PRODUCTION OF A BACTERIOCIN ACTIVE ON LACTATE-FERMENTING CLOSTRIDIA BY LACTOCOCCUS-LACTIS SUBSP LACTIS IMMOBILIZED IN COATED ALGINATE BEADS

We report the isolation and immobilization of a nisinogenic strain (NZ 1) of Lactococcus lactis subsp. lactis, active on gas-forming lactate- fermenting clostridia responsible for late blowing of Asiago and Monta sio cheeses. The bacteriocin (nisin) produced by strain NZ1 is pronase -sensitive and is released in culture media during the growth phase. U sing the sensitive indicator strain Lactobacillus delbrueckii subsp. b ulgaricus NCDO 1489, a rapid microtitre plate based assay was develope d for quantitative determination of the bacteriocin produced by NZ1 ce lls, either free or immobilized in gel beads. Scanning electron micros copy of cells immobilized in calcium alginate coated beads and viable counts of the surrounding medium showed that no cell leakage occurred during a 24 h assay. The bacteriocin released from immobilized cells r eached, after 5 and 24 h, concentrations comparable to that of the fre e cell system after 3-4 h incubation in culture media.