Analysis Of The Changes Of Grape Polyphenols In Hutai 8 In Response To Storage Temperature And Their Antioxidant Capacity Based On HPLC-MS~2 Technology

Grape is one of the oldest fruits,whether it is used for consumed directly or processed into products,it is deeply loved by consumers.Grape polyphenols,as a physiologically active substance,play a key role in the nutritional quality of grapes.The type and content of grape polyphenols are affected by storage conditions,which in turn affects the nutritional quality of grapes.The nutritional quality of grapes is particularly important to consumers and sellers.Therefore,this experiment explored the accumulation of polyphenols and changes in antioxidant capacity of Hutai No.8 grapes stored at different temperatures(4? and 25?)for different times(1-9 days)through the following aspects:Firstly,the qualitative characteristics of Hutai No.8 grapes were evaluated.It was found that the qualitative indexes such as hardness and chewiness decreased gradually with the increase of storage time,and the qualitative quality of grapes stored at 4? was more stable in comparison.The results showed that the bioactivity(total phenols,total flavonoids and total flavanols)and antioxidant capacity(DPPH,ABTS)of the grapes showed a general trend of increasing and then decreasing with storage time,reaching a peak on the fifth day of storage.The antioxidant capacity was significantly and positively correlated with the content of total phenols and total flavanols.Secondly,qualitative and semi-quantitative analysis.of monomeric phenolic compounds in grape skins was performed using ultra performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry(UHPLC-ESI-qTOF-MS2)and ultra performance liquid chromatography tandem triple quadrupole mass spectrometry(UHPLC-QQQ-MS 2).16 monomeric phenolic compounds were identified,including two flavanols,four flavonols,four phenolic acids and six astragalloids.The trends over time were slightly different,but in general,the phenolic content of most compounds was lower in low temperature storage(4?)than in room temperature storage(25?).Using the quantitative polyphenol results to fit the OPLS-DA model,the clustering results showed significant clustering characteristics for metabolites from grapes stored at two temperatures or stored at different times,and two temperature-related polyphenol differential metabolites,quercetin-3-O-glucoside and 1-o-vanillin-?-D-glucose,were screened,but the polyphenol differential metabolites related to storage time were not screened.Correlation analysis also revealed a significant correlation between phenolics and antioxidant activity in grape skins.Then,the expression levels of key genes in the polyphenol metabolism pathway were analyzed by RT-qPCR.The phenylalanine metabolism pathway genes and the STS genes controlling the production of key enzymes in the synthesis of astragalus compounds were up-regulated during storage.The genes of flavonol metabolism pathway were upregulated at the early stage of storage and down-regulated at the late stage of storage.Changes of gene expression were almost consistent with the changes of compounds.Finally,an in vitro digestion model was established to determine the bioactivity(total phenols,total flavonoids and total flavanols)and antioxidant capacity(DPPH,ABTS)of grape polyphenols after different digestion stages(oral cavity,stomach and intestine).Results showed that the contents of total phenols,total flavonoids and total flavanols decreased after digestion with different parts,and the decrease was greater after digestion with stomach.However,the antioxidant capacity of grape polyphenols increased after digestion.The results proved that grape polyphenols can still play an antioxidant role after being eaten and digested by humans.In this study,Hutai No.8 grapes were stored at different temperatures(4? and 25?)to determine the accumulation of polyphenols and the changes of antioxidant capacity during storage.The changes of polyphenols were explained at the molecular level by the changes of the expression of key genes in the polyphenols metabolism pathway.Finally,in vitro digestion model was used to evaluate the nutritional value of digested grape polyphenols.This will provide some theoretical significance for the research on the storage and transportation of postharvest grapes,contribute to a better understanding of the changes of polyphenols in postharvest grapes.It also provide guidance for consumers to store and eat grapes.