Abstract：
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, p < 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.
摘要：
核桃是抗氧化剂的天然来源。其抗氧化能力取决于酚类物质的分布和组成。各种形式的关键酚类抗氧化剂(游离，酯化，和结合）在核桃仁（特别是种子皮）中是未知的。本研究使用超高效液相色谱-三重四极杆质谱仪分析了12个核桃品种中的酚类化合物。使用增强回归树分析来鉴定关键抗氧化剂。鞣花酸,没食子酸,儿茶素,阿魏酸,表儿茶素在内核和皮肤中含量丰富。大多数酚酸广泛分布在游离的,酯化，和结合形式在内核中，但更集中在皮肤中的结合酚类。三种形式的总酚水平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,占20%以上，40%,和15%的抗氧化剂，分别。咖啡酸在皮肤中产生高达25%的游离酚和40%的酯化酚。总酚和关键抗氧化剂解释了品种之间抗氧化活性的差异。关键抗氧化剂的识别对于新的核桃工业应用和食品化学中的功能性食品设计至关重要。
