Nutritional Value and Volatile Compounds of Black Cherry (Prunus serotina) Seeds

Abstract

Prunus serotina (black cherry), commonly known in Mexico as capulín, is used in Mexican traditional medicine for the treatment of cardiovascular, respiratory, and gastrointestinal diseases. Particularly, P. serotina seeds, consumed in Mexico as snacks, are used for treating cough. In the present study, nutritional and volatile analyses of black cherry seeds were carried out to determine their nutraceutical potential. Proximate analysis indicated that P. serotina raw and toasted seeds contain mostly fat, followed by protein, fiber, carbohydrates, and ash. The potassium content in black cherry raw and toasted seeds is high, and their protein digestibility-corrected amino acid scores suggest that they might represent a complementary source of proteins. Solid phase microextraction and gas chromatography/flame ionization detection/mass spectrometry analysis allowed identification of 59 and 99 volatile compounds in the raw and toasted seeds, respectively. The major volatile compounds identified in raw and toasted seeds were 2,3-butanediol and benzaldehyde, which contribute to the flavor and odor of the toasted seeds. Moreover, it has been previously demonstrated that benzaldehyde possesses a significant vasodilator effect, therefore, the presence of this compound along with oleic, linoleic, and α-eleostearic fatty acids indicate that black cherry seeds consumption might have beneficial effects on the cardiovascular system.

Full text

Molecules 2015, 20, 3479-3495; doi:10.3390/molecules20023479
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Nutritional Value and Volatile Compounds of Black Cherry
(Prunus serotina) Seeds
Leticia García-Aguilar 1,2, Alejandra Rojas-Molina 2,*, César Ibarra-Alvarado 2,
Juana I. Rojas-Molina 2, Pedro A. Vázquez-Landaverde 3, Francisco J. Luna-Vázquez 2
and Miguel A. Zavala-Sánchez 4
1 Doctorado en Ciencias Biológicas y de la Salud, Universidad Autónoma Metropolitana,
Unidad Xochimilco, Mexico, D.F. 04960, Mexico; E-Mail: laetitia_spp@yahoo.com
2 Laboratorio de Investigación Química y Farmacológica de Productos Naturales,
Facultad de Química, Universidad Autónoma de Querétaro, Querétaro, Qro. 76010, Mexico;
E-Mails: cibarra@uaq.mx (C.I.-A.); jirojasmolina@gmail.com (J.I.R.-M.);
fjlunavz@yahoo.com.mx (F.J.L.-V.)
3 Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada del Instituto Politécnico
Nacional, Unidad Querétaro. Cerro Blanco No. 141. Col. Colinas del Cimatario, Querétaro,
Qro. 76090, Mexico; E-Mail: pavazquez@ipn.mx
4 Departamento de Sistemas Biológicos, Universidad Autónoma Metropolitana, Unidad Xochimilco,
México, D.F. A.P. 23-181, Mexico; E-Mail: mzavala@correo.xoc.uam.mx
* Author to whom correspondence should be addressed; E-Mail address: rojasa@uaq.mx;
Tel.: +52-442-192-1200 (ext. 5527).
Academic Editor: Luca Forti
Received: 4 January 2015 / Accepted: 11 February 2015 / Published: 17 February 2015
Abstract: Prunus serotina (black cherry), commonly known in Mexico as capulín, is used
in Mexican traditional medicine for the treatment of cardiovascular, respiratory, and
gastrointestinal diseases. Particularly, P. serotina seeds, consumed in Mexico as snacks, are
used for treating cough. In the present study, nutritional and volatile analyses of black cherry
seeds were carried out to determine their nutraceutical potential. Proximate analysis
indicated that P. serotina raw and toasted seeds contain mostly fat, followed by protein,
fiber, carbohydrates, and ash. The potassium content in black cherry raw and toasted seeds
is high, and their protein digestibility-corrected amino acid scores suggest that they might
represent a complementary source of proteins. Solid phase microextraction and gas
chromatography/flame ionization detection/mass spectrometry analysis allowed identification of
OPEN ACCESS

