Reliability of coliform as an indicator for post processing contamination in yoghurt manufacture.

摘要

Reliability of coliform bacteria as an indicator of post-processing contamination of yoghurt was investigated. Escherichia coli isolated from commercial yoghurt were inoculated into Tryptone Soya Broth (TSB) and sterilized milk (SM) with an initialpH of 3.5, 4.0, 4.5 and 5.0. Growth was monitored after 0, 24 and 48 h incubation at 37鳦 by measuring changes in optical density (OD) and pH in the TSB and pH in SM. For comparison, Enterococcus faecium [Streptococcus faecium] was also inoculated. Heatresistance of both bacteria was determined at 63, 75, 80 and 90鳦 for 30 min, 15 s, 10 min and 5 min respectively. Experimental yoghurt was inoculated at 2 levels (102 and 105 c.f.u./ml) of coliform bacteria or enterococci, and their fate was monitored daily for up to 15 days of storage at refrigeration temperature. Results indicated improved reliability of coliform bacteria compared with enterococci as an indicator of post-processing contamination in yoghurt. Coliform bacteria could withstand lower pHin TSB, SM and yoghurt for longer times than enterococci.