Apricot kernel: Physical and chemical properties

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Sir:
The apricot, Prunus armeniaca L., is a member of the
Rosaceae, subfamily Prunoideae. Very few apricot cultivars
are grown commercially throughout the world. Instead, culti-
vars tend to be grown in only one region of a country, and
most would be virtually unknown outside of that region.
Turkey is the largest producer of apricots (538,000 metric
tons/yr) in the world. The hard, outer part of the pits, taken
separately, represents about 35,000 metric tons/yr, and the
kernels within the pits, taken separately, constitute 7,000 met-
ric tons/yr (1). The kernels are mainly used in production of
cosmetics, medicines, and scents, and pits are used as fuel.
The percentage of the kernel in the pit of apricot varies
from 18.8 to 38.0%, calculated as [(pits)/(pits + kernels)]
×
100 (2–11). The average dimensions of apricot kernels are:
length, 14.0–19.17 mm; width, 9.99–10.20 mm; thickness,
3.3–6.27 mm; geometric mean diameter, 9.89–10.31 mm; and
mass, 0.47–0.48 g (7,12,13). The 100-kernel weight range is
28.7–65.1 g (6,7,9,10). Physical properties of apricot kernels
are relevant in the design of equipment to be used in mechan-
ical processing (14).
Table 1 summarizes the chemical constituents of apricot
kernels. The reported protein content of apricot kernel ranged
from 14.1 to 45.3% (2,4,6,7,14–18). A PAGE study found
that apricot kernel proteins contain 84.7% albumin, 7.65%
globulin, 1.17% prolamin, and 3.54% glutelin. Nonprotein ni-
trogen is 1.17%, and other proteins are 1.85% (7). Research
on the physicochemical properties of proteins revealed a UV
absorption (
λ
max
) of 282 nm; a fluorescence spectrum (emis-
sion max) of 315 nm; and four subunits with molecular sizes
of 58,600, 37,400, 25,200, and 16,500 based on SDS-PAGE
(19).
Essential amino acids in apricot kernel constituted
32–34% (15) of the total amino acids. The major essential
amino acids (mmol/100 g meal) were arginine (21.7–30.5)
and leucine (16.2–21.6), and the predominant nonessential
amino acid was glutamic acid (49.9–68.0) (4). Table 2 pre-
sents data on
in vitro protein digestibility values for apricot
kernel flour and protein isolate.
Carbohydrate content of apricot kernel was reported vari-
ously as 25.5% (w/w) (20), 17.3% (6), and 18.1–27.9% (4).
The total sugar content was reported as 4.10% in undefatted
kernel and 7.76% in defatted kernel (7). Invert sugar content
was 5.86% (10). The sugar content of kernels from different
cultivars in Turkey is presented in Table 3 (14).
The oil content of the kernels (Table 1) varies from 27.7 to
66.7% (2,4,6–8,14,15,17,18). Table 4 indicates that the con-
tents of the major FA are oleic (58.3–73.4%) and linoleic
(18.8–31.7%) (6–8,14,17,22–26). The contents of unsaturated
FA (91.5–91.8%) and saturated FA (7.2–8.3%) (10,14) have
been reported, as well as neutral lipids (95.7–95.2%), glyco-
lipids (1.3–1.8%), and phospholipids (2.0%) (10). The kernel
oil contains 11.8 mg/100 g campesterol, 9.8 mg/100 g stig-
masterol, and 177.0 mg/100 g sitosterol (27).
The values for specific gravity, refractive index, iodine,
saponification number, and unsaponifiable matter for apricot ker-
nel oil are presented in Table 5. The ranges are 0.1–1.6 for un-
saponifiable matter (4,10,28,29), 187.3–199.0 for saponification
number (12,21,28), 90.0–104.8 for iodine value (8,10,21,28,29),
0.876–0.932 for specific gravity (8,12,21,28), and 1.464–1.480
(8,10,21) for the refractive index.
Copyright © 2006 by AOCS Press 469 JAOCS, Vol. 83, no. 5 (2006)
Paper no. J11111 in JAOCS 82, 469–471 (May 2006).
LETTERS TO THE EDITOR
Apricot Kernel: Physical and Chemical Properties
T
ABLE
1
Chemical Compositions of Apricot Kernels
a
Oil Protein Ash Arginine Leucine Glutamic acid
(%) (%) (%) (mmol/100 g) (mmol/100 g) (mmol/100 g) Reference
43.0–53.0
20.2
2.3
15
23.7–25.5
1.7–2.5
16
41.9–49.3 31.7–38.7 21.7–30.5 16.2–21.6 49.9–68.0 4
31.6–50.4 14.1–18.2 2.2–2.5 14
27.7–66.7 20.3–45.3 2
52.0 20.6 2.9 6
50.9–53.2
23.1–24.1 2.2–2.5 7
56.0 22.2 2.2 18
44.2–44.6 21.5 2.8 17
46.3–51.4
23.6–27.7
2.1–2.7
8
a
These data represent a number of cultivars.