Molecules 2015, 20 3480
59 and 99 volatile compounds in the raw and toasted seeds, respectively. The major volatile
compounds identified in raw and toasted seeds were 2,3-butanediol and benzaldehyde, which
contribute to the flavor and odor of the toasted seeds. Moreover, it has been previously
demonstrated that benzaldehyde possesses a significant vasodilator effect, therefore, the
presence of this compound along with oleic, linoleic, and α-eleostearic fatty acids indicate
that black cherry seeds consumption might have beneficial effects on the cardiovascular system.
Keywords: Prunus serotina seeds; black cherry seeds; volatile compounds; proximal
analysis; amino acid profile
1. Introduction
Prunus serotina Ehrh (American black cherry), commonly called “capulín” in Mexico, is a native
North American tree that belongs to the family Rosaceae [1]. It grows wildly or under cultivated
conditions in Mexican highlands and in some regions of Guatemala, Colombia, and Venezuela [2].
In recent times, it has spread widely in some European countries, like Belgium, the Netherlands, and
Germany [3]. P. serotina is a very fast-growing tree which has an oval silhouette, its low branches
normally droop and touch the ground, the leaves are dark green and shiny; the fruit is a little juice drupe
about 1 cm long with a stone which contains a seed [4].
In Mexico, P. serotina has been used since colonial times for nourishment and medicinal purposes.
The fruit is commonly consumed fresh, as jam, liquors or syrups, and the seeds are consumed roasted
and salted as snacks [2]. In Mexican traditional medicine, teas and syrups prepared from the leaves and
fruits are highly appreciated for treating hypertension, stomach upsets, mouth infections, diarrhea,
malaria, bronchitis, and cough [5,6], and the seeds are used in decoction for the treatment of cough [5].
Black cherry bark has been used by the Iroquois, Ojibwa, Malecite, and Delaware indigenous people
from the North American boreal forest regions of Canada for treating diabetes-related symptoms [7].
Recently, our research group carried out chemical and pharmacological studies of the leaves, fruits
and seeds of P. serotine. A bio-directed phytochemical study of the methanolic extract of the leaves led
to the isolation of hyperoside and ursolic acid as the main vasodilator compounds. It was also found that
benzyl alcohol, benzaldehyde, cinnamyl alcohol, and cinnamaldehyde were the major constituents of the
essential oil obtained from the leaves, these compounds promoted vascular smooth muscle relaxation [8].
Regarding P. serotina fruits, we found that they have a high content of phenolic compounds such as
chlorogenic acid, gallic acid, caffeic acid, catechin, epicatechin, quercetin, and kaempferol glycosides,
which are directly related to the high antioxidant capacity and significant vasodilatory effect of the
aqueous extract of the fruits [9]. Additionally, physicochemical and chemical characterization of black
cherry seed oil demonstrated that it is mainly composed of polyunsaturated fatty acids, including oleic,
linoleic, and α-eleostearic acids [10]. These results support the potential therapeutic significance of
P. serotina seed oil, since it has been extensively demonstrated that consumption of unsaturated fatty
acids reduce plasma lipids and reduce atherogenesis by decreasing inflammation of macrophages and
vascular endothelial cells [11,12]. Moreover, it has been reported that α-eleostearic acid is effective in

Molecules 2015, 20 3481
suppressing growth in cancer cells, and it has been proposed as a chemotherapeutic agent against breast
cancer [13].
Although black cherry seeds contain cyanogenic glycosides [14], there are no reports of human
intoxication related to their intake, since they are consumed toasted, which indicates that the toasting
process decreases the content of these compounds [15]. Heat treatment also provokes emission of volatile
compounds contained in the seeds, which undoubtedly contribute to their pleasant and characteristic
flavor. These volatile components might also possess pharmacological activity [16].
Currently, the nutritional value of black cherry seeds and their volatile components have not been
investigated. Therefore, in the present study the proximate composition, vitamin and mineral content of
these seeds were determined in order to assess their nutritional value. In addition, the volatile compounds
present in the seeds were analyzed by gas chromatography coupled to mass spectrometry.
2. Results and Discussion
2.1. Proximate Composition
Proximate compositions of raw and toasted black cherry seeds, Prunus dulcis (almonds) and Arachis
hypogaea (peanuts) are shown in Table 1. There were no significant differences between protein, ash,
crude fiber or carbohydrate contents of the raw and roasted seeds, suggesting that the toasting process
does not affect the proximate composition. The mean values of protein content were 37.95% ± 0.16%
and 36.55% ± 0.22% for raw and toasted seeds, respectively. These values were significantly higher than
those of almonds (19.91%), and peanuts (22.82%), whose protein content is consistent with earlier
reports [17,18]. P. serotine seeds possess a protein content which is comparable to that of seeds of other
Prunus species, including apricots (P. armeniaca L., 37.4%), sweet cherries (P. avium L. 31.7%), sour
cherries (P. cerasus L., 31.7%), nectarines (P. persica ar. nectarina (Aiton) Maxim, 38.7%), peaches
(P. persica (L.) Batsch var. persica, 33.4%), and plums (P. domestica L., 35.9%) [19].
Table 1. Proximate composition of raw and toasted black cherry seeds, almond, and peanut.
Component
(% Dry Basis)
Raw Black
Cherry Seeds
Toasted Black
Cherry Seeds Almonds Peanuts
Moisture 8.92 ± 0.42 a 10.75 ± 0.35 a 6.08 ± 0.4 b 5.45 ± 0.38 c
Fat 40.37 ± 0.73 a 39.97 ± 0.20 a 49.64 ± 0.42 b 41.12 ± 1.51 a
Protein 37.95 ± 0.16 a 36.55 ± 0.22 a 19.91 ± 0.01 b 22.82 ± 0.01 c
Ash 3.19 ± 0.18 a 2.72 ± 0.21 a 3.18 ± 0.21 a 2.41 ± 0.19 a
Crude Fiber 10.73 ± 1.49 a 12.12 ± 4.06 a 10.91 ± 1.45 a 9.21 ± 1.59 a
Carbohydrates 7.76 ± 2.24 a 8.65 ± 4.28 a 10.26 ± 1.98 b 18.95 ± 2.68 c
Notes: Data are given as mean ± standard deviation (n = 3 independent experiments performed in different
samples). a, b and c: Values in the same row followed by the same superscript letter are not significantly
different (p > 0.05).
Lipid content of P. serotina raw (40.37% ± 0.73%) and toasted seeds (39.97% ± 0.20%) was not
significantly different from that of peanuts (41.12% ± 1.51%). However, it was significantly lower than
almonds lipid content (49.64% ± 0.42%). It is well known that seed oils are mainly composed by
mono- and polyunsaturated fatty acids, thus oleic (61%) and linoleic (29%) acids are the main fatty acids

