Abstract:

Four Lactobacillus strains (LP1, LP2, LP3, and LP4) with excellent fermentation performance isolated from
homemade yak yogurt samples collected in Tibetan plateau pastoral areas were used in combination to ferment yak yogurt.
Using the disc diffusion method, the combination of LP1 and LP2 was screened as the best culture starter for the production
of yak yogurt in terms of coagulation time, titratable acidity and sensory evaluation. The optimum fermentation parameters
for yak yogurt were obtained through an orthogonal array design L16 (44) as follows: fermentation temperature, 42 ℃;
inoculum amount, 6%; sugar concentration, 4 g/100 mL; and LP1 to LP2 ratio, 2:1. Under these conditions, the fermented
yak milk revealed even solidification, delicate and smooth texture, no whey separation and rich yogurt flavor.

Key words: yak yogurt, Lactobacillus, mixed-culture fermentation, process optimization