为探明褪黑素(melatonin,MT)对采后青花菜衰老的调控机理,以鲜切青花菜为试验材料,研究了100 μmol/L MT 处理对鲜切青花菜黄化指数、色差、内源褪黑素含量、总叶绿素含量、呼吸途径、能量水平、抗氧化物酶及其同工酶活性的影响.结果表明,贮藏第6 d时CK0、CK1组青花菜的黄化指数分别为1.93、2.08,而MT处理组青花菜在贮藏第7 d的黄化指数仅为1.71,同时MT处理明显抑制了采后青花菜L*、a*、b*值的上升(P<0.05);随着贮藏时间的延长,青花菜叶绿素含量不断下降,然而至第6 d时,MT组青花菜的叶绿素较CK0、CK1组分别高出18.03%、24.15%.另外,MT处理降低了采后青花菜的总呼吸强度、糖酵解途径、三羧酸循环途径和细胞色素呼吸途径的活性(P<0.05),提高了其交替途径的活性(P<0.05),并维持了其较高的能荷水平(P<0.05);此外,MT 处理降低了采后青花菜组织内O2?-和H2O2含量的积累(P<0.05),这可能与其维持组织较高的超氧化物歧化酶、过氧化氢酶、过氧化物酶及其同工酶活性有关(P<0.05).这些结果表明MT处理可通过调控采后青花菜的呼吸代谢及抗氧化活性而延缓其衰老进程,可为褪黑素应用与青花菜贮藏保鲜提供新的理论支撑.%Broccoli (Brassica oleracea L. var.italica Planch) florets are one of the nutrient-rich vegetables, which contain carbohydrates, protein, carotenoids, dietary fiber, vitamins, antioxidant substances, and anti-carcinogenic compounds. Fresh broccoli is therefore highly popular. Color is an extremely important quality attribute of fresh broccoli. "Yellowing" is the term used to describe the color quality. Under ambient temperature, the florets yellow rapidly accompanied by chlorophyll degradation, and the shelf life of broccoli is only 2-3 d. Therefore, it is important to keep the green color as long as possible for quality maintenance. As a safe and beneficial indoleamine molecule, melatonin exists in different organs of plant, such as roots, stems, leaves, flowers and fruits. Apart from acting as endogenous elicitor and signaling role, melatonin has a direct antioxidant activity for attenuation of biotic and abiotic stress, including salt, drought, cold, and pathogens. The senescence of fruits and vegetables is usually accompanied by increased level of reactive oxygen species. However, whether melatonin regulates the senescence and yellowing of postharvest broccoli remains unknown. In this study, to explore an effective preservation technology for postharvest broccoli, the effects of 100 μmol/L melatonin treatment on the yellowing index, chromatic aberration, endogenous melatonin content, total chlorophyll content, respiratory pathway, energy level, and antioxidant activity of fresh-cut broccoli were investigated based on the results of our preliminary experiments. The results showed that, the yellowing index in no-treated and distill water-treated broccolis were 1.93, 2.08 on the sixth day, respectively. However, the yellowing index of melatonin-treated group was only 1.71 on the seventh day. Meanwhile, melatonin treatment inhibited the increase of the values of L*, a*, and b*. The contents of total chlorophyll in postharvest broccoli decreased with the extent of storage time, while the content of total chlorophyll in melatonin-treated group were 18.03%, 24.15% highter than that in no-treated and distill water-treated groups on the sixth day, respectively. Additionally, at the substrate oxidation level, melatonin treatment reduced the total respiration rate of postharvest broccoli florets by reducing the operating proportion of embden-meyerhof-parnas (EMP), tricarboxyfic acid cycle (TCA) and phosphopentose pathway (PPP). At the level of electron transport chain, melatonin treatment decreased the operating proportion of cytochrome pathway (CP) and increased the operating proportion of alternate pathway (AP) (P<0.05). Meanwhile, melatonin treatment maintained higher contents of adenosine triphosphate (ATP) and adenosine diphosphateadenosine (ADP), and a lower content of adenosine monophosphate (AMP), thereby showing a higher energy status in the melatonin-treated samples during the whole storage period (P<0.05). Furthermore, melatonin treatment ameliorated the accumulation of O2?- and H2O2compared to the control broccolis (P<0.05), which might be associated with the increased activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), and the deduction was supported by an increased activities of SOD, CAT and POD isozymes. Overall, these results suggest that melatonin can delay the senescence process of postharvest broccoli florets through regulating the respiratory metabolism and antioxidant activity, which will provide a new theoretical basis for the application of melatonin and the preservation of broccoli.
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