G. F. De Valdez

Proteolytic activity and reduction of gliadin-like fractions by sourdough lactobacilli

Aims:  To characterize the peptide hydrolase system of Lactobacillus plantarum CRL 759 and CRL 778 and evaluate their proteolytic activity in reducing gliadin‐like fractions.

Bile salts hydrolase plays a key role on cholesterol removal by Lactobacillus reuteri

The [ H]cholesterol removal by Lactobacillus reuteri was due to a co-precipitation together with unconjugated bile acids, which was linked to the bile salt hydrolase activity of the cells. No [ H]cholesterol was found inside the cells indicating that no assimilation occurred.

Adaptive acid tolerance response in Lactobacillus acidophilus

Stationary phase cultures of Lactobacillus acidophilus CRL 639 are naturally acid resistant to pH 3.0 while exponential phase cells induce an acid tolerance response upon exposure to sublethal pH (3.8–6.0). Maximal response was achieved after adaptation at pH 4.2 and pH 5.0. Protein synthesis was required in the latter case.

Effectiveness of Soy Milk as Food Carrier for Lactobacillus Acidophilus

: Three mild-fermented milk beverages prepared from soy milk and cows milk were compared for their ability to preserve the cell viability of Lactobacillus acidophilus during refrigerated storage, in associative growth with Lactobacilus casei and Streptococcus thermophilus . The highest survival rate was obtained by using soy milk as substrate. The presence of L. casei in the starter culture had no influence on the viability of L. acidophilus , while the streptococcal cells showed a harmful effect. The culture activity measured as proteolysis and acid production remained fairly constant during the shelf life, despite the variations in colony counts observed for the different fermented milks analyzed.

Temperature adaptation and cryotolerance in Lactobacillus acidophilus

The response of Lactobacillus acidophilus CRL 639 to cold-shock (freezing) depends on the initial growth temperature. Cells cultured at 25°C (long filaments with a μ value of 0.02 h−1) show a higher β-galactosidase activity and develop cryotolerance, compared with cells grown at 37°C. One-dimensional proteins gel electrophoresis shows the over-expression of six proteins (22.5–105.0 kDa) and the repression of eight proteins (4.3–48.0 kDa) at 25°C.

Shifts in pH affect the maltose/glycerol co-fermentation by Lactobacillus reuteri

In aerated cultures of Lactobacillus reuteri using maltose/glycerol, lactate was the main product followed by acetate at all pH (4.7, 5.5 and 6.5) tested while anaerobic cultures produced 1,3-propanediol besides lactate, acetate and ethanol. 1,3-Propanediol was the main product at pH 5.5 and 6.5. The high amount of acetate and the low concentration of ethanol found in anaerobic cultures was closely related to the synthesis of 1,3-propanediol.

L-glutamate transport in Lactobacillus helveticus

An energy source (glucose or lactose) was required for the transport of L-glutamic acid by Lactobacillus helveticus. Mg(2+), K(+) and Li(+) increased its accumulation while Ca(2+) and Na(+) decreased it. It was inhibited by NaF, indicating that ATP may be involved in uptake. Optimum transport was at pH 7.3 and 45°C. L-Glutamic acid transport showed a high degree of stereospecificity, as neither D-glutamate nor D-aspartate were active. Proton-conducting uncouplers, like carbonyl cyanide-m-chlorophenylhydrazone, and ionophores (nigericin, monensin and gramicidin) were strongly inhibitory. These results indicate that a proton motive force may be involved in the transport of L-glutamic acid.An energy source (glucose or lactose) was required for the transport of l-glutamic acid by Lactobacillus helveticus. Mg2+, K+ and Li+ increased its accumulation while Ca2+ and Na+ decreased it. It was inhibited by NaF, indicating that ATP may be involved in uptake. Optimum transport was at pH 7.3 and 45°C. l-Glutamic acid transport showed a high degree of stereospecificity, as neither d-glutamate nor d-aspartate were active. Proton-conducting uncouplers, like carbonyl cyanide-m-chlorophenylhydrazone, and ionophores (nigericin, monensin and gramicidin) were strongly inhibitory. These results indicate that a proton motive force may be involved in the transport of l-glutamic acid.