Stimulation of Lactic Streptococci in Milk by β-Galactosidase1

Abstract

Acid production in milk by lactic streptococci was stimulated by added j3galactosidase. Both glucose and galactose accumulated rapidly in the presence of this enzyme. Glucose accumulation ceased as the culture entered the most rapid period of acid production, whereas galactose accumulation continued. In cultures without added f3-galactosidase, a low concentration of galactose accumulated in the milk, whereas glucose was not detected after 2 hr of incubation. Cultures grew and produced acid faster in broth containing glucose rather than galactose or lactose. These observations suggest that the lactic streptococci do not metabolize the lactose in milk efficiently enough to permit optimum acid production and that a phenomenon such as catabolite repression functions to allow for a preferential use of glucose over either galactose or lactose. In addition to providing the culture with a more readily available energy source, it is possible that the culture produced more acidic metabolites as a result of preferentially utilizing the glucose released by the action of the f,-galactosidase.

A yoghurt-like product made by fermenting ultrafiltered milk containing elevated whey proteins withLactobacillus acidophilus

“…The finding that addition of lactase to milk stimulated acid production by Str. thermophilus (Gilliland et al 1972) and by a mixed culture of Str. thermophilus and L. bulgaricus (O'Leary & Woychik, 1976) is in accordance with our observations on the growth of L. acidophilus in milk supplemented with lactase.…”

Proteolytic enzymes of dairy starter cultures

“…After enzymatic hydrolysis of whole casein and fractionation of the peptides, it was shown that peptides in the M r range 1-2.5 kDa were the most stimulatory for S. thermophilus [89]. Stimulation of both lactic streptococci and S. thermophilus by adding/3-galactosidase to milk has been reported [90,91]. However, this effect was not due to lactose hydrolysis but rather to contamination of the enzyme by proteinase [92,93].…”

Utilization of Lactose, Glucose, and Galactose by a Mixed Culture of Streptococcus thermophilus and Lactobacillus bulgaricus in Milk Treated with Lactase Enzyme

“…A stimulation of acid production by lactic streptococci in milk cultures upon the addition of ,-galactosidase to hydrolyze the milk lactose to glucose and galactose was reported by Gilli-land et al (4). They (4) suggested that optimum acid production by lactic streptococci does not take place in milk cultures due to an inability of the organisms to metabolize the lactose at maximum efficiency.…”

“…Gilliland et al (4) suggested that increased acid production by lactic streptococci in milk cultures in the presence of f8-galactosidase might be due to conversion of a greater percentage of glucose than lactose to acid end products. We have previously shown (10) that LH yogurts having a pH of 4.6 contained more lactic acid than did control yogurts at the same pH.…”