关键词: 发酵乳杆菌；牦牛酸奶；香气组分；贮藏

Abstract: The probiotic strain Lactobacillus fermentum HY01 combined with the commercial starter culture MY105 of Streptococus thermophiles and Lactobacillus delbrueckii subsp. bulgaricus was used to produce fermented yak milk. The fermentation conditions were optimized through the combined use of one-factor-at-a-time method and response surface methodology, and the quality changes of the yogurt prepared under optimized conditions were observed during storage. The changes in aroma components at different post-ripening times were analyzed by electronic nose (EN). The results showed that the optimal process conditions were obtained as follows: HY01 inoculation amount 4%, fermentation temperature 40 ℃, and time 6 h, and the viable count of probiotics in the prepared yogurt was 8.90 × 108 CFU/mL and it scored 89.72 points in sensory evaluation. During the storage period of 28 days, the number of probiotics was maintained higher than 107 CFU/mL and the acidity lower than 118 °T. Texture properties (viscosity, hardness, consistency and cohesiveness), the contents of diacetyl and acetaldehyde and sensory score remained basically unchanged from day 0 to 14 d during storage, but decreased then. In addition, principal component analysis performed on the EN data showed that the characteristic aroma of yak yogurt was composed of nitrogen oxides, methyl compounds, sulfides and alcohols, whose contents were significantly different from those of the yogurt. Therefore, yak yogurt containing L. fermentum HY01 not only has good performance and flavor, but also is expected to be beneficial for intestinal health.

Key words: Lactobacillus fermentum; yak yogurt; flavor substances; storage