Molecules 2015, 20 3482
contained in almond; oleic acid (81%) is abundant in peanut oil [20], whereas, black cherry seed oil is
rich in oleic (35%), linoleic (27%) and α-eleostearic (27%) acids [10].
These findings indicate that P. serotina edible seeds are a good source of unsatured fatty acids with
potential health benefits [21]. The mean values of ash and crude fiber of raw and toasted P. serotina
seeds, almonds and peanuts did not differ significantly. The crude fiber content was similar to that of
other seeds and nuts that represent a complementary source of fiber, like hazelnut (9%–13%) or pumpkin
seeds (12.1%) [22,23]. Adequate intake fiber is related to the obesity prevention and better glycemic
control in patients with type 2 diabetes mellitus [24,25].
2.2. Minerals
The mineral composition (Ca, Fe, Mg, P, K, Zn and Na) of raw and toasted black cherry seeds,
almonds and peanuts are presented in Table 2. The Mg content of raw and toasted black cherry seeds
was unaffected by heat processing, but the Ca, Fe, P, K, Zn, and Na content diminished after the toasting
process. Usually, nuts and seeds are consumed toasted and salted, and toasting might have an important
influence on their nutrimental quality. Chitra et al. [26] and Gamel et al. [27] have pointed out that Ca
and Fe content significantly reduced after toasting or autoclaving seeds of soybean and pigeon peas.
Table 2. Mineral composition of raw and toasted black cherry seeds, almond and peanut.
Mineral (Dry Basis)
mg/100 g
Raw Black
Cherry Seeds
Toasted Black
Cherry Seeds Almonds Peanuts
Ca 192.30 ± 0.58 a 127.11 ± 17.51 b 305.43 ± 1.88 c 91.43 ± 0.05 d
Fe 9.49 ± 0.3 a 1.21 ± 0.003 b 6.08 ± 0.01 c 8.31 ± 0.02 d
Mg 249.15 ± 0.34 a 216.68 ± 18.75 a 282.09 ± 0.32 b 172.75 ± 0.77 c
P 439.0 ± 0.16 a 323.40 ± 0.14 b 387.03 ± 0.7 c 347.41 ± 0.07 d
K 873.22 ± 12.64 a 454.82 ± 0.41 b 656.25 ± 23.80 c 571.57 ± 10.03 d
Zn 3.40 ± 0.10 a 2.96 ± 0.24 b 4.48 ± 0.17 c 3.92 ± 0.10 d
Na 82.98 ± 0.90 a 23.59 ± 0.8 b 76.57 ± 0.38 a 62.99 ± 0.65 c
Notes: Data are given as mean ± standard deviation (n = 3 independent experiments performed in different
samples). a, b, c and d: Values in the same row followed by the same superscript letter are not significantly
different (p > 0.05).
Raw black cherry seeds possess a higher content of Ca, Fe, Mg, K and Na than that found in peanuts.
On the other hand, Fe, K, and Na content is greater than that of almonds. Interestingly, the K content in
black cherry seeds (873.22 ± 12.64 mg/100 g) is significantly higher than that of almonds and peanuts,
suggesting that P. serotina seeds represent a good complementary source of this mineral.
2.3. Vitamins
Vitamin analysis showed that raw and toasted P. serotina seeds do not contain vitamins A and C.
Vitamin E or α-tocopherol was detected at a concentration of 3.916 mg/100 g in raw seeds, while in
toasted seed it was absent. This lost may be associated with vitamin degradation due to temperature
exposure [27]. Our results are in agreement with previous studies carried out on other seeds and nuts,
such as pumpkin seeds, walnuts and peanuts, which do not contain detectable values of vitamins A and

Molecules 2015, 20 3483
C [28,29]. Vitamin E content of black cherry seeds is similar to that of pine nuts (4.1 mg/100 g) and
peanuts (6.1 mg/100 g), however it is lower than that of almonds and hazelnuts (24.2 mg/ 100 g and
31.4 mg/ 100 g, respectively) [28].
2.4. Protein Nutritional Quality
Since black cherry seeds contain higher levels of protein (37.95% ± 0.16%) than other seeds, their
protein nutritional quality was assessed. Amino acid composition data are presented in Table 3. It is
important to mention that in this experiment tryptophan was not determined.
Table 3. Protein amino acids composition of raw and toasted black cherry seeds.
Amino
Acid
Raw Seeds mg/g
Protein
Toasted Seeds mg/g
Protein
Asp
112.29
116.97
Glu
256.84
273.73
Ser
32.84
42.11
His
21.60
21.29
Gly
37.43
38.82
Thr
52.85
59.16
Arg
84.24
87.42
Ala
41.47
44.06
Tyr
48.75
60.99
Met
8.93
9.83
Val
45.48
45.62
Phe
48.64
52.00
Ile
39.17
40.33
Leu
75.10
82.11
Lys
8.85
11.17
Another protein quality measure is digestibility. Differences among the in vitro protein digestibility
values of raw and toasted black cherry seeds were not significant (88.12% ± 0.72% and
89.40% ± 1.32%, respectively). These values were similar to that of almonds (90.15% ± 0.85%),
however they were lower than those of peanuts (94.06% ± 0.78%) and casein (98.51% ± 0.82%), which
was used as control. It has been reported that in vitro protein digestibility values greater than 80% are
related to an efficient amino acid bioavailability [27]. Therefore, these results suggest that black cherry
seed proteins are highly bioavailable.
Considering these findings, the protein digestibility-corrected amino acid score (PDCAAS) was
determined. This method is accepted as the most recognized approach for assessing the protein quality
of foods [30]. Every essential amino acid receives a score, but the final PDCAAS value corresponds to
that of the limiting amino acid. The highest PDCAAS value for a given protein is 1.0, which indicates
that a protein provides adequate amounts of all the essential amino acids [31]. Table 4 shows that lysine
is the limiting amino acid in P. serotina seeds, therefore, PDCAAS values for raw and toasted black
cherry seeds protein are 0.13 and 0.18, respectively. These values are lower than those reported for

