Effect of Packaging Technique and Storage Conditions on Walnut Kernel Quality

Abstract

In this study, the changes in some chemical characteristics of whole, crushed and ground walnut kernels packaged by different techniques (packaging under normal atmosphere, vacuum and nitrogen gas) during 21-week storage at different temperatures were investigated. In whole kernels, the levels of free fatty acids and conjugated dienes did not dramatically change and the increases in peroxide and conjugated triene values were relatively lower than those in crushed and ground samples. Packaging under nitrogen gas was effective in protecting walnuts against oxidation reactions by limiting increases in peroxide and conjugated triene values. For example, p-anisidine values, which is an indicator of the presence of aldehydes, one of the secondary oxidation products, were determined as 0.56 and 0.40, respectively, in ground walnut samples packaged under normal atmosphere and nitrogen gas and stored for 21 weeks at 20°C. The increases in free fatty acid, peroxide and conjugated diene values were lower at 4°C than those determined at 20°C. Size reductions in walnut kernels generally resulted in increase in oxidation parameters. This was demonstrated by the high values of peroxide, conjugated triene and para-anisidine, especially detected in ground samples. © 2021 by the Author(s).