Han Miaomiao, Zhao Jinjin, Wu Qingzhi, Mao Xiaoying, Zhang Jian
School of Food Science and Technology, Shihezi University, Shihezi 832003, China.
Foods. 2023 Feb 1;12(3):620. doi: 10.3390/foods12030620.
Walnuts are rich in fat and proteins that become oxidized during the processing and storage conditions of their kernels. In this study, the effect of three packaging materials (e.g., polyethylene sealed packaging, polyamide/polyethylene vacuum packaging, and polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging) were investigated on the oxidation, structural and digestive properties of walnut kernel proteins. Results showed that the amino acid content gradually decreased and carbonyl derivatives and dityrosine were formed during storage. The protein molecule structure became disordered as the α-helix decreased and the random coil increased. The endogenous fluorescence intensity decreased and the maximum fluorescence value was blue-shifted. After 15 days of storage, surface hydrophobicity decreased, while SDS-PAGE and HPLC indicated the formation of large protein aggregates, leading to a reduction in solubility. By simulating gastrointestinal digestion, we found that oxidation adversely affected the digestive properties of walnut protein isolate and protein digestibility was best for polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging. The degree of protein oxidation in walnuts increased during storage, which showed that except for fat oxidation, the effect of protein oxidation on quality should be considered. The results of the study provided new ideas and methods for walnut quality control.
核桃富含脂肪和蛋白质，其果仁在加工和储存过程中会发生氧化。本研究考察了三种包装材料（即聚乙烯密封包装、聚酰胺/聚乙烯真空包装和聚对苯二甲酸乙二酯/铝箔/聚乙烯真空包装）对核桃仁蛋白质氧化、结构及消化特性的影响。结果表明，储存过程中氨基酸含量逐渐降低，同时形成了羰基衍生物和二酪氨酸。随着α-螺旋减少、无规卷曲增加，蛋白质分子结构变得无序。内源荧光强度降低，最大荧光值发生蓝移。储存15天后，表面疏水性降低，而SDS-PAGE和HPLC表明形成了大的蛋白质聚集体，导致溶解度降低。通过模拟胃肠消化发现，氧化对核桃分离蛋白的消化特性产生不利影响，聚对苯二甲酸乙二酯/铝箔/聚乙烯真空包装的蛋白质消化率最佳。储存过程中核桃蛋白质氧化程度增加，这表明除脂肪氧化外，还应考虑蛋白质氧化对品质的影响。该研究结果为核桃品质控制提供了新的思路和方法。