Molecules 2015, 20 3484
almonds (0.23) [17] and peanuts (0.69) [32]. These results suggest that black cherry seeds could be a
complementary source of proteins.
Table 4. Black cherry seeds amino acid score (AAS).
AA FAO Reference
Pattern
AAS * AAS *
Raw Seeds Toasted Seeds
His 19 1.37 1.12
Thr 34 1.55 1.74
Met 25 0.36 0.39
Val 35 1.30 1.33
Phe 63 0.77 0.82
Ile 28 1.40 1.44
Leu 66 1.38 1.24
Lys ** 58 0.15 0.19
Notes: * Amino acid score (AAS) = AA content of test protein/reference AA pattern, where
reference AA pattern is the amino acid requirement for a preschool child (2–5 years) [30].
** Limiting amino acid.
2.5. Volatile Compounds
Volatile compounds of raw and toasted black cherry seeds were extracted by head space solid phase
micro extraction and analyzed by gas chromatography-mass spectrometry, using DB-5 and Wax
capillary columns in order to detect a wide range of polar and non-polar compounds. A total of 59 and
99 volatile compounds were identified in the raw and toasted P. serotina seeds, respectively (Table 5).
The identified volatile compounds comprise aldehydes, alcohols, ketones, carboxylic acids, esters,
hydrocarbons, and pyrazines.
The predominant aldehyde identified in raw and toasted seeds was benzaldehyde. This compound has
a characteristic pleasant almond-taste and aroma [33] and has been identified in bitter and sweet
almonds [34], hazelnuts [33], and seeds of other species of the genus Prunus [35,36]. Benzaldehyde is
produced by enzymatic degradation of the cyanogenic glycosides amygdalin and prunasin [35,37,38].
Considering on one hand that benzaldehyde content in toasted seeds was higher than that in raw seeds,
and on the other, that bitterness attributed to the presence of amygdalin [39,40] diminished in toasted seeds,
it is very likely that the toasting process may induce benzaldehyde formation from cyanogenic glycosides.
Benzaldehyde might also be generated from phenylalanine during heating processes [41,42] as was
demonstrated by Alasalvar et al. [33] in hazelnuts, pumpkin seeds [43], and peanuts [44].
It is worth noting that we have previously identified benzaldehyde as one of the major components in
black cherry leaves essential oil, we also proved that this compound induces a significant
concentration-dependent vasodilator effect [8]. Therefore, the presence of this compound along with
oleic, linoleic, and α-eleostearic fatty acids indicate that black cherry seeds consumption might have
beneficial effects on the cardiovascular system.

Molecules 2015, 20 3485
Table 5. Volatile compounds on raw and toasted black cherry seeds.
RI
Calculated a
RI
Literature b Compound Raw c Toasted c
ID e
DB5 WAX DB5 WAX (ppm
d) (ppm
d)
Aldehydes
573 805 801 Propanal, 2-methyl- 0.604 MS, RI
638 640 2-Butenal 0.180 MS, RI
642 908 642 Butanal, 3-methyl- 1.095 MS, RI
652 910 653 Butanal, 2-methyl- 1.419 MS, RI
695 965 695 970 Pentanal 2.065 MS, RI
740 740 2-Butenal, 2-methyl- 0.500 MS, RI
1074 1078 Hexanal 0.096 MS, RI
834 1440 835 1443 Furfural 2.609 MS, RI
902 905 Heptanal 0.084 MS, RI
908 909 Propanal, 3-(methylthio)- 0.041 MS, RI
1199 1196 2-Hexenal, (E)- 0.014 MS, RI
964 963 2-Furancarboxaldehyde, 5-methyl- 0.112 MS, RI
967 1508 969 1508 Benzaldehyde 1.371 7.597 MS, RI
1053 1053 Benzeneacetaldehyde 0.411 MS, RI
1106 1108 Nonanal 0.056 0.201 MS, RI
1443 1455 3-Furaldehyde 0.090 MS, RI
1221 1697 1221 1697 2,4-Nonadienal, (E,E)- 0.091 MS, RI
1279 1930 1279 1933 Benzeneacetaldehyde, alpha.-ethylidene- 0.045 MS, RI
Ketones
707 1303 708 1301 2-Butanone, 3-hydroxy- 0.329 0.361 MS, RI
986 986 3-Octanone 0.055 MS, RI
1027 1043 1,2-Cyclopentanedione, 3-methyl- 0.221 MS
1067 1958 1067 1957 Ethanone, 1-(1H-pyrrol-2-yl)- 0.233 MS,RI
1071 1071.6 Acetophenone 0.051 MS,RI
1114 1117 1,7-Octadien-3-one, 2-methyl-6-methylene- 0.037 MS,RI
1448 Cyclohexanone, 5-methyl-2-(1-methylethyl)-,
(2S-trans)- 0.037 MS
1486 1489 Ethanone, 1-(2-furanyl)- 0.119 MS, RI
1487 1-(3H-Imidazol-4-yl)-ethanone 0.226 MS
1151 1151 4H-Pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-
methyl- 0.107 MS, RI
1569 1573 2-Cyclopentene-1,4-dione 1.536 MS, RI
1588 1587 Ethanone, 1-(2-pyridinyl)- 0.526 MS, RI
1814 1,2-Cyclopentanedione, 3-methyl- 0.134 MS
2012 2(3H)-Furanone, dihydro-3-hydroxy-4,4-
dimethyl- 0.101 MS

