Fatty Acid Properties of Kernel Oil from Pistacia khinjuk Fruits

The Pistacia genus belongs to the Anacardiaceae family, which consists of 11 species. Three Pistacia species occur naturally in Iran, including Pistacia vera, P. atlantica, and P. khinjuk [1]. P. khinjuk grows wild in Iran and is called Kolkhoung in the Persian language. The Kolkhoung population covers an area as large as 700,000 hectars, stretching from south and southwest to central and eastern parts of the country [2]. The fruit of P. khinjuk is used by the natives as food after grinding and mixing with other ingredients [3]. P. khinjuk fruit is composed of kernel, wooden rough shell, and soft outermost hull which constitute 37%, 26%, and 37% of the fruit, respectively [2]. Oil extraction efficiency of kernel is more than 60% [4]. A study of the fatty acid composition of the kernel oil from P. khinjuk has not been done previously, but in previous studies the chemical composition of the P. khinjuk fruit and P. khinjuk hull oils was investigated. The fatty acid composition of the oil from P. khinjuk fruit showed that the amounts of oleic, palmitic, linoleic, palmitooleic, stearic, and linolenic acids were 52.12, 17.82, 17.44, 5.73, 2.31, and 1.5%, respectively [5]. The major fatty acids of hull oil from P. khinjuk were oleic acid, palmitic acid, linoleic acid, palmitoleic acid, stearic acid, and linolenic acid, too [6]. Therefore, this study was undertaken to investigate the fatty acid composition of P. khinjuk kernel oil (PKKO) and to compare its properties with those of P. khinjuk hull oil (PKHO) used as the control.

The main fatty acid found in PKKO and PKHO was oleic acid, and there was a significant difference in amounts of it between the two studied oils. The amount of linoleic acid in PKKO was more than that in PKHO, but the percent of palmitic and palmitoleic acids in PKKO was lower than that in PKHO. The linolenic acid contents in PKKO and PKHO were statistically the same, too.

Based on the composition of the fatty acids, PKKO had a higher food value than PKHO. The essential fatty acids (linoleic and linolenic acids) of PKKO and PKHO were 24.11 and 13.52%, respectively. It was also found that the ratio between polyunsaturated to saturated fatty acids (PUFA/SFA) (0.93) and calculated oxidizability (Cox) value (3.14) of PKKO were higher than those of PKHO (0.52 and 2.14, respectively). The Cox value and PUFA/SFA of PKKO are lower than those of P. atlantica (Bene in the Persian language) kernel oil (the most similar species to P. khinjuk with a highly stable oil) and sesame oil (one of the most stable oils) [2, 7]. Therefore, it can be expectable that PKKO has a high oxidative stability.

The fatty acid composition of PKKO and PKHO indicates that the fatty acids in these oils are statistically different. From the viewpoint of nutritional value, PKKO is a good oil. The oxidative stability of PKKO is probably good, too.

Plant Material. The fruit sample of P. khinjuk was collected from the field in Meymand in Fars Province, and our sample was stored at –18°C until analysis.

Extraction. After drying in the shade, the wooden rough shell and soft outermost hull of the P. khinjuk fruits were separated from the kernels. The soft hull and kernel were ground to powder in a grinder. To begin the extraction procedure, the prepared powder was mixed with hexane solvent in 1:4 ratio and put in a shaker incubator in the dark at room temperature for 48 h. To remove the solvent, the solution was then incubated under vacuum conditions and 40°C for 6–12 h [8].

Gas-Liquid Chromatography. The fatty acid profile of the oils was determined by gas-liquid chromatography and reported in relative area percentages. The fatty acids were transesterified into their corresponding FAMEs by vigorous shaking of a solution of the oil in hexane (0.3 g in 7 mL) with 2 mL of 7 M methanolic potassium hydroxide at 50°C for 10 min. The FAMEs were identified using an HP-5890 chromatograph (Agilent, Palo Alto, CA) equipped with a CP-FIL 88 (Supelco Inc., Bellefonte, PA) capillary-fused silica column (60 m × 0.22 mm I.D., 0.2 mm film thickness) and a flame ionization detector. Nitrogen was used as a carrier gas with a flow rate of 0.75 mL/min. The oven temperature was maintained at 198°C, and that of the injector and the detector at 250°C.

Statistical Analysis. All experiments and measurements were carried out in triplicate, and data were subjected to analysis of variance (ANOVA). ANOVA and regression analyses were performed using MStatC and SlideWrite software. Signicant differences between means were determined by Student′s t-test; p values of less than 0.05 were considered statistically significant.