Cell-envelope proteinase from Lactobacillus delbrueckii subsp. bulgaricus affects the gel properties of fermented milk

Abstract

The proteolytic activity of Lactobacillus delbrueckii subsp. bulgaricus has been shown to affect the formation and stability of fermented milk. In the present study, the effects of purified cell-envelope proteinase (CEP) from L. bulgaricus on the quality of fermented milk were investigated (20 U g−1 protein). The CEP of L. bulgaricus could significantly increase gel hardness and consistency of fermented milk. The particle size of aggregates was significantly increased, and the negative charge of milk protein surface was significantly decreased. Hydrolysis with the purified CEP significantly increased the free Ca2+ levels and decreased the casein bound Ca2+ levels within gel networks. CEP treatment produced fermented milk with small holes in a uniform and closely connected structure. For the rheological properties, CEP of L. bulgaricus S3 increased viscosity and shear stress, whereas CEP from L. bulgaricus C3 increased the strength of the gel and gave milk gel a higher G′ value.