Molecules 2015, 20 3486
Table 5. Cont.
RI
Calculated a
RI
Literature b Compound Raw c Toasted c ID e
DB5 WAX DB5 WAX (ppm
d) (ppm
d)
Carboxylic acids
613 1415 610 1415 Acetic acid 2.163 5.939 MS, RI
1608 Benzoic acid, hydrazide 0.040 MS
1616 Butanoic acid, 4-hydroxy- 0.184 0.656 MS
1829 1827 Hexanoic acid 0.282 0.089 MS, RI
2028 2030 Octanoic Acid 0.110 0.209 MS, RI
Esters
719 972 720 971 Butanoic acid, methyl ester 0.019 MS, RI
774 1007 776 1007 Acetic acid, 2-methylpropyl ester 0.191 0.096 MS, RI
826 1076 825 1075 Pentanoic acid, methyl ester 0.166 MS, RI
878 1115 877 1115 1-Butanol, 3-methyl-, acetate 0.282 0.404 MS, RI
880 880 1-Butanol, 2-methyl-, acetate 0.260 MS, RI
912 1616 912 1617 Butyrolactone 0.297 MS, RI
925 926 Hexanoic acid, methyl ester 0.120 MS, RI
1320 1317 Heptanoic acid, ethyl ester 0.061 MS, RI
1045 Pantolactone 0.192 MS
1099 1607 1100 1605 Benzoic acid, methyl ester 0.162 MS,RI
1167 1165 Acetic acid, phenylmethyl ester 0.096 MS,RI
Alcohols
615 1085 618 1086 1-Propanol, 2-methyl- 0.389 0.229 MS, RI
918 920 Isopropyl Alcohol 0.080 MS, RI
734 1189 730 1190 1-Butanol, 3-methyl- 0.173 MS, RI
738 1189 1-Butanol, 2-methyl-, (+/−)- 0.381 MS
767 1231 766 1232 1-Pentanol 0.595 0.536 MS, RI
797 1584 800 1583 2,3-Butanediol [R-(R*,R*)]- 17.039 17.448 MS, RI
1088 1,2-Cyclopentanediol, trans- 0.030 MS
1136 1136 1-Butanol 0.050 0.062 MS, RI
858 1635 858 1638 2-Furanmethanol 0.747 MS, RI
955 1700 953 2-Furanmethanol, 5-methyl- 0.096 MS, RI
1334 1335 1-Hexanol 0.201 MS, RI
1039 1866 1039 1866 Benzyl alcohol 0.332 1.019 MS, RI
1051 3-Octen-1-ol 0.069 MS
1379 1379 Ethanol, 2-butoxy- 0.063 MS, RI
1580 Cyclohexanol, 5-methyl-2-(1-methylethyl)-,
(1α, 2β, 5α)- 0.743 MS
1885 3,6,9,12-Tetraoxatetradecan-1-ol 0.008 MS
1903 1905 Phenylethyl Alcohol 0.065 0.166 MS, RI
1684 2,6-Bis(1,1-dimethylethyl)-4-
(1-oxopropyl)phenol 0.010 0.014 MS

