Effect of geographic origin, variety and storage on tocopherol concentrations in walnuts by HPLC

Retinol, tocopherols and carotenes were extracted from walnut kernels. Three walnut extraction procedures were compared. Direct hexane extraction was selected. The fat-soluble vitamin separation was achieved by reversed-phase high performance liquid chromatography equipped with a ternary mobile phase gradient (methanol, butanol, water), and wavelength programming. The chromatographic run was under 35 minutes. This technique allowed a good resolution of alpha, gamma, delta tocopherols, alpha and beta carotenes and retinol. Two walnut varieties (Franquette and Hartley) from two geographical origins (France, USA) were analyzed. Retinol, and carotenes were not identified in walnuts. The amounts of alpha, gamma, delta tocopherols ranged respectively from 1.08 to 4.05, 21.78 to 26.46, and 2.51 to 4.23 (mg/100 g). Significant differences related to variety and geographical origin were observed. A decrease in tocopherols (about 30%) was observed after 3 month refrigerated storage. Copyright (C) 1996 Elsevier Science Ltd