Proteolytic Activity by Strains of Lactobacillus plantarum and Lactobacillus casei

Growth, acid production, and hydrolysis of milk.proteins in sterile skim milk at 37"C were detennined for seven strains of Lactobacillus plantarum, two of Lactobacillus casei, and one of L. casei ssp.pseudoplantarum.Hydrolysis of milk.protein was monitored by SDS-PAGE.Lactobacillus plantarum NRRL B-4004 was the most proteolytic and began to hydrolyze ~-casein after 125 h; hydrolysis was complete after 215 h.All strains of L. plantarum preferentially degraded ~-casein of milk.whereas <Xs1-<:asein was partially hydrolyzed by some strains.Lactobacillus casei NRRL B-1922 and L. casei NRRL-B 441 did not hydrolyze ~ casein even after 265 h.Lactobacillus casei ssp.pseudoplantarum ATCC 25598 partially hydrolyzed ~-<:asein after 215 h.The pH of milk.at the end of proteolysis was above 4.0 with L. plantarum, 3.7 to 3.8 with L. casei, and 4.1 with L. casei ssp.pseudoplantarum ATCC 25598.Four strains of L. plantarum had maximum viable cell populations ranging from 1.2x 1()6 to 2.0 x 1()6 cfu/rnl.Two strains of L. plantarum exhibited minimal growth, whereas the viable cell population of the two strains of L. casei varied markedly.The viable cell population of L. casei ssp.pseudoplantarum at the end of proteolysis was similar to that of L. plantarum at 2.0 x I()6 cfu/rnl.