Analysis Of Volatile Flavor Compounds In Fermented Milk And Research For Its Chromatographic Fingerprints

Streptococcus thermophilus and Lactobacillus delbrueckii subsp.bulgaricus were crucial starter strains on account of giving the fermented milks with good flavor and texture.In this study,Solid phase microextraction and gas chromatography coupled with mass spectrometry(SPME-GC-MS)werer applied to analyse the volatile flavor compounds in fermented milk with the strains of S.thermophilus and L.delbrueckii subsp.bulgaricus.After screening out the starter with proper raio and good quality in fermentation and flavor,we deteceted the volatile flavor compounds through the period of whole fermentation and storage.We also discussed the key aroma compounds of every period by means of odor activity value(OAV)coupled with principal component analysis(PCA).Meanwhile,similarity analysis were carried out to study the chromatographic fingerprints of differernt starter strains and various starter ratios as well as every period in fermentation and storage.The main results were listed as follows:1.SPME-GC-MS were used to study the volatile flavor compounds of nine grous of fermented milk with different starter strains.The result showed that eighty-seven volatile flavor compounds,including aldehyde compounds,ketone compounds,acid compounds,esters compounds,alcohols compounds,nitrogen-containing compounds,hydrocarbons and aromatic compounds were detected.Among the L.delbrueckii subsp.bulgaricus IMAU 20401 coupled with S.thermophilus IMAU 40133 showed the features of shorter fermentation time,producing larger amount of acid and generating more abundent flavor compounds.2.The starter strains L.delbrueckii subsp.bulgaricus IMAU 20401 and S.thermophilus IMAU 40133 fermented in the proportion of 1:],1:10 1:50,1:100.1:1000 and 1:10000 produced around a hundred flavor compounds,what's more,the fermented milk in proportion of 1:1000 showed the characteristics of weaker post-acidification and richer flavor compounds compared with other proportions.3.When the starter strains L.delbrueckii subsp.bulgaricus IMAU 20401and S.thermophilus IMAU 40133 fermented in the proportion of 1:1000 could produced around ninety-eight flavor compounds in the period of fermentation and storage.The PCA result showed that pentanal,hexanal,heptanal,octanal,nonanal,2-nonanone and(Z)-2-octen-l-ol were the key aroma species of early stage of fermentation;acetaldehyde and(E)-2-decenal were the key aroma compounds in complete phase of fermentation;3-methyl-butanal,(E)-2-octenal,3-methyl-pentanoic acid and 1-octen-3-ol were the key aroma species at the beginning of the storage;whereas formic acid hexyl ester,formic acid ethenyl ester,1-octen-3-ol and 3-methyl-1-butanol were the key aroma compounds in later stage of storage.4.The similarity evaluation results suggested that the mixed strains species showed less affect,while the change of the starter ratios represented a greater affect Also the GC fingerprints would change gradually along with the process of fermentation and storage.In the process of fermentation and storage,the composition and content as well as the key aroma compounds showed significant different.