Lactase Activity of Cultured and Acidified Dairy Products

A method was standardized for determining lactase activity in cultured and acidified dairy products such as cottage cheese, sour cream, and yogurt. Cottage cheese and sour cream prepared by both the cultured and acidified processes and yogurt prepared by the direct acidification process did not possess lactase activity. However, cultured yogurt possessed considerable enzyme activity mainly due to lactase as an endoenzyme in the yogurt culture (Lactobacillus bulgaricus and Streptococcus thermophilus). Enzyme in yogurt increased with time of incubation, reaching a maximum of 8 orthonitrophenol β-d-galactopyranoside units per gram of yogurt in 4 h. S. thermophilus contained approximately three times more lactase than did L. bulgaricus. Also, an in vitro digestion process appeared to enhance the release of lactase from the composite yogurt culture. It was felt that cultured yogurt would be beneficial to individuals suffering from lactose intolerance not only because of reduced lactose but also because of lactase.