采后褪黑素处理对鲜切花椰菜保鲜品质及货架期的影响

为研究采后外源性褪黑素处理对鲜切花椰菜货架期间品质及生理的影响,试验以"雪白"花椰菜为材料,拟从中筛选出有效的使用浓度,进而从生理、细胞和基因表达水平解析褪黑素对鲜切花椰菜保鲜品质的调节作用,以期为探索鲜切花椰菜保鲜和衰老调控的有效途径提供科学依据。采用0.05、0.10、0.50 mmol/L褪黑素溶液浸泡鲜切花椰菜样本15 min,分析货架期间（0、4、8、12、16 d）样本的失重率、硬度、1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl, DPPH）值、总酚含量、抗坏血酸含量、色泽、总硫代葡萄糖苷含量、内源性褪黑素含量、多聚半乳糖醛酸酶（polygalacturonase, PG）和脂氧合酶（lipoxygenases, LOX）活性及基因表达水平、细胞超微结构的变化。结果表明：0.10 mmol/L褪黑素处理明显延缓（P<0.05）了失重率、硬度、色泽和总硫代葡萄糖苷含量的下降,提升（P<0.05）了样本中内源性褪黑素的含量。同时,0.10 mmol/L褪黑素处理最有利于提高总酚含量和抗氧化能力,延缓抗坏血酸的降低。此外,0.10 mmol/L可抑制细胞结构的损伤,降低PG和LOX的基因表达,延缓PG和LOX的活性。由此可知,对鲜切花椰菜进行外源褪黑素处理可能是延长其采后寿命和提高品质的有效技术。

Influences of post-harvest melatonin treatment on preservation quality and shelf life of fresh-cut cauliflower

Fresh-cut cauliflower has special economic significance in post-harvest management, as a vegetable with a high perishable rate. Among them, melatonin is a kind of indoleamine that plays an important role against abiotic stress. This study aims to evaluate the effect of 0.05, 0.10, and 0.50 mmol/L of melatonin on the preservation quality of nutritionals in the fresh-cut cauliflower during 16-day storage at 4°C. Six samples of each replicate were randomly taken at 0, 4, 8, 12, and 16 days after treatment to measure weight loss, firmness, color, polygalacturonase (PG), and lipoxygenase (LOX) activities, and PG and LOX expression. The rest of the fruits were immediately frozen in liquid nitrogen and stored at ?80 °C before determining the endogenous melatonin levels and DPPH radical scavenging activity, total phenolic, ascorbic acid, and total glucosinolates contents. The results showed that the nutritional quality was clearly delayed (P<0.05) by the 0.10 mmol/L melatonin treatment, as disclosed by the weight loss, firmness, color, total glucosinolates content, and endogenous melatonin content of fresh-cut cauliflower samples. Furthermore, 0.10 mmol/L melatonin treatment was optimal for the enhancement (P<0.05) of total phenolic content and antioxidant capacity, indicating that it delayed (P<0.05) the reduction in ascorbic acid. Moreover, 0.10 mmol/L melatonin treatment enhanced (P<0.05) PG expression, where decreased first and then increased (P<0.05) LOX gene expression during storage, and delayed (P<0.05) the activities of PG and LOX. After storage for 16 days, the changes of cellular structure in the 0.10 mmol/L treatment group and control group were observed under a Transmission Electron Microscope (TEM). The results showed the 0.10 mmol/L treatment sample cells presented obvious slight plasmolysis after storage for 16 days, where a small amount of autophagy was observed, while the slight plasmodesmata were also found between the cells. However, some variations of cells were also observed as follows: the mitochondria of cells in the ultrastructure of cauliflower florets in the absence of melatonin treatment (control) were moderately swollen, the endoplasmic reticulum was moderately expanded, autophagy appeared, and the cytoplasm and cell wall were separated. Consequently, the finding demonstrated that the melatonin treatment may be expected to serve as a useful technique to extend the postharvest life and improve quality in fresh-cut cauliflower.