Rheological Properties of Yogurt Made with Encapsulated Nonropy Lactic Cultures

Abstract

Rheological properties were determined for skim milk that had been fermented with ropy cultures, nonropy encapsulated cultures, and nonropy unencapsulated cultures. Reconstituted NDM was cultured with single strains or combinations of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus at 37°C until the desired pH (4.6 for single-strain yogurt and 4.2 for mixed-strain yogurt) was attained. Yogurt made with encapsulated nonropy strains had higher shear stress values than yogurt made with unencapsulated nonropy strains. Ropy strains produced yogurts with the highest shear stress values. The consistency coefficient (upward flow) and apparent viscosity (downward flow) of yogurt made with encapsulated nonropy strains were higher than those of yogurt made with unencapsulated nonropy strains. Encapsulated nonropy mixed cultures produced yogurt that had a higher stability index than that of yogurts made with ropy and unencapsulated nonropy strains. Bacterial capsules might cause weak points within the gel structure, resulting in a product with lower values for shear stress. Although both types of polysaccharides (capsular and ropy slime) influenced the rheological properties of yogurt, each produced different effects. Slime polysaccharides produced a stretchable structure unlike capsular polysaccharide, but both polysaccharides increased viscosity.