Potential use of the nisin produced by lactic acid bacteria for longer conservation of camel cheese

Abstract

In fermented foods, lactic acid bacteria (LAB) display numerous antimicrobial activities. This is mainly due to the production of organic acids, but also of other compounds, such as bacteriocins and antifungal peptides. Several bacteriocins with industrial potential have been purified and characterized. This study aims to highlight on the antagonistic effect of lactic strain producer of bacteriocin (Lactococcus lactis ssp. Lactis) against a psychrotrophic strain (Pseudomonas fluorescens) contaminating the milk stored in the cold. The strain producing lactic bacteriocins (nisin-type) is isolated from a fresh camel cheese prepared in the laboratory with a significant yield, equal to 35.5%. The indicator strain is a psychrotrophic strain isolated from a sample of raw camel milk, stored at 4°C for more than three days. Thus, the neutralized supernatant of a culture of Lactococcus lactis ssp. Lactis in M17 medium (8000 g/20 min at 4°C) was tested against the strain of Pseudomonas fluorescens by the three techniques of gel diffusion; spots, wells and disks. The neutralized supernatant showed antibacterial activity which was manifested by the appearance of inhibition zones where diameter differs depending on the test used. Diameters varying between 9 and 18 mm and between 12 and 29 mm were recorded respectively with wells and disks. The technique of spots has been less conclusive.