Lactobacilli — Their Enzymes and Role in Ripening and Spoilage of Cheese: A Review

Lactobacilli commonly occur in natural cheese because they are used as a starter culture (e.g., Swiss cheese) or enter milk and, thus, cheese as postpasteurization (or heat treatment) contaminants (e.g., Cheddar cheese). Cell-wall-bound, intracellular, and extracellular proteinases occur in lactobacilli; those from some species of Lactobacillus preferentially hydrolyze αs1-casein, whereas those from others prefer β-casein. Peptides released from casein by proteinases are subsequently hydrolyzed by peptidases inside cells of lactobacilli. The intracellular peptidases are a vital part of the mechanism by which lactobacilli make free amino acids that are precursors of some cheese flavor compounds. Aminopeptidase, dipeptidase, carboxypeptidase, and endopeptidase activities have been associated with lactobacilli. Although largely intracellular, membrane-associated peptidases have been noted. Intracellular lipases and esterases also occur in lactobacilli, but activity of these enzymes has been designated as “weak”. Despite this, they probably contribute to flavor development in some varieties of cheese. Certain lactobacilli can cause defects such as formation of white crystals of calcium lactate on the surface of cheese or of biologically active amines that sometimes can cause illness in consumers.