Study On Postharvest Quality Deterioration And Control Technology Of Pomegranate

Pomegranate(Punica granatum L.),a berry with attractive appearance and high economic,is very popular with consumers.The pomegranate seeds of which are translucent,sour and sweet in taste,and rich in nutrition.The pomegranate fruit is quite susceptible to the problems such as browning,dehydration,shrinkage and corrosion during storage,which has severely affected its appearance quality and commercial value.In this study,two main pomegranate varieties from Panxi region of Sichuan Province,namely,'Green peel and soft-seed' and 'Tunisia No.1' were selected as the test materials.The physiological characteristic of pomegranate during the storage,quality changes of peel and seed,as well as the preservation technology to control deterioration of pomegranate quality were investigated.In addition,the key factors influencing the deterioration of pomegranate quality during the storage had been determined,the targeted solutions had been proposed as well,and based on that the composite preservation technology to control the quality deterioration had been formed,which had provided a theoretical basis and practical foundation for the storage and preservation of post-harvest pomegranate.The results were shown as follows:1.The quality changes of pomegranate peel during the storage were mainly shrinkage,dark-colored and browning.Furthermore,the total phenols and punicalagin content of pomegranate peel during the storage decreased,and malondialdehyde content and cell membrane permeability increased.The activity of peroxidase and polyphenol oxidase changed obviously.This indicated that the browning of pomegranate peel resulted from a comprehensive action of fruit rotting,weight loss,peel dehydration,tissue and cell aging as well as enzymatic browning.The quality changes of pomegranate seeds during the storage were mainly color deterioration,flavor fading and browning.The sensory quality of pomegranate seeds during the storage was remarkably correlated with its L*value,a*value,total acid content,soluble solid content,decay rate and weight loss rate.2.The changes in pomegranate respiratory physiology,decay and weight loss,quality of peel and seed during the storage under different temperatures had also been studied.It was found that the optimal preservation effect of both pomegranate varieties could be achieved at 6? with relatively slight deterioration of fruit quality during the storage and shelf life.3.The contents of all 16 amino acids in pomegranate seeds presented a declining trend during the storage,but the percentage of each type of amino acid in the total amino acids showed no obvious changes.The type of seed volatile substances was decreased and then increased,and the changes in their relative contents mainly manifested as increasing terpene substances while decreasing aldehydes substances,and theremaining types had relatively low contents,which displayed no unobvious varying pattern.4.Pathogens responsible for rotting of pomegranate during the storage had been identified with the means of morphology and molecular biology,which were Coniella granati,Neofusicoccum parvum,Botrytis cinerea,Botryosphaeria dothidea and Alternaria sp.,respectively.Of them,Coniella granati had the strongest pathogenicity,which could evidently enhance the fruit respiration rate and ethylene release rate,improve the activities of polyphenol oxidase,peroxidase and phenylalanine ammonialyase after it infected pomegranate.As a result,it would lead to significantly reduced the contents of TSS,TA and Vc in the seed,together with severely damaged seed appearance.Neofusicoccum parvum ranked the second place in terms of pathogenicity.Indoor toxicity test results of 5 pathogens using 18 preservatives and 5 plant essential oils showed that,dehydroacetic acid sodium,?-polylysine and ethylp-hydroxybenzoate had relatively good antibacterial effects among the preservatives,while the cinnamon essential oil,thyme essential oil and syzygium essential oil had stronger antibacterial effects among the plant essential oils.5.The different packing modes were used to control the quality deterioration of pomegranate peel.The result revealed that the whole package with 0.01mm PE bage could achieve the optimal effect.The peel browning index of treated pomegranate was notably lower than that of the control group,which contributed to preserving better L*value,firmness and water content of the peel.Moreover,the activities of polyphenol oxidase and peroxidase were inhibited to some extent.Besides,ozone,jasmonic acid methyl ester,3 preservatives and 3 plant essential oils with strong antibacterial effects had been chosen to control the rotting and quality deterioration of pomegranate grain during storage.The results displayed that,5.0 mg/L ozone fumigation,fruit soaking by 250 mg/L deoxidized sodium acetate solution,and 800 ?L/L cinnamon essential oil fumigation,could effectively control the rotting of pomegranate during the storage,so that the seeds could maintain good quality.The selected single preservative methods mentioned above were integrated,and the principal component analysis was used to screen out the optimal preservation technologies for pomegranate during the storage,which were:1)fruit soaking by 250 mg/L deoxidized sodium acetate solution for 5 min;2)5.0 mg/L ozone sealed fumigation for 1 h for once every 7 days;3)whole package with 0.01mm PE bage;and 4)cold storage at 6?.The decay rates of'Green peel and soft-seed' and 'Tunisia No.1' pomegranates treated by this method were 18.89%and 20.00%respectively after 120 days;their weight loss rates were 4.40%and 3.91%respectively;the peel browning indexes were 0.36 and 0.25 respectively;and the fruits had maintained good quality.