The influence of whey protein concentrate (WPC80) added to fermented skim milk drink on its stability was studied. The stability of fermented skim milk drink with different concentrations of whey protein concentrate was evaluated by particle size distribution, centrifugal analysis and Turbiscan analysis. The results showed that fermented milk drink containing 30% WPC80 had the smallest particle size and smallest centrifugal sediment. The turbiscan analysis showed distinctly that the fortified drink produced less sediment than the fermented milk drink with no added WPC80.

ε-Polylysine is widely used as a natural biological preservative in meat, dairy products and other foods for its characteristics of high safety, stability, efficiency, solublity in water and broad-spectrum antibacterial activity. In this paper, physiological and biochemical characteristics of Streptomyces albulus UN2-71, a strain capable of producing ε-polylysine, were studied. The ε-polylysine production increased from 1.64 to 2.37 g/L after optimization of fermentation conditions. The optimized conditions were defined as: 30 mL of the liquid medium in a 250 mL shake flask, inoculum size 10%, temperature 30 ℃, shaking speed 150 r/min and initial fermentation pH 7.0.