Study On The Regulation Mechanism Of Melatonin Treatment On Postharvest Senescence Of Fresh-cut Broccoli

Broccoli?Brassica oleracea L.var.italica Planch.?has rich nutrient and medical value which known as the"crown of vegetables".However,deteriorates of postharvest broccoli are very quickly at normal temperature,and easy to flowering and yellowing.The fresh-cut broccoli accelerated its aging process due to mechanical damage,therefore,it is necessary to study the storage and preservation technology of fresh-cut broccoli.In this experiment,fresh-cut broccoli?You Xiu?was used as test material and treated with 100?mol/L melatonin?MT?to investigate the effect of MT on the fresh-keeping of broccoli.And through the influence of MT on the active ingredients,antioxidant capacity,respiratory pathways,chlorophyll metabolism,ethylene biosynthesis of broccoli,and other aspects to further explore the regulation mechanisms of MT on delaying senescence of broccoli.The resultes were as follows:?1?We exporled the effects of 100?mol/L MT on the quality and active ingredients of fresh-cut broccoli.The results showed that under the conditions of?15±1??and 85%⁹0%relative humidity,on the 6th day after storage,the Vc contents of broccoli in the CK0 and CK1 groups were 20.48mg/100g and 22.69mg/100g,respectively,while the Vc content in the MT group was 32.39mg/100g.At the same time,MT treatment maintained higher total phenols,flavonoids and anthocyanins of fresh-cut broccoli.On the 6th day of storage,the contents of glucosinolates of broccoli in CK0,CK1,and MT groups were reduced by 49.95%,57.28%,and 34.55%compared with 0d,respectively.In addition,MT treatment inhibited the accumulation of malondialdehyde?MDA?in fresh-cut broccoli.And also improved the antioxidant capacity of broccoli.?2?We researched the effects of 100?mol/L MT on the respiratory metabolism and antioxidant activity of fresh-cut broccoli.The results demonstrated,at the 6th day of storage,the yellowing index of broccoli in the CK0 and CK1 groups was 1.93 and 2.08,respectively,whereas the yellowing index of broccoli in the MT-treated group was only 1.71 at the 7th day of storage.Simultaneously,MT treatment inhibited the values of L*,a*and b*of broccoli.MT treatment slowed down the total respiration rate of fresh-cut broccoli by reducing the operating proportion of breathing pathways.At the 6th day of storage,the total respiration rate of broccoli in the MT treatment group was decreased by 17.73%and 24.14%compared with the CK0 and CK1 groups,respectively.Furthermore,MT treatment maintained higher contents of adenosine triphosphate?ATP?,adenosine diphosphateadenosine?ADP?and energy level in broccoli florets,MT ameliorated the accumulation of O₂^·-and H₂O₂,which might be associated with the increased activities of antioxidant enzyme.?3?The effects of 100?mol/L MT on the chlorophyll metabolism of fresh-cut broccoli was studied.The results revealed,at the 6th day after storage,the contents of chlorophyll a,chlorophyll b and total chlorophyll of broccoli in CK0 group were 2.99mg/g,0.98mg/g and0.23mg/g,respectively,the contents of chlorophyll a,chlorophyll b and total chlorophyll of broccoli in CK1 group were 2.96mg/g,0.94mg/g,and 0.2mg/g,respectively,while the contents of chlorophyll a,chlorophyll b,and total chlorophyll in the MT group were 3.91mg/g,1.24mg/g,and 0.29mg/g,respectively.At the same time,MT treatment inhibited the activities of chlorophyllase?Chlase?,Mg-dechelatase?MD?and pheophytinase?PPH?.In addition,MT treatment maintained the content of chlorophyll derivatives in fresh-cut broccoli and inhibited the expression of chlorophyll degradation-related genes to varying degrees.?4?We studied the mechanism of regulation of ethylene biosynthesis in fresh-cut broccoli by 100?mol/L MT.The results showed that MT treatment through reduced the content of1-aminocyclopropane-1-carboxylic acid?ACC?,inhibited the activities of the ACC synthase?ACS?and ACC oxidase?ACO?,and restrained the gene expressions of the ACC synthase?BoACS1,BoACS2,BoACS3?and ACC oxidase?BoACO1,BoACO2,BoACO3?in broccoli florets to reduced the amount of ethylene produced during storage in order to delay the aging of postharvest broccoli.Therefore,it can be concluded that MT treatment delays the senescence of broccoli is related to the regulation of ethylene.