Study On The Variation Of Alkylpyrazines And Flavors During The Production Of Fermented Vinegar

Alkylpyrazine(APZ),an important flavor substance in foods,has attracted wide attention.Tetramethylpyrazine(TMP)belonging to APZ has become an important quality indicator of vinegar.However,there were little studies on the distribution and variation about other APZ in vinegar.The aims of this work were to study the variation of APZ during the processing of traditional fermented vinegar,discuss the effect of phenolic acid on TMP formation,and discriminate vinegar in different stages of production based on the modern sensory analysis technologies,which might provide a theoretical basis for the improvement of vinegar nutritional value and quality control.The study was as follows:(1)A simultaneous determination method for APZ in vinegar was established.The mobile phases were separately A(acetonitrile)and B(aqueous solution containing 0.1%formic acid and 0.1%trifluoroacetic acid),with the ratio of A to B being 1:99.Besides,the detection wavelength was 275 nm,and the column temperature was 35℃.The detection limit of the method was 0.016-0.084 mg/L,the quantitation limit of the method was 0.052-0.278 mg/L,and the recovery rate of the method was 96%to 110%,which indicated the method was sensitive and accurate.It had been applied to the analysis of commercial vinegars of different brands on sell.The results showed that there were significant differences in APZ of different vinegars.Dimethyl pyrazine and ethyl pyrazine were less in commercial vinegar while TMP was more.(2)The above detection method was used dto study the variation of APZ during vinegar fermentation and aging.The total content of APZ increased with the aged time.Pyrazine,monomethylpyrazine,dimethyl pyrazine and TMP arose in large amounts during aging in Monascus vinegar.Trimethylpyrazine and ethyl pyrazine increased slowly during the whole fermentation stage.The APZ in Shanxi aged vinegar largely arose in the stage of fumigating vinegar,but it decreased significantly during the period of drenching vinegar due to the dilution effect of the white fermented grains and water,and then slowly increased during the storing times.The content of APZ and the variation trend in the two vinegars were different because of the different fermentation processes.(3)Ammonium salt and acetoin model system were used to study the effect of different phenolic acids on the formation of TMP.The results showed that the type and concentration of ammonium salt affected the formation of TMP significantly.Phenolic acid could regulate the formation of TMP,which showed a dose-dependent effect in a certain concentration range(from 0.01%to 2%,measured by acetoin concentration).When gallic acid was added to 2%(measured by acetoin concentration),the TMP increased by 63.17%with reaction time of 24 h.At any pH,phenolic acid promoted the arising of TMP(P<0.05)and especially at pH 7.(4)The electronic nose,electronic tongue,GC-MS combined with PCA,CA and other statistical methods were used to evaluate Fujian Monascus vinegar in different fermentation stages and storing times.The results of electronic nose analysis showed that PCA and LDA could be used to distinguish Monascus vinegar in different fermentation stages and storing times.And the effect of LDA was better than the effect of PCA.The electronic tongue was used to analyze the changes in the taste of acid,bitter,salty,fresh,and astringent of vinegar.PCA analysis could identify Monascus vinegar in different fermentation stages and storing times.99 kinds of volatile components of Monascus vinegar in different fermentation stages and aging times were detected in vinegar and were discriminated by PCA and CA analysis.The above methods could discriminate different fermented and aging times of Fujian Monascus vinegar,especially for distinguishing vinegar of different aging times.