Grilo Filipa S, Wang Selina C
Department of Food Science and Technology, University of California, Davis, CA 95616, USA.
Olive Center, Robert Mondavi Institute for Wine and Food Science, University of California, Davis, CA 95616, USA.
Foods. 2021 Feb 4;10(2):329. doi: 10.3390/foods10020329.
Kernel oxidation susceptibility and pellicle darkening are among the biggest concerns regarding walnut quality. Monitoring oxidation is crucial to preserve quality from production to consumption. Chemical oxidation parameters (peroxide value and UV absorbances), fatty acid profile, tocopherols, phenols, and volatiles in 'Chandler' and 'Howard' kernels were studied at different time points during 28 weeks of storage to evaluate potential oxidation markers. During storage, peroxide value, UV absorbances, and volatiles concentration increased; oxidative stability, phenols, and tocopherols decreased, while fatty acid profile was unaffected. 'Chandler' had a lower peroxide value, K, and K; and higher kernel and oil oxidative stability compared to 'Howard'. Phenols and tocopherols decreased 1.2-fold in 'Chandler' and 1.3-fold in 'Howard'. Using multivariate analysis, samples were discriminated in three groups according with their oxidative levels. Increases of volatiles in oil and kernel were associated with higher oxidative levels. Pentanal, 2-methylpropanal, hexanal, -2-pentenal, 3-octanone, octanal, -2-penten-1-ol, hexanol, -2-octenal, 1-octen-3-ol, benzaldehyde, -2,4-nonadienal, and hexanoic acid in kernels were adequate at distinguishing oxidation levels and as oxidative markers in walnuts. Kernel volatiles is a useful measurement for walnut oxidation during storage without any prior fat extraction.
果仁氧化敏感性和种皮变黑是核桃品质方面最令人担忧的问题。监测氧化对于从生产到消费的质量保持至关重要。研究了‘钱德勒’和‘霍华德’果仁在储存28周期间不同时间点的化学氧化参数（过氧化值和紫外线吸光度）、脂肪酸谱、生育酚、酚类和挥发性物质，以评估潜在的氧化标志物。在储存期间，过氧化值、紫外线吸光度和挥发性物质浓度增加；氧化稳定性、酚类和生育酚减少，而脂肪酸谱未受影响。与‘霍华德’相比，‘钱德勒’的过氧化值、K和K较低；果仁及油脂的氧化稳定性较高。‘钱德勒’中的酚类和生育酚减少了1.2倍，‘霍华德’中减少了1.3倍。使用多变量分析，根据氧化水平将样品分为三组。油脂和果仁中挥发性物质的增加与较高的氧化水平相关。果仁中的戊醛、2-甲基丙醛、己醛、反-2-戊烯醛、3-辛酮、辛醛、反-2-戊烯-1-醇、己醇、反-2-辛烯醛、1-辛烯-3-醇、苯甲醛、反,反-非二烯醛和己酸足以区分氧化水平，并作为核桃中的氧化标志物。果仁挥发性物质是储存期间核桃氧化的一种有用测量方法，无需事先提取脂肪。
