Lactose digestion by yogurt beta-galactosidase: influence of pH and microbial cell integrity.
Lactase-deficient subjects more effectively digest lactose in yogurt than lactose in other dairy products, apparently due to yogurt microbial beta-galactosidase (beta-gal) which is active in the GI tract. We evaluated the effects of buffering capacity of yogurt, gastric pH, and microbial cell disruption on beta-gal activity and lactose digestion. Three times more acid was required to acidify yogurt than to acidify milk. Yogurt beta-gal was stable at pH 4.0 but inactivated at lower pH. When yogurt was sonicated to disrupt microbial cell structure, only 20% activity remained after incubation at pH 4.0 for 60 min. In vivo gastric pH remained greater than 2.7 for 3 h after ingestion of yogurt. Acidified milk alone or with disrupted yogurt microorganisms caused twice as much lactose malabsorption as did acidified milk containing intact yogurt microorganisms. The results provide a possible explanation for the survival of beta-gal activity from yogurt in the GI tract.
D000328:Adult; D002021:Buffers; D002462:Cell Membrane / Q000502:physiology; D002473:Cell Wall / Q000502:physiology; D003611:Dairy Products; D004063:Digestion; D005696:Galactosidases / Q000378:metabolism*; D005745:Gastric Acidity Determination; D006801:Humans; D007778:Lactobacillus / Q000648:ultrastructure; D007785:Lactose / Q000378:metabolism*; D007787:Lactose Intolerance / Q000378:metabolism; D008297:Male; D013010:Sonication; D013291:Streptococcus / Q000648:ultrastructure; D015014:Yogurt; D001616:beta-Galactosidase / Q000378:metabolism*
D002021:Buffers; D005696:Galactosidases; D001616:beta-Galactosidase; D007785:Lactose