Study On The Effect Of Elevated Carbon Dioxide On Sugar,acid Accumulation And Phenolic Metabolism In Postharvest Wolfberry

Fresh fruit of Lycium barbarum is rich in nutrients and is favored by consumers,but it has soft flesh and is perishable.In this paper,the fresh wolfberry fruit(Lycium barbarum L.cv.Ningqi No.10)was placed in different carbon dioxide concentrations(0,5%,10%,15%),and stored at 0℃ for 28 days.During storage time,the physiological characteristics and cell wall metabolism of fresh wolfberry fruit were determined,the content of sugar,organic acid,and phenolic compounds in fresh wolfberry fruit were analyzed by targeted metabolomics,the spatial distribution and abundance of differential metabolites were analyzed by spatial metabolomics,and the key enzymes activities and expression level of gene key genes in its metabolic pathways were verified.The main contents and conclusions are as follows:(1)The effects of elevated carbon dioxide on the morphological and microstructural characteristics of fresh wolfberry fruit during storage were studied.The results showed that elevated carbon dioxide inhibited the weight loss and rot,maintained the color and firmness of the fruit,inhibited the increase of cell membrane permeability and malondialdehyde content,and maintained the integrity of cell morphological structure.In addition,elevated carbon dioxide inhibited the decrease of cellulose content,protopectin content,and the increase of soluble pectin content,as well as cell the activity of cell wall degradation enzymes(polygalacturonase,pectin lyase,cellulase,β-glucosidase).Therefore,elevated carbon dioxide plays an important role in delaying fruit senescence and stabilizing cell structure.(2)The effects of elevated carbon dioxide on sugar and organic acid accumulation of wolfberry fresh fruit were studied.The results showed that elevated carbon dioxide delayed the increase of soluble solids content and the decrease of titratable acid.Elevated carbon dioxide promoted the decomposition of sugar(glucose,fructose,maltose,and sucrose)compounds and the accumulation of organic acid(succinic acid,3-methylglutaric acid,linoleic acid,nonadecanoic acid)compounds.On day 21,the content of glucose,fructose,maltose,and sucrose in the 10%CO2 treatment was decreased by 42.66%,41.54%,119.64%,and 119.08%,while the content of succinic acid was increased by 259.72%compared with the control group.Elevated carbon dioxide promoted the increase of acid invertase,neutral invertase,and sucrose synthase activities and the decrease of sucrose phosphate synthase activities.Elevated carbon dioxide up-regulated the gene expression of sucrose catabolism LbAI,LbNI,LbSS and glyoxylate cycle metabolism LbICL,LbMDH,down-regulated the gene expression of sucrose anabolism LbSPS and glyoxylate cycle metabolism LbMS,and activated the sucrose catabolism and glyoxylate metabolism.(3)The effects of elevated carbon dioxide on the phenolic metabolism of wolfberry fresh fruit were studied.The results showed that elevated carbon dioxide inhibited the decrease of total phenols and flavonoids contents during storage,and maintained higher ABTS and DPPH radical scavenging activity.Elevated carbon dioxide promoted the accumulation of 11 kinds of phenolic compounds.On day 21,the content of chlorogenic acid and rutin in the 10%CO2 treatment increased by 181.25%and 27.77%compared with the control group.Elevated carbon dioxide up-regulated the gene expression of phenylpropanoid metabolism LbPAL,LbC4H,Lb4CL,and flavonoid metabolism LbCHS,LbCHI,LbF3H,LbDFR,LbANS,and LbLAR,which further verified that elevated carbon dioxide can maintain the nutritional contents of fresh wolfberry fruit.