Physicochemical properties, fatty acid and mineral content of some walnuts (Juglans regia L.) types

doi:10.4236/as.2010.12009

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Vol.1, No.2, 62-67 (2010)

doi:10.4236/as.2010.12009

Agricultural Sciences

Physico-chemical properties, fatty acid and mineral

content of some walnuts (Juglans re g i a L.) types

Mehmet Musa Özcan1*, Cesari İman2, Derya Arslan1

1Department of Soil Science, Faculty of Agriculture, University of Selçuk, Konya, Turkey; *Corresponding Author: mozcan@selcuk.edu.tr

2Food Engineering, Kırşehir, Turkey

Received 12 June 2010; revised 28 June 2010; accepted 13 July 2010.

ABSTRACT

Some physical and chemical properties, mineral

content and fatty acid compositions of kernel

and oils of several walnut types (Büyük Oba,

Kaman-2, Kaman-5) were determined. The oil

yields from these kernels changed between

61.4% to 72.8%. The crude fibre contents of ker-

nels ranged between 3.77% and 3.80%. In add-

ition, crude protein contents of kernels ranged

between 7.05% and 8.10%. While the peroxide

values of kernel oils change between 3.18 meq/

Kg and 3.53 meq/Kg, acidity values ranged be-

tween 0.35% and 0.56%. The main fatty acids of

walnut kernel oils were oleic, linoleic, linolenic

and palmitic acids. Linoleic acid contents of ker-

nel oils varied between 49.7% and 55.5%. On the

other hand, oleic acid contents ranged between

20.5% and 26.4%. As a result, the present study

showed the walnut kernels of the researched

species of walnut kernels from Turkey are a

potential source of valuable oil which might be

used for edible and other industrial applica-

tions.

Keywords: Walnut; Kernel; Oil; Fatty Acid

Composition; Mineral Contents

1. INTRODUCTION

Walnut (Juglans regia L) a member of Juglandaceae

family is one of the finest nuts of temperate regions. It is

the oldest cultivated fruit in the world and grown spon-

taneously almost all over Turkey. Fifty percent of pro-

duction is consumed on- form and the remainder is mar-

keted [1-3].

Ripe walnuts are mostly eaten as dessert nuts or used

in cakes, desserts and confectionery of all kinds from ice

cream to Baklava. The walnut plant has a high nutria-

tional value and high quality wood. In turkey, walnut has

a special value in Turkish foods and is very common in

traditional Turkish foods [2]. Although walnuts are rich

in fat, a diet supplemented with walnuts had a beneficial

effect on blood lipids, lowering blood cholesterol and

lowering the ratio of serum concentrations of low deroity

lipoprotein: high density lipoprotein by 12% [4,5]. Oil

contents of walnut kerrels can generally vary from 52 to

70 % depending on the cultivar, location grown and irri-

gation rate [2,3,6-8]. Most nuts are rich in manounsatu-

rated fat (oleic acid) while walnuts are also high in two

polyunsaturated fatty acids linoleic acid and α-lino-

lenic acids. The major fatty acids found in walnut oil are

oleic, linoleic and linolenic acids [3,5,8]. The fatty acid

profile of walnut oil varies between cultivars. It is im-

portant to a identify these differences in locally grown

cultivars and to identify which fatty acids give the best

nutritional qualities [8,9]. Some fruit seeds such as

cherry, apricot, citrus and apple can be used as sources

of oils. Some seed oils are already used for several pur-

poses: blending with highly saturated edible oils to pro-

vide new oils with modified nutritional values as ingre-

dients in paint and varnish formulations, surface coatings

and oleo-chemicals, and as oils for cosmetic purposes

[10].

The aim of this study was to determine their physical

and chemical properties, mineral contents and fatty acid

composition of some walnut types collected from Kırşe-

hir province in Turkey.

2. MATERIAL AND METHOD

2.1. Material

The kernels of some walnut cultivars (Büyük Oba, Ka-

man-2, Kaman-5) were obtained by hand processing

from walnuts growing in Kırşehir province of Turkey in

August 2008. Kernels were kept in glass jars until

analyses at refrigerator. In all stages of trials, dry and

mature kernels have been used.

