An Approach Regarding the Walnut Oil Obtained in a Press Screw and its Quality

Abstract

The cold pressed walnut kernels oil is treasured by epicurians. The oil is important for a small segment of the market being used in the gourmet kitchen. The cold pressed oil from walnut kernels (Juglans regia L.) with a content of about 90 % of unsaturated fatty acids in the triglycerides, is a remarkable source ω-3 si ω-6 fatty acids (70 % of the oil triglycerides). The aim of the study was the processing of walnut oil from walnut kernels from the area of Cluj by cold pressing and the influence of the raw material quality upon the oil quality. Walnut kernels from the area of Cluj were used for the oil processing, two, respectively 6 months after harvesting, with a screw press of small capacity (until 5 kg oleaginous seeds/hour). Different pressing heads: 5, 6 and 7mm in diameter were tested. The efficiency of the pressing process and the productivity of the press were determined. For the raw material there were determined the water content (drying at 103±2°C) and the raw fat content (extraction with petroleum ether at 60 °C with Soxhlet extractor). The acid value, the iod value and the fatty acids profile of the triglycerides (GS-methods) were determined for the walnut kernel oil obtained by cold pressing. The naturally dried walnut kernels had water contents of 3,20 and 3,36% and fat contents of 67,14 and 66,36% (two, respectively 6 month after harvesting). The process efficiency by using the press head of 6mm in diameter (65,11 and 66,65 % walnut oil) was better compared to those obtained when the pressing heads used were 5mm (63,86 and 63,87%) and 7mm (62,97%) in diameter. The best pressing productivity was obtained by using the press head of 6 mm in diameter (1,27 kg walnut kernel/h) when walnut kernels were processed two months after harvesting. At the use of the pressing head 5 mm in diameter no big differences occurred between the press productivity values (1,02 and 1,09 kg walnut kernels/h kernels processed two, respectively 6 moths after harvesting). The acid value of the walnut oils was lower than 1,26 mg KOH/g oil, after 6 moths of cold storage, being under the accepted limit value for crude oil (4 mg KOH/g oil). The iodine value was between 127,65 and 138,68. The results of fatty acids profile of the triglyceride from the walnut oil emphasised its alimentary value (8,78 % saturated fatty acids, 19,5 % monounsaturated fatty acids, 60,87 % linoleic acid and 10,56 % linolenic acid–average values). Results were comparable to the literature data. We recommend further studies of the walnut kernels oil processing and quality and the improving of the consumer information program regarding the importance and alimentary value of the different cold pressed oils.