Analysis And Formation Mechanism Of Flavor Substances In Yeast Products

Yeast is widely used in daily life.Yeast extract(YE)and yeast powder are made from yeast.YE is a natural spice with rich nutrition and unique flavor,while yeast powder is the main starter of Chinese steamed bread(CSB)as the traditional staple food and has a great influence on the flavor of CSB.Therefore,different yeast powder samples,YE samples and CSB from different fermentation stages were analyzed to explore the key flavor substances and their formation mechanism.The main results were as follows:(1)Eight kinds of yeast powder were extracted by SPME combined with SAFE to be analyzed on the GC-MS with qualitative and quantitative analysis,a total of 44 key aroma compounds were identified,which were mainly divided into alcohols,aldehydes,acids,esters,phenols and sulfur compounds.Among them,(E,E)-2,4-decadienal(OAV=1550),?-nonanolactone(OAV=285),isoamyl acetate(OAV=121),isoamyl acetate(OAV=208),?-decalactone(OAV=118),indole(OAV=58),eugenol(OAV=117)and indole(OAV=966)were the key odor substances in CY0220,CD0509,CL10801,CY0541,CD0524,CF816,CD0502 and CF1512,respectively.The sensory evaluation results also showed that there were significant differences among the 8 yeast powders.Compared with other samples,CF816,CD0524,CL10801,CF1512,and CD0502 were the most prominent in delicate fragrance,sweet,rancid,yeasty and sour attributes.(2)Gas chromatography-olfactometry coupled with sensory analysis and partial least-squares regression(PLSR)analysis led to the identification of the odorants responsible for the different flavors of four yeast extracts.Sensory analysis showed that LA00 L had an intense sulfurous attribute,and LA00 was characterized by fatty and green notes,FA31 exhibited the floral odor,while KA02 had strong phenolic,animal,fermented,roasted,and caramellic notes.A total of 37 key aroma compounds with odor activity values greater than1 were determined.2,4-Di-tert-butylphenol and methional were the most potent aroma compounds(FD=1024).In addition,the recombination results showed that the key aroma compounds in LA00 L were nonanal,dimethyl disulfide,and ?-decalactone.Octanal,dimethyl disulfide,and benzeneacetaldehyde were the key aroma compounds in LA00.In FA31,styrene,benzeneacetaldehyde,and acetophenone were the key aroma compounds,while indole,2-methoxyphenol,benzeneacetaldehyde,and p-cresol contributed significantly to the aroma of KA02.PLSR showed that p-cresol and indole were significantly responsible for the phenolic and animal notes inducing the off-flavor(yeasty odor)of yeasty extracts.More significantly,indole was first reported to have an important effect on yeasty odor.(3)Three kinds of yeast powder(CF1303,CF1318 and CL10138)were used to make dough and CSB at different fermentation stages(0.5 h,1.0 h,1.5 h and 2.0 h).For dough,the p H increased while the total titratable acidity(TTA)decreased with the fermentation progressing.There were differences in microbial diversity in dough at different fermentation stages.the results of fungal diversity showed that the main fungi were Saccharomyces cerevisiae,and the effect of fermentation time on the fungal diversity was greater than that of yeast powder itself.The results of bacterial diversity showed that the difference among samples was greater than the effect of fermentation time on bacterial diversity in dough.Among the bacteria,the main bacteria were Pantoea and Rhodococcus.The results of electronic nose of dough and steamed bread in different awakening stages showed that the effect of awakening time on the flavor of dough and steamed bread was greater than that of yeast itself.Through SAFE-GC-MS analysis,81,46 and 44 volatile compounds were identified in CF1303,CF1318 and CL10138 dough,53,66 and 34 volatile compounds were identified in steamed bread,24 volatile compounds were identified in flour and 30 volatile compounds were identified in steamed bread blank.The composition and content of volatile aroma compounds in dough and steamed bread were different in different awakening stages,and the content of phenylethanol in dough and steamed bread increased with the increase of awakening time.The description words of sweetness,yeast flavor,milk flavor,wheat flavor,sour taste,wine flavor,flour flavor and sweetness used in the sensory profile of steamed bread were used in the description of the sensory profile of steamed bread by multivariate analysis.The flavor profile of steamed bread with the same active dry yeast powder was different in different awakening time,and the yeast flavor was enhanced with the progress of fermentation;the sensory results of different yeast steamed bread at the same awakening time were also different,the sweetness and sweetness of CF1303 were prominent,the milk flavor,wheat flavor and yeast flavor of CF1318 were prominent,and the sour,wine and flour taste of CL10138 were prominent.AEDA results showed that phenylethanol(FD=1024)was the most important aroma compound in yeast steamed bread.CF1303,CF1318 and CL10138 contained 24,22 and 21 key aroma compounds,which were guaiacol(OAV=5054),acetophenone(OAV=1543),2,3-butanediol(OAV=1274)and 3-methyl-1-butanol(OAV=1119),respectively.Nonanal(OAV=10462),?-myrcene(OAV=4340),2,3-butanediol(OAV=2141),D-limonene(OAV=1938);3-methyl-1-butanol(OAV=1160),2,3-butanediol(OAV=911),and pentanol(OAV=902).The key aroma compounds specific to CF1303,CF1318 and CL10138 were guaiacol;?-myrcene,nonanal and methyl cinnamate;2-methylbutyric acid,respectively.