褪黑素延缓去壳黄甜笋木质化和褐变作用

周成敏; 陈凯鹏; 黄文仕; 郑剑

doi:10.13386/j.issn1002-0306.2023020305

褪黑素延缓去壳黄甜笋木质化和褐变作用

Effects of Melatonin Treatment on Lignification and Browning in Bamboo Shoots (Acidosasa edulis) Without Sheaths During Cold Storage

摘要

摘要: 为了研究外源褪黑素延缓冷藏去壳黄甜竹笋木质化和褐变的效果，将无机械伤、无病害且外观和尺寸比较均匀接近的黄甜竹笋剥壳、清洗，于150 μL/L次氯酸钠溶液中杀菌5 min，清洗后于空气中晾干。再于0.2 mmol/L褪黑素溶液和清水（对照）（均含有0.05%吐温-80和3 mL无水乙醇）中22 ℃下浸泡30 min，室温下空气中自然晾干约60 min，而后于（6±1）℃和RH 75%~80%下贮藏15 d，定期取样测定其品质指标以及与木质化、褐变、抗氧化相关酶的活性和基因表达量。结果表明，褪黑素处理显著地（P<0.05）下调了苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）和肉桂醇脱氢酶（CAD）基因表达量及活性，从而抑制了笋肉组织的木质化进程；同时，褪黑素处理一方面显著地（P<0.05）提高去壳黄甜笋中超氧化物歧化酶（SOD）、过氧化氢酶（CAT）活性并上调了对应基因表达量，以降低过氧化氢（H₂O₂）含量和超氧阴离子自由基（O₂⁻·）的产生速率，从而延缓了相对电导率上升及丙二醛（MDA）的累积；另一方面，褪黑素降低了多酚氧化酶（PPO）活性并下调对应基因表达量，最终抑制了竹笋切面褐变。综上，外源褪黑素处理能够有效抑制冷藏去壳黄甜竹笋的褐变和木质化。

Abstract: The effects of melatonin treatment on inhibiting lignification and browning, including firmness, lignin content, enzyme activities, and the expression level of genes encoding corresponding enzymes in bamboo (Acidosasa edulis) shoots without sheaths during cold storage were investigated. Bamboo shoots without physical injuries or infections and similar in shape and size were removed from their sheaths and cleaned with tap water and then disinfected with 150 μL/L sodium hypochlorite for 5 min, rinsed with tap water, and air-dried. The bamboo shoots were soaked in 0.2 mmol/L melatonin solution and water (control) (both containing 0.05% Tween-80 and 3 mL anhydrous ethanol) at 22 ℃ for 30 minutes, air-dried at room temperature for approximately 60 min and subsequently stored at 6±1 °C accompanied by 75%~80% RH for 15 days. Quality parameters and activities of key enzymes and gene expression involved in lignification and browning of bamboo shoots were periodically determined during cold storage to investigate the related mechanism. The results showed that melatonin treatment significantly (P<0.05) decreased the activities of phenylalanine ammonia lyase (PAL), peroxidase (POD) and cinnamyl alcohol dehydrogenase (CAD), and the expression of these lignin synthesis-related enzymes, which contributed to retarding lignification process in bamboo shoots. Meanwhile, melatonin treatment decreased hydrogen peroxide (H₂O₂) content and the production rate of superoxide anion radical (O₂⁻·), delayed the increase of MDA content and relative leakage rate by significantly (P<0.05) increasing the activities of superoxide dismutase (SOD), catalase (CAT) and the expression of their encoding genes. On the other hand, melatonin treatment reduced the activities of polyphenol oxidase (PPO) and the expression of the encoding genes in bamboo shoots, consequently delaying the enzymatic browning of bamboo shoots. Thus, exogenous melatonin treatment could effectively inhibit browning and lignification of cold shelled yellow sweet bamboo shoots.