Effects of hulling methods on the odor, taste, nutritional compounds, and antioxidant activity of walnut fruit

In this study, the effects of four different hulling methods, included natural heaping (NH), manually hulled (MH), solid ethylene-releasing agent (SERA) and immersion in ethephon (IE), on odor, tastes, nutritional compounds (fat, protein, and fatty acids), antioxidant activities and total phenols content of green walnut were investigated. The result indicated that SERA treated group had the highest hulling rate (82.80%), followed by IE (54.84%) and NH (46.24%), however, both odor and taste of fresh walnut kernels were unpleasant in SERA and IE treatments groups. Additionally, the lowest antioxidant activity (AAC) (63.34), DPPH scavenging activity (32.63%), reducing power (0.097) and total phenols content (0.185 g kg−1) were detected in SERA group. The most pleasant sweet taste was found in MH group. Moreover, the walnut kernels treated by MH hulling method had the highest AAC (305.09), DPPH scavenging activity (79.04%), reducing power (0.335), total phenols content (0.777 g kg−1), and unsaturated fatty acids (UFAs) percentage (89.72%). The walnut kernels treated by NH method had the most pleasant odor and color. Therefore, we concluded that hulling methods had great influence on the walnut qualities. Our findings provide a new perspective on choosing hulling methods to meet the different quality demands of walnuts.