Department of Food Science and Technology, University of California Davis, Davis, California, USA.
J Food Sci. 2024 May;89(5):2730-2746. doi: 10.1111/1750-3841.17042. Epub 2024 Mar 27.
Walnuts undergo rigorous grading before being sold to customers. There are multiple parameters used for the grading, including skin lightness. Walnuts with light skin receive superior grades while walnuts with dark skin are given poor grades or even rejected. However, information on the quality and physicochemical properties of walnuts with varying skin lightness levels is minimal. Therefore, we studied the quality of kernels of varying skin lightness from three common cultivars grown in California, USA (Chandler, Howard, and Tulare). The samples were subjected to size and weight, fat content, free fatty acid, peroxide value, oxidative stability, volatiles, tocopherols, fatty acid profile, and phenol measurements. The dark kernels had significantly lower weight and fat content, higher oxidative stability, and more volatiles than their light counterparts. The dark kernels had higher concentrations of some phenolics but low procyanidin B1 and non-existent epicatechin gallate, compared to the light kernels, indicating that these two phenolics were likely involved in an antioxidant mechanism. Oxidation and depletion of epicatechin gallate likely contributed to the darkening of walnut color.
核桃在出售给客户之前要经过严格的分级。分级使用的参数有很多，包括果皮颜色。颜色浅的核桃获得较高的等级，而颜色深的核桃则获得较差的等级，甚至被拒绝。然而，关于不同果皮颜色核桃的质量和理化特性的信息却很少。因此，我们研究了来自美国加利福尼亚州三种常见品种（钱德勒、霍华德和图莱里）不同果皮颜色的核桃仁的质量。对这些样品进行了大小和重量、脂肪含量、游离脂肪酸、过氧化物值、氧化稳定性、挥发性成分、生育酚、脂肪酸组成和酚类物质的测量。深色核桃的重量和脂肪含量明显较低，氧化稳定性较高，挥发性成分也比浅色核桃多。与浅色核桃相比，深色核桃中一些酚类物质的浓度较高，但原花青素 B1 和没食子儿茶素没食子酸酯的浓度较低，表明这两种酚类物质可能参与了抗氧化机制。没食子儿茶素没食子酸酯的氧化和消耗可能导致核桃颜色变暗。
