Effect Of Grape Harvest Maturity On Color Quality And Aging Stability Of Wine

In this study,four kinds of maturity Cabernet Sauvignon grapes,20°Brix（close to maturity）,23°Brix（maturity in Eastern China）,25°Brix（maturity in Western China）and 27°Brix（beyond maturity）,were harvested at the northern of Tianshan Mountain in Xinjiang.The corresponding wines were brewed and aged for 6 months,9 months and 12 months.Grape fruits with different maturity and wines were used as test materials.The basic physical and chemical properties,agronomic traits and the accumulation of color-related substances of grape fruits were compared.The effects of grape maturity on the composition and content of phenolic substances in wines were analyzed.The aging stability of wines during aging and storage was tracked.The regulation of phenolic substances in fruit under different maturity conditions in flavonoid metabolic pathways was expounded by transcriptome.In order to clarify the influence of grape maturity factors on the color quality and aging stability of wine at the molecular level,and lay a theoretical foundation for promoting the scientific control of grape raw material maturity and improving the stability of wine aging in the northern foot of Tianshan Mountains,Xinjiang,and provide a theoretical basis for the selection of grape raw materials for brewing different types of dry red wine.The results showed:（1）During grape maturation,soluble solids content increased with the increase of maturity,grape weight,seed weight and seed number also increased,but total acid content and fruit weight continued to decrease.Anthocyanin content was the highest in moderately overripe grapes;flavonols accounted for 39.97%to44.33%of the total phenolic content in the four maturity grapes;the content of flavan-3-ol in grape fruits with higher maturity was significantly increased.The relative contents of methylanthocyanidins,myricetin and proanthocyanidin B1 were higher in nearly mature grape fruit.The relative contents of anthocyanin,anthocyanin,dimethyl anthocyanin,quercetin,catechin,gallic catechin and epigallocatechin were higher in common harvest maturity grape fruit.The relative contents of methylanthocyanin,kaempferol and procyanidin B2 were higher in moderately overripe grapes.（2）The basic physical and chemical properties of grape wines with different maturity showed differences.At the end of fermentation,the wine produced by moderately overripe grapes had the highest alcohol content of 14.72%vol and the lowest total acid content of 5.45 g·L^-1.The L*value of different maturity wine was higher,and the wine body showed a deeper color state.The a*value of wine samples also reflects the influence of the increase in grape maturity on the red color of wine;the b*value of the wine sample was low but increased with the increase of maturity,which enhanced the yellowing effect of the wine.The increase of C_ab value makes the wine younger.The H_ab value showed that the color of wine was close to the purple-red tone.In the wines with higher grape maturity,the purple tone decreased and the red tone became more obvious.The anthocyanin content in wine reached 3824.86 mg·L^-1 in moderately overripe wine.The content of flavonols in wines with higher maturity was significantly higher than that in other wines,but the total content of flavan-3-ol was relatively low.The relative contents of unacylated anthocyanins,quercetin and catechin in wines brewed by approximately mature grapes were relatively high.Acetylated anthocyanins,quercetin,kaempferol,epigallocatechins and procyanidin B1 are relatively high in wines brewed by grapes with common harvest maturity.The relative contents of malvidin,myricetins,procyanidin B2 and gallocatechin in wine brewed by moderately overripening grape were higher.（3）During wine aging,alcohol content and total acid content decreased,while pH value had no significant difference.In the aging process,a*value decreased,b*value increased,and the color index of wine with low maturity was unstable.Low alcohol content was not suitable for long-term aging,while the color of wine with high maturity was more stable,which could bring better aging potential for wine body.ABTS scavenging rate and DPPH scavenging rate showed a downward trend in the aging stage as a whole,and the stability of scavenging rate was good in grape wines with higher maturity.HRSA clearance rate increased first and then decreased with the increase of maturity;the FRAP reduction ability of wine was improved at the end of alcohol fermentation and aging stage.Correlation analysis showed that anthocyanin,methyl anthocyanin,methyl anthocyanin,dimethyl anthocyanin,acetylated anthocyanin,quercetin,myricetin,gallic catechin and epigallocatechin were significantly correlated with antioxidant capacity of wine,and their changes in wine aging stage should be paid attention to.（4）Transcriptome results showed that the higher the grape maturity,the more specific genes were expressed,and the down-regulated genes increased significantly in the early stage of grape maturity,while the up-regulated genes increased significantly in the later stage.The upstream genes of flavonoid metabolism,Vv PAL,Vv C4H,Vv 4CL and Vv CHS,were highly expressed in grape fruits with higher maturity.The expression levels of Vv F3’H and Vv F3’5’H were increased in grape maturity stage,which promoted the synthesis of phenolic precursors.Vv LODX was highly expressed in grape fruits with higher maturity,increasing the contents of anthocyanin and anthocyanin.Transcription factors Vv MYBA1 and Vv MYBA2positively regulate the expression of Vv UFGT gene.The gene expression of Vv OMT in grape ripening stage was increased,and the content of methylated anthocyanins in grape fruit was increased.Vv FLS was positively regulated by transcription factor Vv MYC1 to increase the contents of quercetin and myricetin.