This study aimed to investigate the structural features, antioxidant activity, tyrosinase inhibitory effect, and mechanism of proanthocyanidins from leaf and fruit of Leucaena leucocephala. MALDI-TOF-MS, thiolysis coupled with HPLC-ESI-MS, and 13C-NMR confirmed that these proanthocyanidins were complex mixtures of propelargonidins, procyanidins, and prodelphinidins. (Epi)catechin, (epi)gallocatechin, (epi)catechin gallate, and (epi)gallocatechin gallate were the main constitutive units. The findings obtained from enzyme analysis revealed that the proanthocyanidins had inhibitory effects on both monophenolase and diphenolase of tyrosinase. The IC50 values of leaf and fruit proanthocyanidins were 73.5 ± 2.7 and 52.3 ± 3.5 µg/mL for monophenolase activity, and 27.2 ± 1.4 and 16.1 ± 1.1 µg/mL for diphenolase activity, respectively. The inhibition of diphenolase by proanthocyanidins were proved to be reversible and mixed type. In addition, it was also found from various antioxidant methods that the proanthocyanidins in leaf and fruit possessed potent DPPH radical scavenging activity with IC50 values of 103.4 ± 0.8 and 87.8 ± 1.1 µg/mL, ABTS radical scavenging activity with IC50 values of 72.9 ± 0.4 and 65.7 ± 0.9 µg/mL, and ferric reducing antioxidant power with FRAP values of 3.74 ± 0.03 and 4.02 ± 0.15 mmol AAE/g, respectively. The results obtained suggested that the proanthocyanidins from leaf and fruit of L. leucocephala might have the potential to be exploited as natural tyrosinase inhibitors and antioxidants.

中文翻译：

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银合欢叶和果实中原花青素的抗氧化和抑制酪氨酸酶作用及其机制的结构解析与评价

本研究旨在探讨银合欢叶和果实中原花青素的结构特征、抗氧化活性、酪氨酸酶抑制作用及其作用机制。MALDI-TOF-MS、硫解结合 HPLC-ESI-MS 和 13C-NMR 证实这些原花色素是 propelargonidins、原花青素和 prodelphinidins 的复杂混合物。(epi)儿茶素、(epi)没食子儿茶素、(epi)儿茶素没食子酸酯和(epi)没食子儿茶素没食子酸酯是主要的构成单元。酶分析结果表明，原花青素对酪氨酸酶的单酚酶和双酚酶均有抑制作用。叶和果实原花青素的 IC50 值对于单酚酶活性分别为 73.5 ± 2.7 和 52.3 ± 3.5 µg/mL，对于双酚酶活性分别为 27.2 ± 1.4 和 16.1 ± 1.1 µg/mL。原花青素对二酚酶的抑制作用是可逆的和混合型的。此外，从各种抗氧化方法还发现，叶和果实中的原花青素具有较强的DPPH自由基清除活性，IC50值为103.4±0.8和87.8±1.1μg/mL，ABTS自由基清除活性的IC50值为72.9±0.4。和 65.7 ± 0.9 µg/mL，以及铁还原抗氧化能力，FRAP 值分别为 3.74 ± 0.03 和 4.02 ± 0.15 mmol AAE/g。所获得的结果表明，来自L. leucocephala 叶和果实的原花青素可能具有作为天然酪氨酸酶抑制剂和抗氧化剂开发的潜力。各种抗氧化方法还发现，叶和果实中的原花青素具有较强的DPPH自由基清除活性，IC50值为103.4±0.8和87.8±1.1μg/mL，ABTS自由基清除活性的IC50值为72.9±0.4±65.7± 0.9 µg/mL 和铁还原抗氧化能力，FRAP 值分别为 3.74 ± 0.03 和 4.02 ± 0.15 mmol AAE/g。所获得的结果表明，来自L. leucocephala 叶和果实的原花青素可能具有作为天然酪氨酸酶抑制剂和抗氧化剂开发的潜力。各种抗氧化方法还发现，叶和果实中的原花青素具有较强的DPPH自由基清除活性，IC50值为103.4±0.8和87.8±1.1μg/mL，ABTS自由基清除活性的IC50值为72.9±0.4±65.7± 0.9 µg/mL 和铁还原抗氧化能力，FRAP 值分别为 3.74 ± 0.03 和 4.02 ± 0.15 mmol AAE/g。所获得的结果表明，来自L. leucocephala 叶和果实的原花青素可能具有作为天然酪氨酸酶抑制剂和抗氧化剂开发的潜力。分别为 74 ± 0.03 和 4.02 ± 0.15 mmol AAE/g。所获得的结果表明，来自L. leucocephala 叶和果实的原花青素可能具有作为天然酪氨酸酶抑制剂和抗氧化剂开发的潜力。分别为 74 ± 0.03 和 4.02 ± 0.15 mmol AAE/g。所获得的结果表明，来自L. leucocephala 叶和果实的原花青素可能具有作为天然酪氨酸酶抑制剂和抗氧化剂开发的潜力。