Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus with different fermentation characteristics were individually or composite cultured to investigate their storage stability, including the acidity, viscosity, water-holding capacity and flavor compounds of fermented yoghurt. The results showed that the acid production rate of yoghurt fermented by S. thermophilus HST-6, HST-9 and L. delbrueckii subsp. bulgaricus KDB-1 was fast. Within 14 days of storage, acidity, viscosity and water-holding capacity were 98.10 °T, 9 498.33 MPa·s and 98.51%, respectively, and the stability was significantly higher than that of other strains (P<0.05). At the same time, the sensory score of the product was the highest. The results of SPME-GC-MS analysis showed that the main volatile flavor compounds of yoghurt fermented by three strains were different from those fermented by single strain during storage. A total of 108 volatile compounds were detected in yoghurt, including aldehydes, ketones, acids, esters, alcohols, aromatics and alkanes. The 2-nonone, 2-heptanone, 1-octanol, acetoin, tert-hexadecanethiol were the main flavor compounds in yoghurt. The composite fermentation of three strains has potential industrial application prospects as yoghurt starter.
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