Abstract: Walnut skin color is one of the most important quality parameters for walnut grading. In this paper, the effects of walnut skin color and its removal by blanching on the color, nutritional composition and stability of pressed walnut oil were studied. The results showed that oil color was not significantly affected by walnut skin color (P > 0.05) and was not affected at all by peeling treatment. In the case of nutritional composition, there were no significant differences in unsaturated fatty acids, total phenolics or tocopherols between dark-colored and light-colored walnut oils; although the peeling treatment had no obvious effect on unsaturated fatty acids, but it decreased total tocopherols by 20.19% and 16.33% in the darkcolored and light-colored oils, respectively. The content of total phenolics was quite low in dark-colored and light-colored oils obtained from unpeeled walnuts and most of the phenolics were remained in meals. With respect to stability, no significant difference was found between the two oils; after peeling, the oxidation induction periods of the dark-colored and light-colored oils decreased by 0.68 and 0.53 h, respectively, and the shelf lives of 60 ℃ decreased by 5.52 and 3.36 h, respectively. In addition, it was found that the oil yield during pressing was improved by the presence of walnut skin; after peeling, the oil yields from dark-colored and light-colored kernels decreased by 5.43% and 3.29%, respectively.

Key words: walnut, skin, color, unsaturated fatty acid, total phenolics, tocopherols, shelf life