Molecules 2015, 20 3487
Table 5. Cont.
RI
Calculated a
RI
Literature b Compound Raw c Toasted c ID e
DB5 WAX DB5 WAX (ppm
d) (ppm
d)
Hydrocarbons
647 923 648 924 Benzene 0.043 0.086 MS, RI
765 1029 765 1029 Toluene 0.052 0.110 MS, RI
1094 Undecane 0.030 MS
1126 1123 Benzene, 1,3-dimethyl- 0.050 MS, RI
862 863 Ethylbenzene 0.022 MS, RI
872 Cyclopropane, propyl- 0.324 MS
1166 1164 p-Xylene 0.010 MS, RI
893 1237 894 1236 Styrene 0.108 0.084 MS, RI
899 Nonane 0.020 0.074 MS
931 2,4-Octadiene 0.057 MS
1238 1264 1,3,5,7-Cyclooctatetraene 0.300 MS
996 996 Benzene, 1,3,5-trimethyl- 0.040 MS, RI
999 997 Decane 0.096 0.089 MS
1033 1079 1030 D-Limonene 0.025 0.048 MS, RI
1412 Benzene, 2-ethyl-1,4-dimethyl- 0.011 MS
1413 Benzene, 1-ethyl-2,3-dimethyl- 0.027 MS
1125 1120 Benzene, 1,2,3,4-tetramethyl- 0.040 MS, RI
1303 1300 Tridecane 0.015 0.027 MS, RI
1399 1400 Tetradecane 0.015 0.040 MS, RI
2056 1,4,7,10,13,16-Hexaoxacyclooctadecane 0.029 MS
Pyrazines
826 1247 827 1247 Pyrazine, methyl- 3.745 MS, RI
896 1487 1491 2,3,5-Trimethyl-6-ethylpyrazine 0.221 MS, RI
915 1306 915 1308 Pyrazine, 2,5-dimethyl- 7.344 MS, RI
1312 1314 Pyrazine, 2,6-dimethyl- 1.297 MS, RI
998 1365 998 1367 Pyrazine, 2-ethyl-6-methyl- 0.701 MS, RI
1002 1384 1005 1381 Pyrazine, trimethyl- 1.685 MS, RI
1330 1326 Pyrazine, 2,3-dimethyl- 0.287 MS, RI
1371 1367 Pyrazine, 2-ethyl-5-methyl- 1.494 MS, RI
1078 1425 1078 1430 Pyrazine, 3-ethyl-2,5-dimethyl- 1.907 MS, RI
1085 1085 Pyrazine, 2-ethyl-3,5-dimethyl- 0.143 MS, RI
1086 1458 1088 1457 Pyrazine, tetramethyl- 0.106 0.597 MS, RI
1411 1415 Pyrazine, 2,6-diethyl- 0.066 MS, RI
1094 1091 Pyrazine, 2,5-diethyl- 0.106 MS, RI
1472 1485 Pyrazine, 2-ethenyl-6-methyl- 0.105 MS, RI
1147 1609 1605 5H-5-Methyl-6,7-dihydrocyclopentapyrazine 0.500 MS, RI
1153 1475 1156 1478 Pyrazine, 2,3-diethyl-5-methyl- 0.130 MS, RI
1157 1156 Pyrazine, 3,5-diethyl-2-methyl- 0.245 MS, RI
1161 1357 2,5-Dimethyl-3-n-pentylpyrazine 0.021 MS
1683 1679 1-(6-Methyl-2-pyrazinyl)-1-ethanone 0.146 MS, RI
1318 1254 Pyrazine, 2-butyl-3,5-dimethyl- 0.019 MS
1705 1740 Pyrazinamide 0.208 MS

Molecules 2015, 20 3488
Table 5. Cont.
RI
Calculated a
RI
Literature b Compound Raw c Toasted c ID e
DB5 WAX DB5 WAX (ppm
d) (ppm
d)
Pyrroles and Furans
811 1165 811 1168 1H-Pyrrole, 1-ethyl- 0.144 MS, RI
847 841 1H-Pyrrole, 3-methyl- 0.082 MS, RI
948 1H-Pyrrole, 1-butyl- 0.021 MS
891 1122 892.1 1123 2-n-Butylfuran 0.707 MS, RI
991 1211 991 1213 Furan, 2-pentyl- 0.077 0.236 MS, RI
1037 2,3-Dihydrofuran 0.008 MS
1016 2004 1016 2006 1H-Pyrrole-2-carboxaldehyde 0.114 MS, RI
1076 2020 1076 2020 2-Pyrrolidinone 0.477 MS, RI
1675 1678 2-Pyrrolidinone, 1-methyl- 0.057 MS, RI
Miscellaneous
632 643 Methanethiol 0.046 MS
559 701 Dimethyl sulfide 0.052 0.071 MS
567 531 Methylene chloride 0.844 0.474 MS
612 1009 615 1010 Trichloromethane 0.059 0.028 MS, RI
724 Propanamide, N,N-dimethyl- 0.025 MS
850 850 Oxazole, trimethyl- 0.034 MS, RI
1020 1020 Benzene, 1,4-dichloro- 0.450 0.253 MS, RI
1419 Benzene, 1,2-dichloro- 0.450 MS
1710 6-Aminoindoline 0.136 MS
1923 1912 Benzonitrile, 2-methyl- 0.060 MS
1537 N-(2-Benzoyl-4-nitrophenyl)-4-tert-
butylbenzamide 0.041 MS
2051 Octaethylene glycol 0.007 MS
Notes: a Calculated Kovats retention index on DB-5 or Wax column using a n-alkanes series; b Reported Kovats
retention index on library NIST; c Average of 3 replicates. Coefficient of variation < 9.2%; d Semi-quantitative
values. e MS = tentative identification by comparison to mass spectra in NIST library, RI = identification by
comparison of calculated Kovats retention index to that reported in literature.
The most abundant alcohol identified in P. serotina seeds was 2,3-butanediol, which was also the
major volatile compound in raw (17.03 ppm) and toasted seeds (17.44 ppm). This alcohol is the major
volatile component of sweet kernels and has been associated to their characteristic taste [34].
2,3-butanediol is also found in cheeses [45] and honey [46]. Recently, it has been reported that this
metabolite is abundant in roasted Trichosanthes kirilowii seeds, however it was absent in the raw seeds,
which suggests that 2,3-butanediol was generated during the toasting process [47]. In contrast, our results
indicated that 2,3-butanediol levels in black cherry seeds were not significantly different before and after
toasting. Benzyl alcohol, predominantly found in toasted seeds, imparts a sharp, burning taste and a faint
aroma in toasted almonds [48]. This compound was previously detected as one of the major volatiles of
black cherry leaves and also displays a vasodilator effect [8]. Regarding 1-pentanol, detected in both raw
and toasted seeds, it has been proposed that it derives from the oxidation of linoleic acid, and its
concentration increases with storage time in almonds [49].

