The Fingerprints Construction Of Volatile Flavor Compounds Of Milk Fermented With Lactobacillus Delbrueckii Subsp. Bulgaricus

Lactobacillus delbrueckii subsp.bulgaricus is one of the basic strains in yogurt starter and is widely used in the industrial production of various dairy products.In this study,17 Lactobacillus delbrueckii subsp.bulgaricus strains that were separated from traditional dairy products in Mongolia,Tibet,Xinjiang and et al,were used as experimental strains.Apart from the fermentation characteristics,we also used SPME-GC-MS technology to detect and analyze volatile flavor substances in fermented milk at the end of fermentation to select strains with excellent flavor.Based on that,the differences of the main volatile flavor substances were analyzed.The results are as follows:1.By studying the fermentation characteristics of 17 strains of Lactobacillus delbrueckii subsp.bulgaricus in milk,it was found that IMAU20402(B1),IMAU20360(B3);IMAU20220(B6),IMAU20234(B9),IMAU20769(B10),IMAU20775(B11),IMAU20421(B13),IMAU20312(B14)and IMAU62081(B16)had shorter fermentation time compared with the control strain C,especially the IMAU20220(B6),reaching the fermentation time in 8.2 h;during the fermentation and storage(12 h),the titratable acidity of most strains was always less than 110°T;the viable counts of the fermented samples of IMAU20402(B1),IMAU20403(B2)and IMAU62081(B16)increased remarkably,and were close to the control sample(7.15 X 108 CFU/mL)at the end of the fermentation.What's more,the viscosity of the fermented milk samples of all the tested strains was different significantly,among them,IMAU20228(B8)with the highest value,the viscosity of the sample reached 1207 and 1805 mPa.s at the end of fermentation and storage for 12 h.It was better than control strain.2.At the end of the fermentation,92 volatile flavor substances were detected in the samples of 18 strains,including acids(18),aldehydes(14),ketones(13),alcohols(30),esters(8)and alkanes(10)compounds.Among them,the OAV of 11 flavor compounds(acetaldehyde,3-methyl butanal,(E)-2-pentenal,hexanal,(E)-2-octenal,furfural,2,3-butanedione,acetoin,2-Heptanone,2-nonanone and vinyl formate)was not less than 1,which contributes to flavor of the fermented milk greatly.The three flavor compounds of 3-methyl butyric acid,1-hcptanol and n-hexanol with an OAV value of more than or equal to 0.1,so it's also an important modification effect on the flavor.3.The GC-MS technique was used to analyze the flavor substances in all tested strains.It was found that the fingerprints of all samples had good repeatability,and the similarity of parallel samples was between 0.92-0.97.It shows that the established fingerprint is accurate and reliable,which can be used for the construction and quality evaluation of the fingerprint of flavor substances in milk fermented by different strains.The similarity between the samples(control strain C,IMAU20364(B4),IMAU20220(B6),IMAU20227(B7),IMAU20775(B11),IMAU20790(B12),IMAU20312(B14)and IMAU62081(B16))and the reference fingerprint was greater than 0.8,indicating that all samples have a good similarity.4.The flavor substances of 17 Lactobacillus delhrueckii subsp.bulgaricus in fermented milk and control strain C were detected by GC-MS,and the data was analyzed by principal component analysis(PCA).It was found that the aldehyde compounds showed a high correlation with IMAU20234(B9),IMAU20775(B11),IMAU20790(B12),IMAU20421(B13)and IMAU32104(B15),and the ketone compounds showed a high correlation with the control strain C,IM AU20402(B 1),IMAU20364(B4),IMAU20220(B6),IMAU20228(B8),IMAU20312(B 14),IMAU62081(B16)and IMAU62115(B17);the acid compounds showed a higher correlation with IMAU20790(B 12);the alcohol compounds showed a higher correlation with IMAU20396(B5),and the alkane compounds showed a higher correlation with IMAU20403(B2),IMAU20360(B3)and IMAU20769(B10).5.Through the sensory evaluation,the determination of fermentation properties and the analysis of volatile flavor substances in fermented milk at the end of fermentation of the control strain C and 17 Lactobacillus delbrueckii subsp.bulgaricus,it was found that IMAU20312(B14)and IMAU62081(B16)have good fermentation characteristics and excellent flavor.Thus,they can be used as yogurt starter in dairy processing.