Calcium alginate-immobilized cultures of lactic Streptococci are protected from bacteriophages.

Calcium alginate-immobilized cultures of lactic streptococci were grown in milk and assessed for their sensitivity to homologous bacteriophage, proteolytic activity, and acid production. Immobilized cultures of Streptococcus lactis C2 and Streptococcus cremoris HP were protected from attack by bacteriophage due to the exclusion of phage particles from the gel matrix. These cultures were also functionally proteinase-deficient when immobilized in calcium alginate beads and grown in milk. Acid was produced by immobilized cultures at a lower rate than cells freely suspended in milk due in part to the inability of the immobilized cells to hydrolyze milk proteins. Agitation of immobilized cultures slightly increased acid production, suggesting that diffusional limitations of substrate into the beads contributed to decreased acid production. Use of immobilized cultures of lactic streptococci in certain dairy fermentations may be advantageous due to the protection of these cultures from attack by virulent bacteriophage.