Survival of Bacillus cereus vegetative cells during Spanish-style fermentation of conservolea green olives.

The aim of this research was to investigate the survival of artificially inoculated Bacillus cereus during Spanish-style green olive fermentation. Olives were initially treated with lye and subjected to different fermentation procedures including (i) heat shock (85 degrees C for 10 min) and inoculation with Lactobacillus plantarum ACA-DC 287, (ii) heat shock and inoculation with L. plantarum ACA-DC 146, (iii) heat shock and inoculation with Lactobacillus pentosus isolated during previous studies, and (iv) fermentation by indigenous flora (control process). Microbial growth and survival, pH, titratable acidity, and organic acid evolution were monitored. Inactivation of B. cereus was observed during all processes. The pathogen population declined during all fermentations, but a tailing effect was observed in the brines when the population reached 2 log CFU/ml, at which point the pathogen does not pose a risk to human health. The rate of inactivation was higher in heat-shocked inoculated olives (mean of -2.21 log CFU/day) compared with control olives (-1.26 log/day), indicating an advantage of heat shock and inoculation over spontaneous fermentation. The production of organic acids (primarily lactic acid) during fermentation seemed to be the main factor that determined the behavior of the pathogen under stress conditions prevailing in the brine. Principal components analysis was useful for distinguishing among the different fermentation processes on the basis of the relevant organic acid profile.