Effect Of Ultrasound On Pomegranate Fruit Quality And Analyzing Browning Mechanism Based On Metabolome

Pomegranate fruit is juicy and delicious,and is widely popular among consumers and fruit merchants due to rich nutritional elements and high healthy and economic values,which promotes the development of pomegranate industry.However,pomegranate fruit often suffer from quality deterioration such as fruit browning,seed shriveling,softening and rotting due to water loss,high respiratory intensity,cell membrane structure damage,and microbial infection during postharvest storage.Quality deterioration of fruit not only shortens the storage life of pomegranate fruit after harvesting,but also greatly reduces the nutritional value and commercial value,which seriously affects the development of pomegranate industry chain.Therefore,it is important to explore the mechanism of postharvest quality deterioration(such as browning,rot)and preservation technology for the pomegranate industry development.Ultrasound technology,as a physical stimulus,uses mechanical short waves beyond the human hearing to treat fruits and vegetables.Ultrasound technology does not use any chemical additives,so it is green and safe.Ultrasound treatment for postharvest horticultural products can maintain the higher quality and nutritional value.At present,the application of ultrasound technology in postharvest pomegranate fruit has not been extensively studied.To explore the effect of ultrasound treatment on the quality of pomegranate fruit during shelf life,ultrasound technology was used to treat ‘Tunisian soft seed’ pomegranate for 10 minutes and 30 minutes,respectively,then simulated the shelf life to store for 30 days.And fruit quality traits and related physiological indices were analyzed to provide theoretical and technical support for the application of ultrasound technology in postharvest storage of pomegranate.Browning has a high incidence during the storage of pomegranate,and secondary metabolites(especially phenolics)are involved in browning,which seriously limits the development of pomegranate industry.In this study,the comprehensive comparative analysis was explored in the healthy and browning pomegranate arils based on firstly widely targeted secondary metabolomics combined with relevant physiological and biochemical indices.Therefore,the present study will contribute to analyze the browning mechanism of pomegranate arils.The results of the analysis showed that:(1)Compared with the control group,ultrasound treatment can prolong the shelf life of pomegranate fruits,maintain the higher fruit quality,and still have higher sensory evaluation scores after 30 days of storage.The treated pomegranate fruits had better appearance quality(color,browning rate,etc.),higher nutritional quality(ascorbic acid,anthocyanin content,etc.)and antioxidant capacity(superoxide dismutase and catalase activity),compared to the control group.(2)Ultrasound treatment(especially for 30 min)significantly reduced the browning rate(always below 5%),weight loss(9.54% lower than the CK)and peroxidase(POD)activity of pomegranate fruits during storage,and improved ascorbic acid(As A)content and the antioxidant activity of catalase(CAT).In addition,the total number of bacteria,mold and yeast colonies in pomegranate fruit in the treatment group were significantly inhibited.Combined with WGCNA analysis,ultrasound treatment improved pomegranate fruit color and antioxidant capacity by reducing oxidase activity,so the reduction of oxidase activity in pomegranate fruit treated by ultrasound was the main reason for the relatively higher fruit quality.(3)Based on metabolomic data analysis,a total of 399 secondary metabolites were identified in pomegranate arils.And 89 significantly different metabolites were identified,including 75 up-regulated and 14 down-regulated in browning arils.According to the KEGG enrichment analysis,flavonoid,flavone and flavonol biosynthesis were mainly involved in the aril browning,especially,phenylpropanoid biosynthesis.(4)Further analysis of phenylpropanoid biosynthesis revealed that p-coumaric acid was a key metabolite in aril browning,which can inhibit melanin production and is a precursor for the biosynthesis of caffeic acid,ferulic acid,butin,and phloretin.Among the seven anthocyanin derivatives,only cyanidin-3-O-arabinoside was upaccumulated in browning arils,indicating its greater effect on pomegranate aril browning.In conclusion,ultrasound treatment can better maintain the postharvest pomegranate fruit quality and improve the commercial value,which will be helpful to explore the application of ultrasound technology in other fruits and vegetables.The browning mechanism based on secondary metabolome showed that pomegranate aril browning mainly includes enzymatic oxidation reaction of PPO,water loss during storage and hydrolysis reaction,which provides the theoretical basis for further analysis of pomegranate fruit browning.