Key chemical composition of walnut (Juglans regia. L) Oils generated with different processing methods and their cholesterol-lowering effects in HepG2 cells

We systematically evaluated fatty acids and triacylglycerol composition, as well as tocopherol, phytosterol, and phenolics, in walnut oil and compared the cholesterol-lowering effects of oil processed with different methods (cold pressing, roast-pressing, hexane extraction, subcritical butane extraction, and supercritical CO2 extraction). The different methods did not affect the lipid composition of walnut oil. The tocopherol (41.11 mg/100 g) and total phenolic content (TPC, 4.26 mg/100 g) of roast-pressed walnut oil and the phytosterol contents of subcritical butane-extracted walnut oil (106.51 mg/100 g) were higher than those of other tested oils. Walnut oil significantly decreased cholesterol synthesis by downregulating the expression of HMGCR, SREBP-2, and CYP51 genes, and increased cholesterol efflux by upregulating the expression of ABCGI, thus significantly reducing total cholesterol and triacylglycerol. Phytosterols and TPC in walnut oil were responsible for lowering cholesterol; the optimal concentration of phytosterols was 10 mu g/mL, and that of TPC was 12.5 x 10(-3) mu g/mL. Through process optimization, a new processing method for walnut oil based on biological evaluation was preliminarily established.