Characterisation Of Bound Volatile Compounds Of Kiwi And The Regulation Of Its Wine Aroma

Kiwi wine is a new type of alcoholic beverage,which contains rich nutrients such as phenols,amino acids,vitamins.Total phenolics,antioxidant activity and aroma of kiwi wine are influenced by fermentation processes and kiwi fruit varieties.At present,the deficiency of aroma has been one of the factors restricting the quality improvement of kiwi wine.While there are two forms of aroma substance in the fruits,one occurs in free form,in which they contribute directly to fruit and wines flavor;the other exists in their odourless bound form as the flavor precursors which can be transformed into volatile compounds by hydrolysis.In this experiment,with Actinidia deliciosa ‘Hayward',‘Xuxiang' and A.chinensis‘Hort16A' as raw material,the content of polyphenol compounds,antioxidant activity and free volatiles of kiwi wines fermented with pomace and through pure juice respectively were investigated.The bound aroma in kiwifruit and kiwi wine was also conducted.Meanwhile,the aroma precursors in kiwi pomace were applied to improve the quality of kiwi wine.The main results are as follows:(1)Fermentation methods and varieties had certain influence on contents of polyphenols.Wines fermented with pomace had higher content of polyphenols,yet the content of total phenolic in ‘Xuxiang' and ‘Hort16A' wines fermented with pomace were lower.This phenomenon illustrated that the fermentation with pomace can make active substances in pomace into wines.Antioxidant activity of kiwi wines was positively correlated with total phenolic content.Gallic acid,chlorogenic acidand(+)-catechin were the dominant individual phenols in kiwi wines.(2)The free volatile compounds in kiwi wine were analyzed by Headspace Solid-Phase Microextraction coupled with Gas Chromatography Mass Spectrometry.A total of 78 compounds were identified in kiwi wines,in which alcohols,esters and terpenoids were the major compound classes.The wine fermented with pomace has higher content of esters and terpenes classes,while the total content of free aroma in the wine fermented through pure juice was higher.Benzyl alcohol,isoamyl alcohol,2-methyl-1-butyl alcohol,ethyl acetate,phenyl ethyl acetate,isoamyl acetate,ethyl caproate,ethyl caprylate and decanoic acid ethylester were main free aroma components in kiwi wine.(3)The bound aroma compounds in samples were separated by Amberlite XAD-2column chromatography and the bound aroma compounds were subjected to enzymatic hydrolysis before HSPM-GC-MS analysis.A total of 103 bound aroma compounds were identified in six samples,in which terpenoids,benzenoids and alcohols were the major compound classes.The kiwi pomace has the most numerously bound aroma,while kiwi wine showed the highest concentrations of bound aroma.The content of bound aroma in juice and poamce was higher in ‘Hayward' variety than in ‘Hort16A' variety,yet the content of bound aroma in wine of ‘Hayward' variety was lower.(4)The main bound aroma in kiwi fruit included 1-octene-3-ol,trans-2-hexenal,he xanal,tropone,3-hydroxylauric acid,benzyl alcohol,phenylethyl alcohol,?-damasceno ne,linalool,terpinen-4-ol and phenol.The main bound aroma in kiwi wine included 2-ethyl hexanol,mthylthiopropanol,linalool,isogeraniol,nonanoic acid,eugenol,2-meth oxy-4-vinylphenol,benzyl alcohol and phenylethyl alcohol.(5)The addition of bound aroma substances and enzyme into kiwi wine not only can reduce the loss in antioxidant activity,phenol and volatiles,but also increase the content of flavones and procyanidine in wine.Meanwhile,a significant increase in the concentration of terpene compounds in wine was found through addition of bound aroma substances,making kiwi wine aroma stronger and more coordinate.