Molecules 2015, 20 3489
Acetic acid was the main volatile carboxylic acid found in raw and toasted P serotina seeds. This
carboxylic acid can be regarded as a result of long-chain fatty acids degradation and it is often related to
a strong sour odor [50]. Esters were detected in lesser quantities, some of them, such as methyl esters of
short chain fatty acids, were found in raw seeds, but not in toasted seeds. Hydrocarbons and ketones
were minor compounds in both raw and toasted seeds.
Pyrazines and pyrroles were other major volatiles identified exclusively in toasted black cherry seeds.
These compounds are produced during the toasting process from free amino acids and monosaccharides
by the Maillard reaction through Strecker degradation [33], particularly, ethyl-methyl-, ethyldimethyl-,
and diethylmethylpyrazines, are formed in the reaction of glucose and fructose with alanine and glycine [51].
The most abundant pyrazine in black cherry toasted seeds was 2,5-dimethylpyrazine, followed by
methylpyrazine, 3-ethyl-2,5-dimethylpyrazine and trimethylpyrazine. The first one has been previously
reported as a major pyrazine in roasted hazelnuts [33] and toasted almonds [48]. Pyrazines contribute to
the characteristic toasted aroma in chesnuts [52], and peanuts [53], almonds [54], and pyrroles
significantly are responsible for the characteristic toasted aroma of different thermal treated foods [44].
3. Experimental Section
Reagents and standards were purchased from Sigma-Aldrich (St. Louis, MO, USA), unless
otherwise noted. Solvents were purchased from Baker-Mallincrodt (JT Baker, Mallinckrodt Baker Inc.,
Phillipsburg, NJ, USA).
3.1. Samples
Ripe black cherry fruits were cultivated in Huejotzingo, Puebla (México) and harvested in May of
2011. Subsequently, the seeds were removed from the pulp with plastic knives, washed and allowed to
dry at 25 °C during 48 h. Finally, the seeds were stored at −70 °C until analysis.
All the analyses were carried out on raw and toasted seeds. Toasting was performed in a comal
(traditional Mexican iron griddle) during 20 min at 125 °C. Then, the seeds were rotated frequently to
avoid overheating and to obtain homogenous toasting. Raw and toasted seeds were cracked and opened
with pliers to get the kernel.
Taking into account that black cherry toasted seeds are consumed by Mexican people as snacks,
almonds (Prunus dulcis) and peanuts (Arachis hypogaea) samples were analyzed for comparative
purposes. Both seeds were purchased in a local market in the city of Queretaro, Queretaro (México).
3.2. Chemical Proximate Analysis
Chemical proximate analysis was carried out on raw and toasted black cherry seeds, almonds and
peanuts by using AOAC methods (AOAC, 2000). Moisture, protein, fat, ash, crude fiber and
carbohydrates contents were determined by methods 950.46, 928.08, 960.39, 920.153 and 985.29,
respectively. Total carbohydrate content (on dry weight basis) was calculated by difference
[100 − (protein + lipids + ash + crude fiber)].

Molecules 2015, 20 3490
3.3. Determination of Vitamins A, C, and E
Vitamins and carotenes were determined by using AOAC methods (2000) for vitamin A (960.46),
vitamin C (967.22), and vitamin E (992.03).
3.4. Mineral Content
Sodium, potassium, calcium, magnesium and iron content of samples was determined by method
985.35 described in Association of Official Analytical Chemists (AOAC, 2000). Phosphorous was
determined according to method 965.17 (AOAC, 2000).
3.5. In Vitro Protein Digestibility
The in vitro protein digestibility of dry samples was estimated by using the methodology of
Hsu et al. [55] and applying the equation Y = 234.84 − 22.56X, where Y is the in vitro protein digestibility
(%) and X is the pH of the protein sample suspension, after proteolysis with a multienzyme system
consisting of porcine pancreatic trypsin type IX, bovine pancreatic chymotrypsin type II, and porcine
intestinal peptidase grade III. The average value of three replicates is reported.
3.6. Amino Acid Analysis
Proteins were hydrolyzed in hydrochloric acid (JT Baker) and amino acids were analyzed using a
HPLC autoanalyzer (Waters 2487, Millipore, MA, USA), according to Bidlingmeyer et al. [56].
3.7. Nutritional Quality of Proteins
For predicting dietary protein quality, the in vitro protein digestibility and amino acid composition
were used to calculate PDCAAS (protein digestibility corrected amino acid score) according to the
FAO/WHO [30] prescribed formula:
PDCAAS = Amino acid score (of the most limiting AA) × Digestibility (1)
3.8. Volatile Compounds Analysis
Extraction conditions were based on previously published work of Krist et al. [52] and Agila et al. [54]
with some modifications. Fresh seeds (15 g) were blended in an electric blender (model O-20,
OsterizerTM, Boca Raton, FL, USA) for 15 s. The ground seeds (1 g) were transferred into a 20 mL vial,
along with 7 µg of a menthol solution (0.01% w/w) as an internal standard and sealed with a
Nickel-aluminum crimp cap provided with a needle-pierceable polytetrafluroethylene/silicone septum.
Vials were pre-equilibrated for 60 min at 50 °C. Solid-phase microextraction (SPME) was performed
with a 75 mm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber (Supelco Co,
Bellefonte, PA, USA). Extractions and injections were performed using a MPS2 autosampler (Gerstel,
Linthicum-Baltimore City, MD, USA) fitted with a vial heater. The fiber was exposed for
10 min in the head space of the vial for analytes adsorption. Subsequently, the fiber was removed from
the vial and placed into the chromatograph injection port for desorption.