M. M. Özcan et al. / Agricultural Sciences 1 (2010) 62-67

2.2. Physical Analyses

Shelled weights of walnuts: It was used 25 unit walnut

for each walnut variety. Each walnut was weighted

separately, and average hulled fruit weights for each one

were found.

Shelled diameters of walnuts: Mean diameter of

each hulled walnut was measured by using electronic

cumpas.

Yields of walnuts: Five walnut were used for yield

analysis of each walnut. Yield was calculated as the per-

centage rate to the shelled walnut fruit of kernel weight.

Determination of dry matter: Air dried and ground

walnut samples were waited in incubator calibrated to

105℃ for 24 h, and about 10 g samples from each dried

walnut was weighted.

2.3. Chemical Analyses

The some chemical compositions (crude oil, crude pro-

tein, crude fiber, and crude ash, acidity, peroxide value,

refractive index and saponification value) were analyses

according to AOAC [11]. For oil analyses, each samples

was homogenized and subjected to extraction for 6 h

with petroleum ether (boiling range 30-60℃) in a Sox-

hlet apparatus. The extracted oil was dried over anhy-

drous sodium sulphate and the solvent was removed

under reduced pressure in a rotary film evaporator. Oil

percentages were determined by weight difference. Ash

was determined in a muffle furnace at 900℃ for 8 h

[11]. The nitrogen content estimated by the Kjeldahl

method and was converted to protein content by using

the conversion factor 6.25.

2.4. Determination of Fatty Acids

Fatty acid composition for walnut kernel samples were

determined using a modified fatty acid methyl ester

method as described by Hışıl [12]. The oil was extracted

three times for 2 g air-dried seed sample by homogeni-

zation with petrolium ether. The oil samples (50-100 mg)

were converted to its fatty acid methyl esters (FAME).

The methyl esters esters of the fatty acids (1 µl) were

analysed in a gas chromotography (Shimadzu GC-2010)

equipped with a flame ionising detector (FID), a fused

silica capillary column (60 m × 0.25 mm i.d.; film

thickness 0.20 mikrometere). It was operated under the

following conditions: oven temperature program. 90℃

for 7 min. Raised to 240℃ at a rate 5℃/min and than

kept at 240℃ for 15 min); injector and detector tem-

peratures, 260 and 260℃; respectively, carrier gas. ni-

trogen at flow rate of 1.51 ml/min; split ratio 1/50 µl/min.

A Standard fatty acid methyl ester mixture (Sigma

Chemical Co.) was used to identify sample peaks. Com-

mercial mixtures of fatty acid methyl esters were used as

reference data for the relative retention times [13]. Qua-

ntitative analyses of the fatty acids were performed using

the heptadecanoic acid methyl ester as internal standard.

The results are mean values of three replicates.

2.5. Determiation of Mineral Contents

About 0.5 g of dried and walnut kernels were put into

burning cup with 15 ml of pure NHO3. The sample was

incinerated in a MARS 5 microwave oven (CEM corpo-

ration Manufactura) at 200℃. Distilled deionized water

and ultrahigh-purity commercial acids were used to pre-

pare all reagents, standards and walnut kernel samples.

After digestion treatment, samples were filtrated through

whatman No 42. The filtrates were collected in 50 ml

Erlenmayer flasks and analysed by ICP-AES (Varian).

The mineral contents of the samples were quantified

against standard solutions of known concentrations which

were analysed concurrently [14].

Working conditions of ICP-AES:

Instrument: ICP-AES (Varian-Vista

RF Power: 0.7-1.5 kw (1.2-1.3 kw for Axial)

Plasma gas flow rate (Ar): 10.5-15 L/min. (radial) 15

(axial)

Auxilary gas flow rate (Ar): 1.5

Viewing height: 5-12 mm

Copy and reading time: 1-5 s (max. 60 s)

Copy time: 3 s (max. 100 s)

2.6. Statistical Analyses

Results of the research were analysed for statistical sig-

nificance by analysis of variance [15]. This research was

performed by three duplicates with a replicate.

3. RESULTS AND DISCUSSION

The physical and chemical properties of some walnut

varieties (Büyük Oba, Kaman-2, Kaman-5) collected from

Kırşehir province in Turkey are given in Table 1. The

weight with hull, diameter, hull weight, kernel weight,

yield, dry matter, crude fibre, crude ash, crude protein,

crude oil, saponification, refraxtive index, acidity, per-

oxide value of walnut kernels were determined. Accord-

ing to variance analyses, important differences were

found between physical properties and their weighs and

kinds as statistical, p < 0.01 level.

