| Broccoli has rich nutrient and medical value which is known as "Vegetable crown".However,broccoli deteriorates very quickly after harvest at ambient due to the loss of green color and the consequent yellowing of florets,let alone the fresh-cut one,which severely limits the industrial and commercial development of fresh-cut produces.This study was focused on fresh cut broccoli(YouXiu)immersed with water(as the control)and with 30 mg/L 6-BA,stored at(15±1)? and 90%?95%relative humidity to investigate the effect of 6-BA on nutritionalquality,as well as the antioxidant capacity and the activity of antioxidant enzymes of fresh cut broccoli.Based on this,we further to study the effect of 6-BA on the ethylene metabolism,respiratory pathways and energy metabolism of fresh cut broccoli to provide a reference for the application of 6-BA in fresh cut broccoli.The results were as follows:(1)We researched the effects of 30 mg/L 6-BA on storage quality of fresh cut broccoli.Our study results demonstrated that fresh cut broccoli was highly resistant to storage,yellowing in the second day,darking in the fourth day,then gradually losing nutritional value and moldy and rotten.6-BA treatment improved the storage quality,significantly slowed the decline in sensory quality and the change of color,inhibited the chlorophyll degradation and kept the commodity value in the seventh day of fresh cut broccoli.Meanwhile,6-BA treatment effectively reduced weight loss,slowed the degradation of soluble sugar,soluble protein,titratable acid,and retarded lignifications of fresh cut broccoli.Additionally,6-BA treatment inhibited the accumulation of nitrite.(2)We explored the effects of 30 mg/L 6-BA on the content of antioxidants,antioxidant capacity and the activity of antioxidant enzymes of fresh cut broccoli.The results of this analysis revealed that treatment with 30 mg/L 6-BA effectively retained higher total phenol and flavonoids content,delayed the decreasing of Vc,and glucosinolates content,reduced the accumulation of malonaldehyde(MDA)content and hydrogen peroxide(H2O2)content.Simultaneously,6-BA protected the activity of ascorbate peroxidase(APX)and the integrity of the cell memlbrane,improved the activity of superoxidedismutase(SOD)and catalase(CAT),passivated the activity of peroxidase(POD)and polyphenol oxidase(PPO).Therefore,6-BA enhanced free radical scavenging capacity of super oxide anion radical,hydroxyl radical,1,1-diphenyl-2-picryl-hydrazyl(DPPH)radical and reducing activity.These results provided the theoretical basis for a novel technique for the preservation of fresh cut broccoli,wich is conducive to the development of fresh cut broccoli industry.(3)To check the possible regulatory mechanism of 6-BA in regulating the senescence of broccoli,the effects of 30 mg/L 6-BA on the endogenous 6-BA content,total bacteria account,ethylene production,the expression of senescence-related genes,activity of the ethylene-forming enzyme and their genetic expressions of broccoli were investigated.The results showed that 6-BA treatment could significantly inhibite the increase of total bacteria account in broccoli.The endogenous 6-BA content of broccoli(control)continuously decreased with the extent of storage time,while exogenous 6-BA treatment maintained the higher endogenous 6-BA content at the later stage of storage.The endogenous 6-BA content both in the control and 6-BA treatment were obviously decreased after cooking.Additionally,6-BA treatment down-regulated the expressions of Broccoli chlorophyllase 2(BoCLH2),Broccoli cysteine protease 5(BoCP5),Proline rich protein(BoLSC810),relieved the decline of Broccoli chlorophyll a/b binding protein 1(BoCABl)expression.Moreover,6-BA treatment significantly suppressed the ethylene production of broccoli,which might be associated with the decreased activity of ethylene synthase(ACS)and down-regulated expression of BoACS1,BoACS2.These results suggested that exogenous 6-BA maintained the higher endogenous 6-BA level at the later period of storage,thereby inhibited the ethylene production,and finally slowed down the senescence of broccoli.(4)To clear the effect of 6-benzylaminopurine(6-BA)treatment on the respiratory pathway and energy level in fresh cut broccoli,the effect of 6-BA treatment on total respiration intensity,the change of respiratory pathways including krebs cycle pathway(TCA)phosphopentose pathway(PPP),cytochrome pathway(CP),and alternate pathway(AP),the accumulation of O2-·,levels of adenosine monophosphate(AMP),adenosine diphosphate(ADP)and adenosine triphosphate(ATP)and energy status in postharvest broccoli florets were investigated.The results showed that the 6-BA treatment delayed the deterioration of exterior quality and significantly decreased the total respiration intensity,the activities of CP and PPP but increased the expression of the AP.In addition,in late storage(6?10 d),6-BA treatment reduced the proportion of the activities of TCA,promoted the accumulation of ATP and maintained a higher level of energy charge in fresh cut broccoli,and thereby,inhibited the accumulation of O2-· in fresh cut broccoli.Thus,the inhibition of 6-BA on the senescence of fresh cut broccoli might be associated with the regulation of respiratory pathways and the maintenance of energy charge.In conclusion,6-BA treatment improved the storage quality of the fresh cut broccoli,this might be related to 6-BA which could delay the degradation of antioxidant compounds,improve the ability of antioxidant and the activity of antioxidant enzymes of fresh cut broccoli tissues,and which might also be associated with the inhibition of ethylene production,the regulation of respiratory pathways and the maintenance of energy charge by 6-BA. |
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