Huangjiu is the most ethnically distinctive type of wine in China and is well loved by consumers.Volatile carbonyl compounds are important components of flavors of Huangjiu and play an important role in the classification and quality study of Huangjiu.The detection of volatile carbonyl compounds in Huangjiu is difficult due to their large variety and low contents,and the research and understanding of volatile carbonyl compounds in Huangjiu is not yet deep enough.In this study,we optimised the detection of volatile carbonyl compounds in Huangjiu,and applied it to the identification of Huangjiu.We explored the volatile carbonyl compounds that vary between different Huangjiu,and further investigated the changes in volatile carbonyl compounds during the production and storage of Huangjiu,and analyzed the effects of temperature and oxygen on volatile carbonyl compounds.The main results of this study are as follows:(1)A method based on PFBHA derivatization combined with HS-SPME-GC-MS was optimized for the determination of volatile carbonyl compounds in Huangjiu.The best parameters were:1.3 g/L of PFBHA in 5 m L of Huangjiu,incubation at 45°C for 5 min and extraction for 35 min.53 volatile carbonyl compounds in Huangjiu were detected by this method,and new substances in Huangjiu,glyoxal and methylglyoxal,were identified.The method was validated to have good linearity in all linear ranges(R~2≥0.996),with LOD ranging from 0.002 to 0.105μg/L,LOQ ranging from 0.007 to 0.317μg/L,precision<10%,and recoveries between 91 and 109%.Compared with traditional non-derivative methods,the detection of volatile carbonyl compounds has been greatly improved and the detection limit have been reduced.(2)The method was applied to analyze the differences in volatile carbonyl compounds in different Huangjiu,and to investigate the characteristic volatile carbonyl compounds in Huangjiu of different regions,different suger contents and different raw materials.The highest total amounts of Strecker aldehydes,furans and other carbonyl compounds were found in Huangjiu,and the contents of Strecker aldehyde and furan were generally high.The characteristics of volatile carbonyl compounds in Huangjiu from different regions differed significantly.Methional,octanal and 3-hydroxy-2-butanone were positively correlated with Huangjiu from Jiangsu region.Propanal and glyoxal were positively correlated with Huangjiu from Fujian region.5-Methylfurfural,acrolein,decanal and dodecanal were positively correlated with Huangjiu from Zhejiang region.(E)-2-Butenal,2-butanone,2-methylpropanal,2-methylbutanal,and hexanal were positively correlated with Huangjiu from Shanghai region.There were 26 volatile carbonyl compounds with significantly different contents in semi-dry Huangjiu and semi-sweet Huangjiu,of which 21 were different compounds.17 Volatile carbonyl compounds,including benzaldehyde,2-phenyl-2-butenal,2-methylpropanal,2-methylbutanal and 2-furfural were significantly higher in semi-dry Huangjiu than in semi-sweet Huangjiu.The contents of acrolein,decanal,glyoxal and methional in semi-sweet Huangjiu were significantly higher in semi-sweet Huangjiu than in semi-dry Huangjiu.There were 26 volatile carbonyl compounds with significantly different contents between rice Huangjiu and non-rice Huangjiu,including six different compounds.3-Methylbutanal,benzaldehyde,2-methylpropanal,2-butanone and 3-methyl-2-butanone were significantly higher in rice Huangjiu than in non-rice Huangjiu,and 3-penten-2-one was significantly higher in non-rice Huangjiu than in rice Huangjiu.(3)The changes in volatile carbonyl compounds during the production and storage of Huangjiu were studied.During the brewing process of Huangjiu,the total amount of volatile carbonyl compounds fluctuates,among which the contents of most volatile carbonyl compounds such as ethanal,2-methylpropanal,3-methylbutanal and phenyl acetaldehyde were highest at the beginning of fermentation,and decreases as fermentation progresses.The contents of volatile carbonyl compounds of acrolein,3-methylbutanal and phenyl acetaldehyde decreased after pressing,while(E)-2-heptenal,3-methyl-2-butenal and 2-nonanone increased instead.The increased content of furfural and 5-methylfurfural in Huangjiu after blending may be related to the addition of caramel color.While most of the volatile carbonyl compounds were lost after decoction due to high temperatures,the content of some volatile carbonyl compounds such as 3-penten-2-one and methional increased,suggesting that the production of these volatile carbonyl compounds may be closely related to the Maillard reaction.The above patterns suggest that the volatile carbonyl compounds in Huangjiu may came mainly from the raw materials and that the brewing processes such as fermentation,pressing,blending and decoction can affect the characteristics of the volatile carbonyl compounds.The pattern of changes in volatile carbonyl compounds during the aging of Huangjiu was further investigated and it was found that the contents of most volatile carbonyl compounds increased significantly during the aging process,while the content of methional and 2,3-butanedione decreased significantly during aged.The storage stage in general facilitates the accumulation of volatile carbonyl compounds in Huangjiu.The representative volatile carbonyl compounds in short-term aged Huangjiu include 6-methyl-5-hepten-2-one,phenyl acetaldehyde,methional and 2,3-butanedione,and the representative volatile carbonyl compounds in long-term aged Huangjiu include 23 substances including furfural,5-methylfurfural,benzaldehyde and glyoxal.(4)The effects of oxygen and temperature on volatile carbonyl compounds in aged Huangjiu were investigated.Increasing the frequency of oxygenation significantly increased the contents of volatile carbonyl compounds in Huangjiu,furfural,3-hydroxy-2-butanone,3-methylbutanal,2-methylbutanal,2-methylpropanal and acetophenone being the most influenced by oxygen,with their contents increasing significantly when the frequency of oxygenation was increased.Increasing the temperature also promotes the formation of volatile carbonyl compounds in aged Huangjiu,furfural,3-hydroxy-2-butanone,3-methylbutanal and benzaldehyde showed the most significant changes when the temperature of Huangjiu is increased.The correlation between Strecker aldehydes and their corresponding precursors during aging was investigated,and the pathways of Strecker aldehydes formation during aging were speculated.The results indicated that 2-methylpropanal,2-methylbutanal,3-methylbutanal and phenyl acetaldehyde may mainly come from the degradation reaction of Strecker,while benzaldehyde and methional may mainly come from the oxidation of higher alcohols during the aging process. |