Detection, growth, and amine-producing capacity of lactobacilli in cheese

A differential plating medium was developed to detect decarboxylating lactobacilli in cheese. With this medium, 15 cheeses made from raw milk were investigated for the presence of these bacteria. Five histidine-decarboxylating strains and one tyrosine-decarboxylating strain were isolated. The isolates were identified with the API 50L system. Accordingly, each of the five histidine-decarboxylating strains was identified as Lactobacillus buchneri, whereas the tyrosine-decarboxylating strain is a representative of Lactobacillus brevis. Cheesemaking experiments using a low inoculum concentration of the histidinedecarboxylating L. buchneri strain St2A (0.2 CFU/ml of milk) showed that, under conditions of accelerated proteolysis, histamine may accumulate rapidly; after 3 months of ripening, 410 mg/kg was found. An inoculum concentration of 5 CFU/ml gave rise to the formation of 1,060 mg/kg.