Increasing oxidative stability of walnut kernel by whey protein isolate coating

Walnut kernel browning and oil oxidation are two major problems during walnut’s storage. The aim of this study was application of suitable coatings for delaying these reactions. For this purpose whey protein isolate/glycerol coatings at three ratio 50:50, 60:40 and 70:30 in two forms denatured and non-denatured (heated or not) were used for coating walnut kernels. The effects of whey protein isolate/glycerol coatings on lipid oxidation, acidity, and sensory evaluation of walnut kernels during four months storage were studied. The most effective inhibition of lipid oxidation was obtained through coatings with higher concentration of whey protein isolate and denatured. In acidity, texture, color, and glossiness property no significant difference observed between the coated kernels. But in flavor, the samples coated with whey protein/glycerol at 70:30 ratio in denatured form showed significantly more acceptable than 50:50 and 60:40 non denatured coatings. The results showed that WPI: Gly at 70:30 ratio coating could increase the shelf life of walnut kernel more than other coatings.