Effect Of High Pressure On Main Volatile Compounds And Aging Characteristics Of Mild Aromatic Chinese Liquor

Aging is an essential procedure in the manufacture process of Chinese liquor,but the conventional way of aging requires long production cycle and large factory area,which is adverse to improving production efficiency and reducing production cost.The essence of aging is a series of physical and chemical reactions that volatile compounds in Chinese liquor undergo during storage.This work focused on changes of volatile compounds in Chinese liquor after high pressure treatment and a combination of high pressure treatment and following storage comparing with natural aging process.With gas chromatography and electronic nose,the aging effect of high pressure treatment on Chinese liquor was evaluated using multiple models including principle components analysis,cluster analysis,linear discriminant analysis and partial least square regression.Main results are as following:1.Volatile compounds changed dramatically during the first year of natural aging process,and tended to be relative stable in the following three years,but big changes were observed again in the fifth year.Though the majority of acids,esters,alcohols and aldehydes decreased significantly during natural aging process,increases in propionic acid,phenylethanol and ethyl palmitate were observed,while ethyl lactate was rather stable as no significant change was found.2.The overall differences in volatile compounds between Chinese liquor with different ages were obvious.Results from principle component analysis and quantitative analysis based on volatile compounds showed that the increase in ethyl palmitate,and decreases in acetaldehyde,ethyl acetate,acetal and acetic acid could be regarded as the sign of aging.3.After being treated by high pressure less than 300 MPa,no significant change was found in volatile compounds of Chinese liquor.As for higher level of treatments,the effects of 400 MPa and 500 MPa of high pressure were comparable with the one of 300 MPa.To optimize the processing effect and economic cost,400 MPa-15 min and 400 MPa-30 min were used as high pressure parameters.4.High pressure treatments decreased the contents of alcohols and aldehydes,which is consistent with natural aging process,but had no significant effect on acids and esters.Evalution on volatile compounds demonstrated that high pressure treatments narrowed the overall difference between young liquor and one-year aged liquor,though there was still a big gap between these two groups.5.Electronic nose generated stable and repeatable signals in response to volatile compounds in Chinese liquor with different ages,which indicated significant difference between groups.Liquor age classification and identification were achieved using linear discriminant analysis,with accuracy of 98.3% among 120 samples.As for liquor age prediction,the correlation coefficients in traning set and validation set reached 0.9732 and 0.9101,respectively.Quantitative evalution using this prediction model showed that high pressure treated liquor was comparable with one-month aged liquor in terms of aging characteristics.6.Two months and six months of storage experiments indicated that high pressure treatments had no effect on volatile compounds in Chinese liquor during the subsequent storage process,no significant difference was observed between young liquor and high pressure treated liquor after storage.7.Based on storage experiments,we proposed a theoretical mechanism for changes of volatile compounds during aging process.Considering the essence of aging is a series of physical and chemical reactions,initially,volatilization and permeation are key factors which have significant effect on changes of volatile compounds since the rate of chemical reactions are relative slow;as all volatile compounds decrease,volatilization rate slows down as well,thus,chemical reactions including esterification and oxidation gradually play a more dominant role in the aging process.This well explains the phenomenon that all volatile compounds decresed dramatically at the early stage and tended to be relative stable,increase trends were even observed in some volatile compounds.However,more evidences are needed to verify this hypothesis.