Wu Shutian, Mo Runhong, Wang Ruohui, Li Qingyang, Shen Danyu, Liu Yihua
Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Fuyang 311400, China.
Shanghai Jing'an District Environmental Monitoring Station, Shanghai 200072, China.
Foods. 2023 Feb 15;12(4):825. doi: 10.3390/foods12040825.
Walnut is a natural source of antioxidants. Its antioxidant capacity is determined by the distribution and composition of phenolics. The key phenolic antioxidants in various forms (free, esterified, and bound) in walnut kernel (particularly seed skin) are unknown. The phenolic compounds in twelve walnut cultivars were analyzed using ultra-performance liquid chromatography coupled with a triple quadrupole mass spectrometer in this study. A boosted regression tree analysis was used to identify the key antioxidants. Ellagic acid, gallic acid, catechin, ferulic acid, and epicatechin were abundant in the kernel and skin. The majority of phenolic acids were widely distributed in the free, esterified, and bound forms in the kernel but more concentrated in bound phenolics in the skin. The total phenolic levels of the three forms were positively correlated with antioxidant activities (R = 0.76-0.94, < 0.05). Ellagic acid was the most important antioxidant in the kernel, accounting for more than 20%, 40%, and 15% of antioxidants, respectively. Caffeic acid was responsible for up to 25% of free phenolics and 40% of esterified phenolics in the skin. The differences in the antioxidant activity between the cultivars were explained by the total phenolics and key antioxidants. The identification of key antioxidants is critical for new walnut industrial applications and functional food design in food chemistry.
核桃是抗氧化剂的天然来源。其抗氧化能力由酚类物质的分布和组成决定。核桃仁（尤其是种皮）中各种形式（游离、酯化和结合）的关键酚类抗氧化剂尚不清楚。本研究采用超高效液相色谱-三重四极杆质谱联用技术分析了12个核桃品种中的酚类化合物。利用增强回归树分析来确定关键抗氧化剂。核仁和种皮中富含鞣花酸、没食子酸、儿茶素、阿魏酸和表儿茶素。大多数酚酸在果仁中以游离、酯化和结合形式广泛分布，但在种皮中更集中于结合酚类物质。三种形式的总酚含量与抗氧化活性呈正相关（R = 0.76 - 0.94，P < 0.05）。鞣花酸是果仁中最重要的抗氧化剂，分别占抗氧化剂的20%以上、40%和15%。咖啡酸在种皮中分别占游离酚类的25%和酯化酚类的40%。品种间抗氧化活性的差异可由总酚和关键抗氧化剂来解释。关键抗氧化剂的鉴定对于核桃在食品化学中的新工业应用和功能性食品设计至关重要。
