College of Food Science and Technology , Hainan University , Haikou 570228 , PR China.
Horticultural Sciences Department, IFAS , University of Florida , PO Box 110690, Gainesville , Florida 32611-0690 , United States.
J Agric Food Chem. 2018 Jul 18;66(28):7475-7484. doi: 10.1021/acs.jafc.8b01922. Epub 2018 Jul 10.
Melatonin acts as a crucial signaling and antioxidant molecule with multiple physiological functions in organisms. To explore effects of exogenous melatonin on postharvest browning and its possible mechanisms in litchi fruit, 'Ziniangxi' litchi fruits were treated with an aqueous solution of melatonin at 0.4 mM and then stored at 25 °C for 8 days. The results revealed that melatonin strongly suppressed pericarp browning and delayed discoloration during storage. Melatonin treatment reduced relative membrane-leakage rate and inhibited the generation of superoxide radicals (O), hydrogen peroxide (HO), and malondialdehyde (MDA). Melatonin treatment markedly promoted the accumulation of endogenous melatonin; delayed loss of total phenolics, flavonoids, and anthocyanins; and enhanced the activities of antioxidant enzymes, including superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2). By contrast, the activities of browning-related enzymes including polyphenoloxidase (PPO, EC 1.10.3.1) and peroxidase (POD, EC 1.11.1.7) were reduced. In addition, melatonin treatment up-regulated the expression of four genes encoding enzymes for repair of oxidized proteins, including LcMsrA1, LcMsrA2, LcMsrB1, and LcMsB2. These findings indicate that the delay of pericarp browning and senescence by melatonin in harvested litchi fruit could be attributed to the maintenance of redox homeostasis by the improvement of the antioxidant capacity and modulation of the repair of oxidatively damaged proteins.
褪黑素作为一种重要的信号和抗氧化分子，在生物体中具有多种生理功能。为了探讨外源褪黑素对荔枝果实采后褐变的影响及其可能的机制，本研究以‘孜娘希’荔枝果实为试材，用 0.4 mM 褪黑素水溶液处理，然后在 25℃下贮藏 8 天。结果表明，褪黑素强烈抑制果皮褐变，延缓贮藏过程中的变色。褪黑素处理降低了相对膜渗透率，抑制了超氧自由基（O）、过氧化氢（HO）和丙二醛（MDA）的生成。褪黑素处理显著促进了内源性褪黑素的积累；延缓了总酚、类黄酮和花色苷的损失；增强了抗氧化酶的活性，包括超氧化物歧化酶（SOD，EC 1.15.1.1）、过氧化氢酶（CAT，EC 1.11.1.6）、抗坏血酸过氧化物酶（APX，EC 1.11.1.11）和谷胱甘肽还原酶（GR，EC 1.6.4.2）。相比之下，褐变相关酶如多酚氧化酶（PPO，EC 1.10.3.1）和过氧化物酶（POD，EC 1.11.1.7）的活性降低。此外，褪黑素处理上调了 4 个编码氧化蛋白修复酶的基因的表达，包括 LcMsrA1、LcMsrA2、LcMsrB1 和 LcMsB2。这些发现表明，褪黑素延迟荔枝果皮褐变和衰老可能归因于通过提高抗氧化能力和调节氧化损伤蛋白的修复来维持氧化还原平衡。