The oil yields of kernels varied from 53% (Büyük

Oba and Kaman-5) to 60% (Kaman-2 cv) of the dry

weight. The oil contents of kernels changed among the

varieties to more than about 60% of each. However, be-

cause of economical value of the oil, these kernels could

be used as potential sources of oils. Büyükoba cultivar

had the highest oil (72.87%) content, followed by Ka-

man-5 cv (72.13%) and Kaman-2 cv (61.38%). The

M. M. Özcan et al. / Agricultural Sciences 1 (2010) 62-67

Table 1. Some physical and chemical properties of walnut kernel and oils.

Walnut types

Properties Kaman–5 Büyük Oba Kaman–2

Weight with shelled (g) 12.96 ± 1.00 b 15.74 ± 0.02 a 13.6326 ± 0.03 b

Diameter with shelled (mm) 36.72 ± 1.22 b 41.02 ± 0.98 a 39.79 ± 0.9 a

Shell weight (g) 6.6882 ± 0.01 a 7.7585 ± 0.0005 a 4.3256 ± 0.01 b

Kernel weight (g) 7.815 ± 0.005 8.9289 ± 0.02 6.5872 ± 0.0198

Yield (%) 53 ± 0.4 b 53 ± 2 b 60 ± 2.5 a

Drt matter (%) 99.58667 ± 0.015275 98.58333 ± 1.440498 99.58 ± 0.04359

Crude oil (%) 72.13 ± 4.681047 72.865 ± 8.619632 61.375 ± 10.3450

Peroxide value (meq O2/kg) 3.5294 ± 0.0004 3.1849 ± 0.0999 3.4482 ± 0.0103

Crude fiber (%) 3.90 ± 0.60 3.77 ± 0.32 3.87 ± 0.31

Acidity (%) 0.5628 ± 0.0101 0.35 ± 0.015 0.5575 ± 0.01015

Saponification value 114.60 ± 0.01 a 106.96 ± 0.01 b 102.09 ± 1.00 c

Ash (%) 1.985 ± 0.431335 1.71 ± 0.028284 2.525 ± 1.15259

Crude Proteina (%) 8.10125 ± 0.055225 7.0489 ± 1.099834 7.24155 ± 1.878

Refractive index (nD20) 1.535 ± 0.0005 1.534 ± 0.00005 1.537003 ± 0.0001

aNx6.25

crude fibre contents ranged between 3.77% (Kaman-5 cv)

and 3.90% (Büyükoba). While crude ash contents chan-

ged between 1.99% (Kaman-5 cv) and 2.53% (Kaman-

2), crude proteins of kernels ranged between 7.05 %

(Büyükoba cv) to 8.10% (Kaman-5 cv). In addition,

kernel weights changed between 6.59 g/unit (Kaman-2

and 8.93 g/unit (Büyükoba cv). These results are com-

parable to data previously reported in the literature

[7,16]. Nuts and oils intended to be cooked may require

a low polyunsaturated fatty acid content [17].

Some physical and chemical properties of walnut

kernels and oils are given in Table 1. According to vari-

ance analyses, differences between varieties to saponifi-

cation values were found statistically important at the p

< 0.01 level. While the peroxide values of kernel oils

change between 3.18 (Büyükoba) and 3.53 meq/Kg (Ka-

man-5 cv), acidity values ranged between 0.35% (Büyü-

koba cv) and 0.56% (Kaman-5 and Kaman-2). Refrac-

tive index was determined between 1.534 (Büyükoba)

and 1.537 (Kaman-2 cv). In addition, saponification val-

ues of kernel oils were measured between 102.09 (Ka-

man-2 cv) and 114.60 (Kaman-5 cv). Differences among

the values of walnut varieties can probably be because of

growing conditions, climatic, environmental conditions

and analytic conditions.

Fatty acid compositions of walnut kernel oils are

given in Table 2. Results showed that the oils of all va-

Table 2. Fatty acid composition of walnut oils (%).

