| Vinegar is a common condiment that has a huge market because of its unique taste and flavor and a wide range of application scenarios.There are many kinds of vinegar on the market,and there are differences in the raw materials and brewing processes of vinegar brewing in different regions,resulting in the formation of vinegar varieties with different aromas.At present,the aroma analysis of vinegar mainly uses gas chromatography-mass spectrometry detection,gas chromatography olfactometry,sensory analysis,and so on,the steps are more and longer,and it has not been shown that through the volatile components fingerprint of vinegar,the different vinegar species at home and abroad,the differentiation between brewing vinegar and delineating vinegar and the aroma analysis of vinegar.In this paper,commercially available vinegar samples were rapidly detected by ultra-fast gas chromatography electronic nose(UFGC-Enose),and the aroma profiles of each sample were analyzed based on the volatile components and their contents,combined with different statistical methods to analyze and predict vinegar classes.This paper consists of the following three parts:(1)The commercially available vinegar,rice vinegar,and mature vinegar 3 categories,a total of 25 brands of fermented vinegar are detected using UFGC-Enose.First,the optimal detection conditions of e-nose were investigated by using the number of chromatographic peaks,peak shape,and response intensity as indicators.The volatile components were qualitatively and quantitatively analyzed by retention index,external standard method,and proximity retention time method,combined with odor activity values to compare the relationship between the differences in the volatile aroma of different kinds of vinegar and the contents of compounds.The differences in volatile compounds of vinegar were investigated with linear discrimination,random forest,principal component analysis,and orthogonal partial least squares discrimination in the hope of discriminating against vinegar.The results showed that a total of 41 volatile compounds were detected in the 3 types of vinegar,mainly including alcohols,esters,aldehydes,ketones,acids,alkanes,and heterocycles.Acids were the most abundant in vinegar,followed by alcohols and aldehydes,while alkanes were the least abundant.Odor activity values and odor radar plots of vinegar samples illustrated that acetic acid,propionic acid,3-methylbutanal,phenylacetaldehyde,nonanal,decanal,and guaiacol contributed greatly to the aroma.The oil cheese,nut cocoa,fruit,and sour notes of aroma vinegar were prominent,the sour and floral notes of mature vinegar were prominent,while the volatile aroma other than the sour note of rice vinegar was weak.Linear discriminant analysis showed that vinegar of the same kind and different brands also differed in its aroma profile and volatile composition;The classification accuracy of the random forest model after training on vinegar samples can reach 100%,benzaldehyde,and3-methylbutanol,etc.can be used as important compounds to distinguish vinegar species;The discriminability of vinegar was further proved by principal component analysis and orthogonal partial least squares discriminant model.(2)The commercially available 11 different kinds of vinegar from European countries were analyzed using the UFGC-Enose and qualitative and quantitative analysis of the detected volatile compounds were carried out,combined with odor activity values to construct an odor model of vinegar,to find key compounds that provide aroma in each vinegar.The differences among the 11 vinegar species were initially observed by principal component analysis,and orthogonal partial least squares were used to explore the differences among different kinds of vinegar,as well as the signature volatile compounds.A total of 83 volatile compounds,mainly comprising acids,alcohols,esters,aldehydes,and heterocycles,were detected in the 11 vinegar samples.The levels and amounts of volatile compounds other than acids were higher in vinegar brewed from apples and wines than in that brewed from other raw materials.A total of 61 volatile compounds with odor activity values greater than 1 were identified,among which acetic acid,ethyl isovalerate,propionaldehyde,butanoic acid,ethyl cinnamate,and guaiacol contributed significantly to vinegar aroma,fruity and floral notes of wine vinegar and balsam vinegar were more obvious,and woody and cream notes of apple vinegar were equally prominent,whereas vinegar brewed with sugar beet,sugarcane or malt had an aroma that was only sour and univocal.The results of the principal component analysis showed that there were obvious differences in the individual samples of vinegar;the orthogonal partial least squares method can effectively distinguish vinegar brewed from different kinds of raw materials,and 10 marker volatile components including acetic acid,pyrazine,and ethyl acetate were screened out.(3)UFGC-Enose was used for the detection of commercially available brewing vinegar vs.delineated glass vinegar,and the detected volatile compounds were qualitatively and quantitatively analyzed.Orthogonal partial least squares discriminant and random forest methods were used for discrimination of brewing vinegar from delineation vinegar,and differences in vinegar samples of different grades of raw materials were observed;A mathematical model of brewing vinegar vs.collusion vinegar was established using linear discriminant method.A total of 32 volatile components,containing alcohols,esters,aldehydes,acids,heterocycles,and phenols,were detected in the 20 vinegar samples,of which the largest variety of volatile components was detected in samples containing cereals from brewing vinegar,the samples fermented with edible alcohol had fewer components,and the samples prepared with glacial acetic acid had the fewest components;Ligustrazine and nonyl acetate were the most abundant in delineated glass vinegar,while the remaining volatile components were the most abundant in brewing vinegar.Orthogonal partial least squares discriminant analysis of vinegar samples of different grades of raw materials could be well distinguished,and brewing vinegar samples were clustered more centrally,and 12 volatile markers of different kinds of vinegar were screened out by their variable importance for the projection values.In random forest analysis,the predicted classification accuracies of brewing vinegar and delineated glass vinegar were 100%,and six volatile markers including acetic acid,methyl isobutyrate and ethanol were screened out based on the Gini coefficient;The predicted classification accuracy by raw material grade could also reach 100%,and its screened volatile markers were consistent with orthogonal partial least squares discriminant analysis.In the linear discriminant analysis model,a mathematical model was established to distinguish brewing vinegar from delineation vinegar using the volatile component content as the independent variable,which was defined as brewing vinegar when the discriminant function y-value of this sample was greater than 0(1.14 ? 5.44);However,it was defined as colluding vinegar when the y-value was less than 0(-10.67 to-7.22)... |
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