercholesterolemic ratio (H/H) and desirable fatty acid (DFA)
index) were calculated as defined elsewhere [24,25]:
∑SFA =C16 : 0 +C17 : 0+C18 : 0 +C20 : 0 +C22 : 0 +C24 : 0 (3)
∑UFA =∑MUFA +∑PUFA (4)
∑MUFA =C16 : 1n7 +C18 : 1n7c+C18 : 1n9c (5)
∑PUFA =C18 : 2n6c +C18 : 3n3+C20 : 1n9 (6)
DFA =∑MUFA +∑PUFA +C18 : 0 (7)
AI =C12 : 0 +4(C14 : 0)+C16 : 0
∑MUFA +∑PUFA (8)
H/H =C18 : 1 +∑PUFA
C14 : 0 +C16 : 0 (9)
Molecules 2023,28, 7045 14 of 18
TI =C12 : 0 +C16 : 0+C18 : 0
(0.5 ∑MUFA)+(0.5 ×n6 ∑PUFA)+(3×n3 ∑PUFA)×n3 ∑PUFA
n6 ∑PUFA (10)
where n3
∑
PUFA stands for the sum of omega-3 polyunsaturated fatty acids, n6
∑
PUFA
is the sum of omega-6 polyunsaturated fatty acids, C16:0 corresponds to palmitic acid,
C16:1n7 is palmitoleic acid, C17:0 is margaric acid, C18:0 is stearic acid, C18:1n7c is cis-
vaccenic acid, C18:1n9c is oleic acid, C18:2n6c is linoleic acid, C18:3n3 is
α
-linolenic acid,
C20:0 is arachidic acid, C20:1n9 is 11-eicosenoic acid, C22:0 is behenic acid and C24:0 is
lignoceric acid.
Finally, the n6/n3 fatty acid ratio, which is related to a healthy diet, was calculated
according to the equation proposed by Asha et al. [73].
3.4.4. Determination of the Antioxidant Capacity of Seed Oils
The antioxidant activity of Prunus seed oils was measured as DPPH free-radical
scavenging capacity, following the methodology proposed by Fratianni et al. [
38
], which
was slightly modified. Briefly, 30
µ
L of eight methanolic working solutions (0–30
µ
L)
prepared using dilution from oil solutions (448–850 mg
·
mL
−1
, DMSO) were mixed with
270
µ
L of 6
×
10
−5
M DPPH methanolic solution in 96-well microplate. The final solutions
were stored in the dark at room temperature and under shaking (300 rpm) for 60 min.
The absorbance was then measured at 515 nm using a Thermo Scientific Multiskan GO
spectrophotometer. Finally, the oil concentrations were plotted against DPPH remaining
percentages and the results were expressed as IC
50
values, i.e., the concentration of sample
required to inhibit 50% the initial DPPH concentration. The assay was performed in
duplicate and Trolox standard was used as positive control.
3.4.5. Evaluation of the Antioxidant Stability of Seed Oils
The antioxidant activity of Prunus seed oils was monitored for 22 days to determine the
oxidative stability of the evaluated oils using the DPPH method described in Section 3.4.4.
For this purpose, the IC
100
, i.e., the minimum oil concentration that completely reduced
the initial DPPH absorbance at 515 nm, was determined over the storage time (24 h and
22 days). The former was estimated as the initial concentration of antioxidant agents
present in the oils and the data obtained were fitted to first-order kinetics, according to
Equation (11), where “ln
c.antioxidants
” is the logarithm of the antioxidants present in the oils
during storage time, “ln
C0”
is the logarithm of IC
100
value, “k” is the velocity constant and
“t” corresponds to the storage time.
Thus, from the logarithmic calibration fits, the mean degradation time, known as the
time in which the initial concentration of antioxidants is halved, was calculated for the
different Prunus seed oils.
lnc.antioxidants =lnC0 −kt (11)
3.5. Statistical Analysis
Statistical analysis was performed using the Statgraphics 19 software package (Stat-
graphics Technologies Inc., Rockville, MD, USA). Data were statistically analyzed using
multivariate and univariate analysis of variance (ANOVA), principal component analysis
(PCA) and Pearson correlation analysis. Significant differences between determinations
were evaluated using Fisher’s least significant difference (LSD) test at 95% confidence level
(p-value < 0.05).
4. Conclusions
This study focuses on the valorization of peach, apricot, plum and cherry seed agri-
food waste based on the extraction of seed oil and its characterization in terms of fatty acid
content, antioxidant activity and oxidative stability.
Molecules 2023,28, 7045 15 of 18
Prunus seeds presented high added value due to their remarkable fat (30–38%, w),
crude fiber (7–24%, w), protein (10–35%, w) and carbohydrate (13–25%, w) contents. The
main components of interest of the seeds were the seed oils. The high content of unsatu-
rated fatty acids in the oils, such as oleic (48.6–72.7%) and linoleic acid (16.4–39.3%), and
their adequate heart-healthy indexes make their potential use in the food and nutraceutical
industry feasible, either as food supplements or nutraceuticals. In addition, the outstand-
ing antioxidant activity (IC
50
= 30–35 mg
·
mL
−1
) and the high oxidative stability during
1–22 days
of storage of the oils, especially the plum seed oil, opens new applications in the
cosmetic industry as an active ingredient in antioxidant cosmetics.
Supplementary Materials:
The following supporting information can be downloaded at:
https://www.mdpi.com/article/10.3390/molecules28207045/s1, Figure S1: Chromatogram of the
standard mixture FAME 37 component SUPELCO Ref CRM47885 using GC-FID; Figure S2: Chro-
matogram of the standard mixture PUFA No. 3 Menhaden oil Ref 47085-U using GC-FID; Figure S3:
Chromatogram of plum seed oil using GC-FID and Figure S4: Chromatogram of cherry seed oil using
GC-FID.
Author Contributions:
Conceptualization, S.R.-B., E.G.-M., N.R.-C., M.E.L.-G. and R.M.; methodol-
ogy, S.R.-B., E.G.-M., N.R.-C., M.E.L.-G., B.G.-S. and R.M.; software, S.R.-B., E.G.-M., N.R.-C. and
M.E.L.-G.; validation, S.R.-B., E.G.-M., N.R.-C., M.E.L.-G. and R.M.; formal analysis, S.R-B. and
E.G.-M.; investigation, S.R.-B.; resources, E.G.-M., N.R.-C., M.E.L.-G. and R.M.; data curation, S.R.-B.,
E.G.-M., N.R.-C. and M.E.L.-G.; writing—original draft preparation, S.R.-B., E.G.-M., N.R.-C. and
M.E.L.-G.; writing—review and editing, S.R.-B., E.G.-M., N.R.-C. and M.E.L.-G.; visualization, S.R.-B.,
E.G.-M., N.R.-C., M.E.L.-G., B.G.-S. and R.M.; supervision, S.R.-B., E.G.-M., N.R.-C., M.E.L.-G., B.G.-S.
and R.M.; project administration. E.G.-M., N.R.-C., M.E.L.-G. and R.M.; funding acquisition, R.M. All
authors have read and agreed to the published version of the manuscript.
Funding:
This research was funded by the Ministry of Science and Innovation, the state research
agency and the European Union NextGenerationEU/PRTR [project TED2021-129917B-I00].
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
The data presented in this study are available on request from the
corresponding author.
Acknowledgments:
The authors are grateful to the Analysis Service Unit facilities of ICTAN for
the chromatography analysis. This work was supported by the Complutense University through a
research staff contract in the “Investigo programme” (CT36/22-30-UCM-INV).
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds are available from the authors.
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