Shelf life extension of walnut kernel: effect of temperature and vacuum packaging storage

Walnut is one of the most important dry fruits with high nutritional value that serves as a natural source of antioxidants. However, there have always been concerns regarding the preservation of walnut kernels due to the high oxidation. In this study, the effect of temperatures (4 celcius and 25 degrees C) and vacuum packaging (5% vacuum, and non-vacuum control) were investigated on the quality of walnut kernels of two commercial genotypes (stone and paper) during 6 month. The total phenol and flavonoid contents, and antioxidant capacity decreased, and consequentially kernel browning occurred with increased hue angle value and decreased lightness values. During the storage the activities of PPO and POD increased but the activity of CAT decreased, indicating the redox leaned to oxidation. Low temperature and vacuum packaging both slowed down the oxidative metabolism, and suppressed reduction of antioxidants, and delayed the discoloration/browning of walnut kernels.