Oil composition in stored walnut cultivars—quality and nutritional value

Abstract

The effects of temperature and O2 availability on quality attributes and nutritional value of oil in four walnut (Juglans regia L.) cultivars (Chandler, Hartley, Franquette, and Ioli) were investigated. Dried kernels, all of initial high quality, were packaged under air or N2 or CO2 and stored at 1 °C or 20 °C for 12 months. Results showed that the saturated fatty acids (SFA) myristic, palmitic, stearic, and arachidic remained stable during storage, whereas the unsaturated palmitoleic, oleic (OL), gondoic, linoleic (LL) and linolenic (LN) decreased, with the stable vaccenic being the exception. Rancidity, assessed as free fatty acids and peroxide value, increased after 12 months, and rancidity evolution found to be correlated with LL and LN, but not with OL. In all cultivars, low temperature and N2 or CO2 prevented additively the fatty acid (FA) losses and rancidity increases. The best results were obtained in walnuts stored at 1 °C under N2 or CO2, while storage at 20 °C under air led to the greatest product deterioration. However, storage at 20 °C under N2 or CO2 and at 1 °C under air showed intermediate results and similar among them. The cultivar affected the kernel oil content and FA profile initially, as well as, the FA decreases and rancidity development during storage. The omega‐6/omega‐3 ratio largely depended on cultivar and was affected by storage conditions. Overall, the storability of the studied cultivars in descending order was Chandler > Hartley, Franquette > Ioli.Practical applications: Storage at 1 °C under N2 or CO2 for 12 months retained the peroxide value (PV) lower than 3 meq O2 kg−1 oil and the free fatty acids (FFA) up to 0.6%, cut‐off values for acceptable walnuts, as suggested by the walnut industry in California. Storage at 20 °C under N2 or CO2 increased the PV value up to 10 meq O2 kg−1 oil, being the upper acceptable limit according to panel tests in studies. For energy savings, the 12‐months storage at 20 °C with low O2 availability can substitute the storage at 1 °C under air. Rancidity development and nutritional value related to fatty acids largely depended on cultivar. Thus, the cultivar factor should also be considered for storage purposes and according to the destination markets.Effects of temperature and packaging atmosphere on rancidity and nutritional value related to oil composition in stored dried kernels of walnut (Juglans regia L.) cultivars. The present results are summarized in the bi‐plot (combination of score and load plots) of Principal Component Analysis. Each color corresponds to each cultivar. Rhombuses, circles, squares, and triangles, corresponding to different storage conditions, indicate the position of each walnut sample in score plot. Daggers indicate the position of major fatty acids and indicators of rancidity in load plot.