Effects Of Grass And Film Cover On Aroma Quality Of ‘Cabernet Sauvignon' Grape And Wine

In this experiment,cabernet sauvignon,a wine grape from Helan mountain region of Ningxia,was treated with grass(purslane)and film(shading net)respectively in the vineyard,the clear cultivated in the row was control.The influence of this treatment on vineyard microclimate,vine growth and development were monitored in the growing season of the plant.At the same time,we compared the difference of aroma in the grape(at the harvest stage)and the wine(at the end alcohol fermentation and malolactic fermentation)by GC-MS to investage the effects of grass and film on grape and wine quality.The results showed that the treatment of grass and film both had effects on the microclimate,vine growth and development,aroma content of fruit and wine in vineyard.1.The influence of grass and film cover on vineyard microclimateGrass and film conducted in vineyard can adjust the microclimate between berry zone and roots zone.In the hot season of grape growth,the daily average temperature of growing grass and covering treatment groups decreased by 0.5-2°C and 0.3-1°C respectively,and the relative humidity of berry air increased by 5-7% and 2-5%,and the reflected radiation on the ground decreased by 45-60% and 10-20%.The soil water content of 40 cm below the ground surface decreased 20-50 % effected by grass as the competition between grass-growing treatment and plants.However,increased 50-80% by film.2.The effect of grass and film cover on the growth and development of vineBecause microenvironment of the vine was regulated by grass and film cover,which further affected the growth and development of grapes and changes the phenological phase of cabernet sauvignon.In our study,the coversion of berry was changed,it was delayed 3-4 days by grass cover,and the coversion of berry effected by film were delayed 5-10 days.At the same time,the soluble solid content of grape was increased and the total acid were decreased.However,there was no impacted in yield.For grass cover,it can effectively controlled the tree vigor and balanced the reproductive growth and nutritional growth.3.The effects of grass and film cover on aroma compounds in grapes during harvestThe different treatment changed the carbon distribution flow direction in the three major aroma compounds synthesis paths of' cabernet sauvignon',and improved the aroma compounds content of the grape.The total content of free and bound compounds in fatty acid metabolism pathway increased under grass and film cover.The contents of free linear fatty aldehyde,linear fatty acid and linear fatty ester in grape were all increased under the treatment of grass and film cover.The content of bound straight-chain fatty alcohol,straight-chain fatty acid and straight-chain fatty ester in grape of the film treatment group increased.The content of bound linear fatty aldehyde and linear fatty ester in grass treatment group increased,while the content of linear fatty alcohol and linear fatty acid showed different performance in different years.In the amino acid metabolism pathway,grass and film cover cultivation both reduced the free volatile aromatic compounds content and increased the bound volatile aromatic compounds content.There are a different results by years of grass cover on branched-chain aliphatic compounds,while the content of bound branched-chain aliphatic compounds in film cover is decreased,free branched-chain aliphatic compounds is different with different years.In the isoprene metabolism pathway,the content of terpenes and isoprene compounds in free and bound all increased,because the grass competed water with the plants,which caused the plants being in a mild water stress environment,the content of terpenes and isoprene compounds decresed by film cover.4.The effect of grass and film cover on wine aromaThe experiments show that the content of aroma compounds in wine has changed by different treatments.the content of C6 alcohol of grass cover were decreased,while the content of higher alcohols,acetates,fatty acid ethyl esters,other esters,terpenes,carbonyl compounds,isoprene and volatile phenols were increased.The film cover reduced the content of fatty acids and isoprene,on the contrary,increased the content of acetate,fatty acid ethyl ester,other esters and carbonyl compounds.Combined with the analysis of the aroma profile,it was found that the grass and film cover treatments adds more fruity,floral and caramel fragrance in wine.In addition,the treatment of film cover also brought more plant flavor in wine.The results of principal component analysis(PCA)showed that the influence of years on aroma substances was greater than that of cultivation treatment,the years can distinguish well after alcohol fermentation and malolactic fermentation by principal components.In cultivation,grass cover can be distinguished from all treatments after the end of alcohol fermentation and the end of malolactic fermentation,and the main substances to be distinguished are terpenes(geranyl acetone,linalool and citronellol).The film cover can also be distinguished from the all treatments after alcohol fermentation.the main substances to be distinguished are C6 alcohol(cis-3-hexenol,trans-2-hexenol),higher alcohol(3-methyl-1-pentanol,cis-6-nonyl alcohol),but the film cover can not be distinguished from the control group at the end of malolactic fermentation.