| Colloidal haze is a complicated phenomenon that commonly happened in Huangjiu during its shelf time,and therefore exerts a serious impact on its appearance and also a bad impression to consumers.Previous studies have confirmed that the main components of turbidity in Huangjiu were wheat proteins.In order to further understand the formation process of haze,the following analysis were performed:The protein constitutions in bottled Huangjiu were illustrated by 2DE separation following MALDI-TOF/TOF MS identification.Proteins originated from wheat and rice,such asα-amylase inhibitor 0.19,avenin-like proteins,pathogenesis-related protein,seed allergenic protein RAG2,andα-amylase/trypsin inhibitor RA16 were the main components.Half of the protein spots were identified as wheatα-amylase inhibitor.In addition,the variations of protein constitution in different fermentation stages of Huangjiu were analyzed.At the beginning of fermentation,proteins from the raw material could be mostly dissolved in the fermentation broth.In the following 3 days of fermentation,the protein profile remained unchanged.However,in the 4 days of fermentation and thereafter,some of protein bands were gradually decreased or disappeared.As fermentation terminated,there were only 9 protein bands left,which were identified asβ-amylase,endochitinase C,endogenousα-amylase/subtilisin inhibitor,α-amylase inhibitor 0.19,wheatwin1,and lipid transfer protein from wheat Qu,and riceα-amylase/trypsin inhibitor,respectively.Theα-amylase inhibitor was purified from wheat Qu and bottled Huangjiu respectively,by a combination of ammonium sulfate precipitation,anion exchange column as well as gel filtration column.The purifiedα-amylase inhibitor was then added to the bottled Huangjiu for investigating of its effect on turbidity formation in the rice wine.It was found that there was a most serious turbidity with the supplementing titer of 9 g·L-1.Infrared spectroscopy analysis showed thatα-amylase inhibitor was a glycoprotein.The ethanol precipitated sample was hydrolyzed with 2 M TFA to identify monosaccharide composition by gas chromatography–mass spectrometry.The results showed that Chinese rice wine is rich in glucose.In addition to glucose(44.38 mg·L-1),other monosaccharide fractions were xylose,arabinose,mannose,and galactose. |