Walnut types

Fatty Acids Kaman-5 Büyük Oba Kaman-2

Palmitic

(C16:0) 6.5 6.3 6.3

Stearic

C18:0) 2.6 2.5 2.6

Oleic

(C:18:1) 26.4 22.2 20.5

Linoleic

(C18:2) 49.7 53.6 55.5

Linolenic

(C:18:3) 14.3 14.5 14.8

rieties used in this experiment had higher linoleic and

oleic acid contents. Linoleic acid contents of kernel oils

ranged between 49.7% (Kaman-5 cv) and 55.5% (Ka-

man-2 cv). The proportions of the most abundant fatty

acids (linoleic acid) of the kernel oils varied among dif-

ferent varieties. This proportion was also higher than

that in other fruit seed oils; mahaleb (35.4%), cherry

laurel (53.7%), date pit (49.54%), walnut (13.8-33.0%)

[8,18-20]. Stearic and palmitic acids are the main satu-

rated components in all walnut cultivars. Palmitic acid is

differed in the different walnut cultivars. Its percentage

was found between 6.3% (Kaman-5) and 6.3% (Büyükoba

and Kaman-2). These results are in good agreement with

M. M. Özcan et al. / Agricultural Sciences 1 (2010) 62-67

in fatty acid composition for several walnut kernels

[2,3,5,6-8]. Our results are similar in fatty acid composi-

tion when compared to the values in the literature.

Palmitic, stearic, oleic, linoleic and linolenic acid con-

tents of walnut oil were established as 7.22%, 1.07%,

28.51%, 52.46% and 10.50%, respectively [221]. Özkan

and Koyuncu [3] found that the contents of the main

fatty acids of walnut genotypes were 5.24-7.62% palmitic,

2.56-3.67% stearic, 21.18-40.20% oleic, 43.94-60.12%

linoleic and 6.91-11.52% linolenic. Zwarts et al. [8] re-

ported as 6.7-8.2% palmitic, 1.4-2.5% stearic, 13.8-33.0%

oleic, 49.3-62.3% linoleic and 8.0-14.2% linolenic acids.

The oleic acid content of walnut oil was lower than that

of walnut oil reported by Zwarts et al. [8], Özkan and

Koyuncu [3] and Koyuncu and Aşkın [22]. The walnut

fatty acid composition shows high contents of linoleic

acid and linolenic acid which are beneficial to human

health and linoleic acid and especially linoleinic acid

play important roles for human health regarding the

cardio vascular system [3,4,22].

The mineral contents of walnut kernels were deter-

mined by ICP-AES. The mineral compositions of ker-

nels were summarized in Table 3. Mineral elements

were found to vary widely depending on different walnut

cultivar kernels. According to variance analyses, differ-

ences between walnut cultivars to Ca, Cu, Fe, K, Mg,

Mn, Na and P were found statistically important at p <

0.01 level.

Ca, K, Mg, Na and P contents of all the walnut culti-

var kernels were generally found very high. In addition,

other minerals were determined very low. The levels of

Ca of samples ranged between 2462.3 mg/Kg (Büyükoba

cv) and 2757.9 mg/Kg (Kaman-5 cv), K contents were

determined between 3478.8 mg/Kg (Büyükobacv) and

5476.2 mg/Kg (Kaman-5). While Mg contents are estab-

lished between 4163.4 mg/Kg (Büyükoba cv) and 5488.1

mg/Kg (Kaman-2 cv), P contents of kernels were found

between 2226.2 mg/Kg (Büyükoba cv) and 2604.3

mg/Kg (Kaman-2 cv). Walnut kernels were found to be

rich in some minerals such as Ca (1108.6 mg/kg), K

(4627.6 mg/kg), P (3621.9 mg/kg), Na (44.7 mg/kg) Mn

(46.3 mg/kg and Mg (1089.9 mg/kg) [23]. Çağlarırmak

[2] reported as 280-380 mg/100 g P, 230-340 mg/100 g

K, 81-99 mg/100 g Mg and 67-105.5 mg/100 g Ca in

fresh walnut kernels. Our results were found differences

compared with mineral values reported by Çağlarırmak

[2]. These differencies of cultivars minerals may be due

to growth conditions, varieties, genetic factors, harvest-

ing time, soil properties, geographical variations and

analytical procedures [2,24]. Calcium is the major com-

ponent of bone and assists in teeth development [25].