Molecules 2015, 20 3491
Gas chromatography separation and quantification was carried out using an Agilent GC 7890A series
intrumenbt (Agilent Technologies, Inc., Santa Clara, CA, USA) equipped with a flame ionization
detector (GC-FID). Injection port and detector temperature was 230 °C. The injector was operated in the
splitless mode. The capillary columns used were an HP-5 60 m × 0.32 mm i.d., 0.32 µm film thickness;
Agilent Technologies, Inc.) and a DB-Wax (60 m × 0.32 mm i.d., 0.32 µm film thickness; Agilent
Technologies, Inc.). Oven temperature was programmed at initial temperature of 40 °C for 5 min, then
raised at 5 °C/min to 230 °C and hold for 15 min. Helium was used as the carrier gas at a constant flow
rate of 1 mL/min. A semi-quantitative evaluation was achieved by comparing individual peak area from
GC-FID response to that of the internal standard. Each tabulated value corresponds to the average
of 3 extraction replicates.
Gas Chromatography Mass Spectrometry (GC/MS) analysis was carried out using an Agilent GC
7890A series equipped with an Agilent 5975C Mass Spectrometer in electron impact mode (EI) and a
quadrupole analyzer. The temperatures of ion source and quadrupole were 230 and 250 °C respectively.
Transfer line was set at 280 °C. Full scan mode was used in a range of 33–300 uma, at a scan rate of
5.2/s, with an ionization voltage of 70 eV. The same chromatographic conditions as for GC-FID
were used. MSD ChemStation E.01.00.237 software (Agilent Technologies, Inc.) was employed for
data analysis.
Identification of volatile compounds was performed by comparing their mass spectra with those in
the NIST Mass Spectral Library (National Institute of Standards and Technology, Gaithersburg, MD,
USA). Retention indices of all the volatile compounds were determined by the modified Kovats method
reported by Van den Dool and Kratz [57]. MS identification was confirmed by comparing Kovats
retention indices (RI) to RI reported in the literature [58].
3.9. Statistical Analysis
Results of the experiments are expressed as the mean ± standard deviation (SD) from n = 3
experiments. The data were analyzed by a one-way ANOVA and the Tukey test. Differences between
the means were considered to be significant when p ˂ 0.05. Statistical treatment of data was performed
with the program Prism 4.0 (GraphPad Software, San Diego, CA, USA).
4. Conclusions
This study demonstrates that black cherry seeds have a significant content of minerals, particularly
potassium, lipids and proteins. Their PDCAAS values suggest that they might be considered as a
complementary source of protein. Additionally, the gas chromatography/mass spectrometry analysis
allowed identification of 59 and 99 volatile compounds in the raw and toasted seeds, respectively.
The major volatile components identified in raw and toasted P. serotina seeds were 2,3-butanediol
and benzaldehyde. The results derived from this study indicate that these seeds have nutraceutical
properties attributed to their high protein and potassium content and the presence of bioactive
compounds such as benzaldehyde.

Molecules 2015, 20 3492
Acknowledgments
Leticia García-Aguilar acknowledges Consejo Nacional de Ciencia y Tecnología (CONACYT) for
her Ph. D. scholarship. This work was supported by grants (a) FOFI-UAQ-2012 (Project FCQ-2012-25)
and (b) INFR-2014-01-226186 from CONACYT assigned to Alejandra Rojas Molina.
Author Contributions
Leticia García-Aguilar extracted and analyzed the volatile compounds and assessed nutritional
protein quality as part of her doctoral degree thesis. Alejandra Rojas-Molina designed this project,
coordinated all the activities, and supervised the chemical studies. César Ibarra-Alvarado helped in the
design of experiments. Pedro A. Vázquez-Landaverde conducted the final identification of volatile
compounds. Juana I. Rojas-Molina supervised the nutrimental analysis. Francisco J. Luna-Vázquez was
in charge of the fruit collection and identification and revised the manuscript. Miguel A. Zavala-Sánchez
contributed with the preparation of manuscript.
Conflicts of Interest
The authors declare no conflict of interest.
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© 2015 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 license
(http://creativecommons.org/licenses/by/4.0/).