Comparative study of yak and cow milk fermented with auxiliary cultures: Physicochemical, microstructural, and flavor profiles.

Fermented milk is a product in daily use that faces many challenges, including natural flavor, good texture, and improvement of health benefits. In this study, Leuconostoc mesenteroides and Saccharomyces cerevisiae were employed as auxiliary fermenters to solve these challenges. After fermentation, both cow fermented milk and yak fermented milk showed comprehensive fruit flavors, and GC-MS/MS demonstrated that the generation of 19 kinds of volatile compounds including esters, ketones, aldehydes, and acids are major contributors and mainly provide fruit, flower, and coconut flavors. For instance, isoamyl acetate and ethyl caprylate, increased by 164.20 ± 8.04 µg/kg and 115.53 ± 13.49 µg/kg in the experimental cow milk formulation (CME) after the addition of auxiliary fermenters. Meanwhile, the concentration of off-flavor volatile compounds, such as 3-methyl-2-butenal (roasted flavor), decreased or degraded with fermentation using auxiliary fermenters. At the same time, fermented milk with auxiliary fermenters showed improved texture, especially in firmness, which increased by 1.28% and 27.7% for CME and experimental yak milk formulation (YME), respectively. The results of scanning electron microscopy also proved that the protein network was thicker, with smaller gaps and larger clusters, with auxiliary fermenters compared with the control. The milk fermented with auxiliary fermenters increased water-holding capacity by 73.33% and 98.47% for CME and YME, respectively, and showed greater total acceptance than the control.