Fatty acid compositions and tocopherol concentrations in the oils of 11 varieties of walnut (Juglans regia L.) grown at Xinjiang, China

SUMMARY To confirm the fatty acid compositions and tocopherol concentrations in walnut oil, 11 varieties of walnut (Juglans regia L.) were collected from the Jackwood Experiment Station, Xinjiang Academy of Forestry during harvest in 2010, 2011, and 2012. Total oil was extracted, and the total fatty acid composition of each oil, including saturated fatty acids (SFA), unsaturated fatty acids (UFA), mono-unsaturated fatty acids (MUFA), and poly-unsaturated fatty acids (PUFA), were analysed by gas chromatography, while tocopherol concentrations were measured by high-performance liquid chromatography. The results showed that the total UFA content was > 91% (w/w) in all 11 varieties of walnut. Linoleic acid (18:2) was the dominant UFA, varying from 57.6% (w/w) in ‘XJ020’ to 67.7% (w/w) in ‘XJ004’, whereas concentrations of linolenic acid (18:3) ranged from 9.7% (w/w) in ‘XJ017’ to 19.2% (w/w) in ‘XJ020’. Compared to all other walnut varieties, ‘XJ020’ had the highest concentration of total UFAs [93.7% (w/w)]. Moreover, tocopherol concentrations ranged from 0.04–0.34 mg ml−1 in the walnut oils. γ-Tocopherol was dominant and ranged from 0.033–0.328 mg ml−1, while δ-tocopherol accounted for 0.006–0.038 mg ml−1. No α-tocopherol was detected in any walnut oil. This work contributes to our knowledge on the nutritional properties of walnut oils and will assist in the selection of walnut varieties for a healthy diet.