Table 6 shows the kernels contain thiamine, riboflavin,
niacin, vitamin C (14), α-tocopherol, and δ-tocopherol (27).
The ranges for mineral content of apricot kernel (mg/100 g
dry matter) were: Na, 35.2–36.8; K, 473–570; Ca, 1.8–2.4,
Mg, 1
13–290; Fe, 2.14–2.82; Zn, 2.33–3.15 (8,14,30); and
single reports have appeared for Mn, 0.48; Ni, 0.14; and Co,
0.002 (30).
The use of apricot kernels for human nutrition is limited
because of their content of the toxic, cyanogenic glycoside
amygdalin, accompanied by minor amounts of prunasin.
Amygdalin, which is used in the treatment of human cancer
470 LETTER TO THE EDITOR
JAOCS, Vol. 83, no. 5 (2006)
TABLE 2
In vitro Protein Digestibility Values
a
for Apricot Kernel Flour,
Apricot Kernel Protein Isolate, and Casein (7)
Digestible protein
b
(%)
Enzyme system Casein Kernel flour Kernel protein isolate
Pepsin 33.4 ± 3.1 30.6 ± 2.5 32.8 ± 2.7
Trypsin 72.8 ± 2.5 30.7 ± 3.0 66.9 ± 2.9
Pancreatin 95.9 ± 1.8 35.5 ± 2.6 95.9 ± 2.4
Pepsin-pancreatin 99.1 ± 0.3 96.4 ± 1.2 98.1 ± 1.5
a
These data reprresent a number of cultivars.
b
Data are mean ± SD.
TABLE 3
Sugar Content (%) of Apricot Kernel (14)
Variety Glucose Fructose Sucrose
Hasanbey 1.03 0.45 3.01
Aprikoz 0.60 0.43 2.18
Hangarish Best 0.92 0.16 1.56
Tokaloˇglu 1.01 0.19 1.57
Hacıhalilogˇlu 0.76 0.12 1.47
Çatalogˇlu 0.28 0.33 0.85
Kabaas¸ı 0.57 0.25 1.47
Çölogˇlu 0.68 1.70 0.26
·
Ismailagˇa 0.86 1.20 0.70
Sogˇancı 0.71 1.67 0.43
S¸ekerpare 1.00 2.40 0.54
Mean ± SD 0.77 ± 0.23 0.81 ± 0.79 1.28 ± 0.83
TABLE 4
FA (%) Profile of Apricot Kernels
a
Palmitic Palmitoleic Stearic Oleic Linoleic Linolenic
(16:0) (16:1) (18:0) (18:1) (18:2) (18:3) Reference
4.4 0.1 0.2 69.0 26.0 0.1 6
8.8 1.2 1.4 56.5 31.7 0.2 22
4.5–6.6 0.6–0.9 1.1–1.3 69.3–71.4 18.8–24.0 0.1–1.2 8
4.4 0.1 0.5 66.3 28.6 0.1 7
3.5–4.1 2.0–2.1 69.3–73.4 20.0–23.2 17
4.6–5.0 0.2–0.3 66.6–71.8 23.1–27.7 23
6.2 1.7 0.4 60.3 31.4 24
6.2 0.6 0.8 72.9 19.5 26
4.8 0.7 0.8 62.1 31.6 25
6.1–8.6 1.0–2.0 1.2–2.0 58.3–66.5 24.7–31.6 14
a
These data represent a number of cultivars.
TABLE 5
Properties of Apricot Kernel Oil
a
Specifi
c gravity (g/cm
3
)
Refractive index (20
°
C)
Iodine value
Saponifi
cation number Unsponifable matter (%) Reference
0.876–0.879 1.471–1.472 90–101 189.7 0.86 10
0.914
1.464
104 193.5–199.0 7
104 0.30–1.58 29
105–113 0.56–0.80 4
0.919
92–94
187.3–187.7
0.10–1.00
28
0.931–0.932
1.480
105
8
a
These data represent a number of cultivars.
TABLE 6
Vitamin and Mineral Content of Apricot Kernels
a
(mg/100 g)
Na K Ca Mg Fe Zn Mn Ni Co Thiamin Riboflavin Niacin Vitamin C α-Tocopherol δ-Tocopherol Reference
35.2
570
1.8
290
2.82
2.33 0.48 0.14 0.002 30
0.12–0.38
0.18–0.26
2.03–6.07 1.05–2.14
36.8 473 2.4 113 2.14 3.15 14
5.8 32.2 27
1.07–7.49 1.18–4.24 8
a
These data represent a number of cultivars.

(31), is present in almond kernels reportedly at about 2–3%
b
y weight (32). Another report indicated that amygdalin con-
tent is very high (5.5 g/100 g) in bitter apricot cultivars and is
n
ot detected in the sweet ones (15).
Kernels of the wild apricot contain a high concentration of
HCN (200 mg/100 g), whereas domestic bitter apricot culti-
vars contain relatively low levels of HCN (11.7 mg/100 g)
(33). The HCN content has been found to be 11.7 (33) and 8.9
mg/100 g (34). Excess consumption of apricot kernels (to pro-
duce over 1 mg/L –CN in blood) may cause poisoning. The
fatal dose of HCN has been reported as 0.5 mg/g (35).
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[Received April 15, 2005; accepted February 6, 2006]
M. Alpaslan* and M. Hayta
Inönü University,
Department of Food Engineering,
44069, Malatya, Turkey
*To whom correspondence should be addressed.
E-mail: malpaslan@inonu.edu.tr
LETTER TO THE EDITOR 471
JAOCS, Vol. 83, no. 5 (2006)