Inhibition ofEscherichia coliO157:H7 in commercial and traditional fermented goat milk by activated lactoperoxidase

Abstract

The lactoperoxidase (LP) system has been reported to inhibit the production of acid by lactic starter cultures and can result in the survival and growth of acid-adapted enteropathogens in LP-activated fermented milk. The aim of this study was to investigate the effect of the LP system on growth and acid production by single strains and indigenous lactic acid bacteria (LAB) and the survival of Escherichia coli O157:H7 in fermented goat’s milk. LP-activated raw and pasteurized goat’s milks were inoculated with single strains of Lactococcus sp. and Bifidobacterium longum BB536 and incubated for 24 h at 30 °C to simulate commercial milk fermentation. Madila, a traditional fermented milk product, was fermented with indigenous LAB for 5 days at 30 °C. Goat’s milk was also inoculated with E. coli O157:H7 to determine its survival during the fermentation of the LP-activated milk. The viability of LAB and E. coli O157:H7, pH and acid production were monitored during the fermentations. None of the LAB cultures tested displayed significant sensitivity to the LP system with respect to growth and acid production. However, E. coli O157:H7 was inhibited in the LP-activated milk in the commercial fermented milk and in the traditional Madila, where the counts were reduced by > 5.0 log cfu·mL−1. Therefore, the LP system could be used during the fermentation of both traditional and commercial milk processing at ambient temperatures as an additional bacteriological control to improve the quality of commercial sour milk and traditional Madila-type products.