Other elements which may contribute to biological

processes, but which have not been established as essen-

tial are barium, cadmium [24]. The high quantity of po-

tassium, phosphorus, magnesium, and calcium, together

with the small proportion of sodium plus the content of

Table 3. Mineral contents of walnut kernels (mg/Kg)b.

Walnut types

Minerals Kaman–5 Büyük Oba Kaman–2

B 15.114 ± 1.503b C 11.985 ± 2.001 13.057 ± 1.107 C

Ca 2757.883 ± 10.436 B 2462.315 ± 76.754 D 2637.618 ± 37.460 B

Cr 1.695 ± 0.360 C - - 3.323 ± 2.820 C

Cu 5.676 ± 1.099 C 9.333 ± 0.801 E 5.944 ± 0.325 C

Fe 18.584 ± 1.542 C 17.875 ± 1.252 E 21.815 ± 3.514 C

K 5476.201 ± 663.718 Aa 3478.757 ± 482.96 Ab 5380.995 ± 160.96 Aa

Mg 4375.513 ± 925.221 A 4163.363 ± 368.281 B 5488.101 ± 218.072 A

Mn 21.991 ± 4.977 C 22.201 ± 1.413 E 17.585 ± 0.134 C

Mo - - - - 1.671 ± 0.537 C

Na 617.713 ± 65.545 C 667.416 ± 74.322 D 833.433 ± 26.601 C

Ni 1.651 ± 0.774 C - - 1.915 ± 4.564 C

P 2241.411 ± 653.820 B 2226.221 ± 230.554 C 2604.255 ± 45.318 B

Zn 17.981 ± 0.523 C 20.623 ± 1.185 E 18.353 ± 4.206 C

aDryweight; bmean±standard deviation

M. M. Özcan et al. / Agricultural Sciences 1 (2010) 62-67

the essential elements as iron, manganese, copper, and

zinc and allows the apricot, as well as the almond, to be

considered as an excellent source of bioelements [26].

4. CONCLUSIONS

The accurate quantification of these analyses has very

important applications for the nutrition sciences, because

fatty acids, protein, oil and mineral contents in particular

seed have a very important effect on health. These re-

sults of the experiment presented have shown that apri-

cot cultivars have some distinctive chemical and physic-

cal properties, fatty acid and mineral content profiles.

Kernels in apricot varieties can be good source oil due to

their abundance in the kernels and their high oil content.

Such utilization of apricot fruits processing wastes could

provide extra income and at the same time help mini-

mize a waste disposal problem. The mineral contents of

apricot cultivar kernels collected from Malatya province

of Turkey were established by ICP-AES. The contents of

most minerals such as Ca, K, Mg and P are at adequate

levels. Mineral elements were found to vary widely de-

pending on different apricot kernels. Apricot kernels

were found to be important sources of nutrients and es-

sential elements. In addition, it is apparent that apricot

kernels are good sources of micro and macro minerals,

and consumed as a food ingredient to provide the human

nutrient.

In this study, Kaman walnut varieties have got stan-

dard walnut properties. When these varieties were grown

modified conditions, it was estimated to be having more

quality. While walnuts have about 13.2 g fruit weight, 38

mm diameter with hull, 6.5 g hull weight, 7 g kernel

weight, 55% yield due to physical properties, as a

chemical properties walnut contained 98% dry matter,

65% crude oil, 2% ash, 7.4% crude protein and 3.75%

crude fiber. The oils of walnut varieties are more yel-

lowish-clear. Mean peroxide value, free fatty acidity,

density, saponification value, refractive index values are

3.2 meq/kg, 0.4%, 13.9 g/ml, 107.5, 1.535 nD, respect-

tively. The major fatty acids of walnut oils were estab-

lished as 6.4% palmitic, 2.5% stearic, 23% oleic, 51.5%

linoleic and 14.4% linolenic. The highest minerals were

Ca, Mg, K and P. Walnut is one of important foods need

found in daily diets. High polyunsaturated fatty acid

contents are the most important properties. At the same

time, due to walnut’s nutrition important was thought to

be found between strategic foods in future.

5. ACKNOWLEDGEMENTS

This work was supported by Selçuk University Scientific Research

Project (S.U.-BAP. Konya-Turkey).

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