核桃仁发育过程中不同形态酚及其抗氧化活性的动态变化

阐明发育期核桃仁中3种不同形态酚（游离、酯化和结合）及其单体酚组成的变化，探究酚类成分与抗氧化能力的关系，为深入了解核桃功能性成分形成规律和深化功能性产品开发提供参考。以核桃品种‘寒丰’为对象，运用UPLC-MS/MS测定3种形态酚组成，分光光度计法测定核桃的羟自由基清除能力，皮尔逊相关分析用于研究酚类物质与羟自由基清除能力的相关性关系。在核桃仁发育过程中，酚形态中以游离态为主且占比大于58%；3种形态总酚含量最高值均出现在采前63 d，分别为10.47 mg/g（游离态）、2.76 mg/g（酯化态）、1.28 mg/g（结合态）；鞣花酸、咖啡酸、绿原酸等单体酚的3种形态含量随着核桃仁发育显著降低58.03%-88.83%；单体酚含量与抗氧化活性呈现显著相关性，相关系数为0.63-0.97。核桃仁3种形态总酚含量和抗氧化活性最大值均出现在未成熟早期，游离态是核桃仁中提供抗氧化活性的酚类物质主要形态，并且核桃仁发育过程中单体酚的抗氧化能力与成熟度、酚形态有关。这些发现将对核桃的适时采摘和营养管理以及核桃仁深度开发利用、产业提质增效等提供重要的基础数据和理论参考。

Dynamic changes of different forms of phenols and their antioxidant activities during ripening of walnut kernels

To investigate the relationship between phenolic components and antioxidant capacity, as well as the changes in the composition of three different phenolic forms (free, esterified, and bound) and their monomeric phenols in walnut kernels during development, in order to provide a reference for an in-depth understanding of the formation of functional components in walnuts and to deepen the development of functional products. The three forms of phenolics of the walnut variety ''Hanfeng'' were determined by UPLC-MS/MS, the hydroxyl radical scavenging capacity of walnuts was determined by spectrophotometry, and Pearson correlation analysis was used to investigate the correlation between phenolics and hydroxyl radical scavenging capacity. The free form was the dominant phenolic form during the development of walnut kernels, accounting for more than 58% of the total phenolic content; the highest values of the three forms were found 63 days before harvest, at 10.47 mg/g (free), 2.76 mg/g (esterified), and 1.28 mg/g (bound), respectively; the content of the three forms of monomeric phenols, such as ellagic acid, caffeic acid, and chlorogenic acid, decreased significantly by 58.03% - 88.83%. The monomeric phenolic content showed a significant correlation with the antioxidant activity with a correlation coefficient of 0.63-0.97. The maximum values of total phenolic content and antioxidant activity were found in the early immature stage of all three forms of walnut kernels. The free form was the primary form of phenolics providing antioxidant activity in walnut kernels, and the antioxidant activity of monomeric phenols during walnut kernel development was related to maturity and phenolic form. These findings will provide critical basic data and theoretical references for walnut harvesting and nutritional management, as well as in-depth exploitation of walnut kernels and improvement of industrial quality and efficiency.