Department of Food Engineering, Faculty of Engineering, Pamukkale University.
J Oleo Sci. 2021;70(5):615-632. doi: 10.5650/jos.ess20266.
The skin of the walnut kernels can get dark during the pre- and post-harvest stages of the production. Dark kernels are less palatable for most consumers but are still edible and maybe preferable, especially in the ground form, for industrial use. In this study, we investigated the differences between oil oxidation indexes, fatty acid and tocopherol compositions of the oils, total polyphenol contents and antioxidant capacities of the extracts of light and dark walnuts. In addition, we evaluated the effects of packaging under nitrogen and vacuum-packaging techniques and storage temperature on these characteristics of both light and dark walnuts during storage for 6 months. Peroxide values and free fatty acid contents of all samples were higher at the end of storage compared to initial values, being more noticeable at 20°C than at 4°C. Increases in the free fatty acid contents were quite higher in dark walnuts than the light ones (6.1 and 3.1 fold, respectively) and the highest values of conjugated diene and peroxide were determined in the samples packaged under air and stored at 20℃. Dark walnuts had lower total phenolic, α- and γ-tocopherol contents and antioxidant activities compared to the light ones. Total phenolic and tocopherol contents decreased over time. We conclude that due to the antioxidant compounds in the fruit, oxidation parameters of dark walnuts are still acceptable at the end of 6-month storage even in the packages with air and at non-refrigerated conditions.
核桃果仁的果皮在生产的收获前后阶段会变深。深色的果仁对大多数消费者来说不太可口，但仍然可以食用，对于工业用途来说，尤其是磨碎后，可能更受欢迎。在这项研究中，我们研究了浅色和深色核桃油的氧化指数、脂肪酸和生育酚组成、总多酚含量和提取物抗氧化能力的差异。此外，我们评估了氮气包装和真空包装技术以及储存温度对这两种核桃在 6 个月储存期内这些特性的影响。与初始值相比，所有样品在储存期末的过氧化物值和游离脂肪酸含量都更高，在 20°C 时比在 4°C 时更明显。与浅色核桃相比，深色核桃的游离脂肪酸含量增加更高（分别为 6.1 和 3.1 倍），在空气包装和 20℃储存的样品中，共轭二烯和过氧化物的最高值最高。与浅色核桃相比，深色核桃的总酚、α-和γ-生育酚含量和抗氧化活性较低。总酚和生育酚含量随时间推移而下降。我们得出结论，由于果实中的抗氧化化合物，深色核桃的氧化参数在 6 个月储存期末仍然可以接受，即使在有空气的包装中和非冷藏条件下也是如此。
