Mulberry (Morus alba L.) leaves are widely used as herbal tea to prevent heat stroke. Potential chemical markers of the antioxidant properties and its correlation with harvesting times and leaf location were explored in this study. A 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay guided isolation of mulberry leaves extract provided five phenolic compounds: 5-O-caffeoylquinic acid (1), 4-O-caffeoylquinic acid (2), gastrodin (3), isoquercetin (4) and rutin (5). The 50% radical-scavenging concentrations (SC50) of these compounds were 32.76 ± 0.27, 11.41 ± 0.48, 404.30 ± 4.92, 10.63 ± 0.96, and 10.57 ± 0.61 μg/mL, respectively. Chromatographic fingerprinting allowed content analysis of 1-5 in samples over a 12-month period. Compounds 1-5 were abundance in apical leaves (0-10 cm) in January and February at temperatures < 20 °C. Contents of 2 and 5 were highest in these months and were strongly correlated to the antioxidant property. Therefore, we suggested that the mulberry leaves harvested during January and February have high yield of 4-O-caffeoylquinic acid and this compound can be used as antioxidative marker in mulberry leaves.

中文翻译：

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4- O-Caffeoylquinic acid 作为桑叶中富含酚类化合物的抗氧化标志物

桑叶 (Morus alba L.) 的叶子被广泛用作凉茶来预防中暑。本研究探讨了抗氧化特性的潜在化学标记及其与收获时间和叶片位置的相关性。2,2-二苯基-1-苦基肼 (DPPH) 自由基清除试验指导桑叶提取物的分离提供了五种酚类化合物：5-O-咖啡酰奎尼酸 (1)、4-O-咖啡酰奎尼酸 (2)、天麻素 ( 3)、异槲皮素(4)和芦丁(5)。这些化合物的 50% 自由基清除浓度 (SC50) 分别为 32.76 ± 0.27、11.41 ± 0.48、404.30 ± 4.92、10.63 ± 0.96 和 10.57 ± 0.61 μg/mL。色谱指纹分析允许在 12 个月内对样品中的 1-5 进行含量分析。在温度 < 20 °C 的 1 月和 2 月，化合物 1-5 在顶端叶 (0-10 cm) 中含量丰富。2 和 5 的含量在这几个月中最高，并且与抗氧化性能密切相关。因此，我们建议1月和2月采收的桑叶中4-O-咖啡酰奎宁酸产量较高，该化合物可作为桑叶中的抗氧化标志物。