Study On The Relationship Between Tannin Structure And Characteristic Quality Of Dry Red Wine From Major Regions In Western China

As the most basic sensory characteristics of dry red wine,astringency is influenced by acid,reducing sugar,alcohol,total phenols,tannin and other factors.Among them,condensed tannin is the main substances causing astringency.Condensed tannin,due to their different structural components,can make wine shows different astringency qualities such as silky,velvety,drying,grainy,coarse and puckery.In order to explore the relationship between astringency quality and its components in wine,dry red wines from Xinjiang,Inner Mongolia and Gansu provinces in different vintages were selected as experimental wine samples.To better reflect the sensory quality of wine,the relationship between the structural characteristics of condensed tannin and astringency evaluation was constructed by combining chemical analysis(phyto-chemical indexes,polyphenols and tannin indexes)and sensory analysis(astringency intensity and astringency quality).The main results were as follows:(1)With the extension of aging time,the anthocyanin content in wine decreased gradually,and the color intensity and hue of wine generally showed a gradual increase trend.Also the purple tone of young wine samples was more obvious,while the yellowish brown tone of wine samples with longer aging time would gradually appear and deepen.However,other phyto-chemical indexes and polyphenols had no obvious change trend with time.(2)The total tannin content of wine simples decreased gradually with the aging time,and its content is affected by the region and variety of grape.The content of flavan-3-ols monomers in wines from different regions and years was different,and catechin(C)and epicatechin(EC)were the two most abundant monomers.Among the tannin components after phloroglucinol acid hydrolysis,C and EC were the main terminal units and extension units,respectively.Their average degree of polymerization ranges from 1.76 to 4.16,and increases with aging time.In terms of its structural characteristics,the proportion of procyanidins(%PC)was the highest,that of prodelphinidins(%PD)was the second,and that of galloylation(%G)was the lowest.Also,the tannin structure of wine aged 7-8 years tended to be stable.(3)The astringency evaluation of different wine samples showed that after aging,the astringency caused by condensed tannins was softer,and the color,aroma,taste of wines were more pleasant.Principal component analysis between astringency intensity and tannin structure showed that the dry astringency intensity of wine would be enhanced with the increase of total tannin content and average degree of polymerization.The higher content of EC in extension units would increase the dry astringency,while the higher content of epicatechin-3-O-gallate(ECG)in the terminial unit wpuld increase the velvety astringency.In addition,the changes of C in extension unit,C and EC in terminial unit would affect the overall sensory evaluation of wine samples.Among its structural characteristics,the increase of % PD would enhance the dry astringency,while the effect of galloylation degree on dryn astringency was relatively low.There were differences in the quality of wine astringency in different regions.The dry astringency in Xinjiang region was stronger,the velvety astringency of Inner Mongolia region was stronger,while the astringency in Gansu region is relatively balanced,and its overall evaluation was higher.