Flavor characteristics of natural yak yogurt and the impact of fermentation with isolated strains on flavor compounds in manual yak yogurt

Abstract

Northern Qinghai Lake is a unique natural ecological pastoral region, imparting a distinctive flavor to natural yak yogurt. This study aimed to investigate the role of Lactic acid bacteria (LAB) in the formation of key flavor compounds in yak yogurt. Using an electronic nose and gas chromatography-mass spectrometry (GC-MS), the flavor profile of yak yogurt was characterized. The characteristic flavor compounds in natural yak yogurt made by herders include 2,3-pentanedione, hexanal, 2,3-butanedione, 3-methyl-1-butanol, and heptanal. A total of 34 LAB strains were isolated, with Streptococcus thermophilus identified as the dominant strain (85.3 %). S. thermophilus, Limosilactobacillus fermentum, Lacticaseibacillus paracasei and Lactococcus lactis were used for manual fermentation of yak yogurt, with S. thermophilus proportions set at 25 %, 45 %, 65 %, and 85 %. The results revealed that key characteristic flavor compounds in manual yak yogurt included pentanal, 2,3-butanedione, acetoin, and 1-pentanol. Notably, 2,3-butanedione was a distinguishing compound in both natural and manual yak yogurt, with its concentration increasing proportionally with the addition of S. thermophilus in the starter culture. These findings demonstrate that S. thermophilus plays a pivotal role in the formation of 2,3-butanedione, a key flavor compound in yak yogurt, highlighting its importance in defining the unique sensory attributes of the product.