Evaluation of recovery media for heated spores of Bacillus stearothermophilus

Abstract

The effects of different media, additives, pH and incubation temperatures were studied on the recovery of heat‐treated spores of Bacillus stearothermophilus. Raising the pH from 6.5 to 7.3 increased the shoulder and decreased the subsequent exponential rate of inactivation with some of the media. Addition of starch or charcoal caused a significant increase in the level of recovery. No significant differences were observed by using two incubation temperatures (50° or 60°C). Yeast‐peptone‐tryptone‐dextrose medium plus starch was found to be the best of the media used.

Heat resistance of Bacillus cereus spores in carrot extract acidified with different acidulants

“…This sensitivity to acid environments is one of the main signs of thermal injury (Blocher & Busta, 1983;Ló pez et al, 1997;Silla, 1993). The results obtained in the present study when spores were recovered in NA + C and A + C confirm and complement evidence for the existence of an interaction between the composition and the pH of the subculture medium, as was previously pointed out for B. cereus (González et al, 1996) and B. stearothermophilus (Mallidis & Scholefield, 1986;Yokoya & York, 1965). These findings reveal that subsequent effects of the surround- ing environment must also be considered in order to establish a suitable heat treatment.…”

Modelling the overall effect of pH on the apparent heat resistance of Bacillus cereus spores

“…At non optimum recovery conditions, both a decrease in the number of viable cells capable of producing colonies and a decrease in the estimated decimal reduction time are observed. It is generally accepted that the pH of the recovery medium exerts a great influence on the apparent heat resistance of spores: D-values decrease as pH is reduced (Cook and Brown, 1965;Yokoya and York, 1965;Cook and Gilbert, 1968;Mallidis and Scholefield, 1986;Santos and Zarzo, 1996;Lopez et al, 1997). This paper aims to present a simple overall model which takes into account both the effect of the pH of the heating menstruum and that of the recovery medium upon the observed D-value.…”

Influence of recovery conditions on apparent heat resistance of Bacillus stearothermophilus spores

“…The dependence of heat inactivation parameters upon the recovery medium has been less studied. Some authors have reported that International Journal of Food Science and Technology 1997, 32, 305-311 D-values are dependent on the recovery media (Campbell et al, 1965;Yokoya & York, 1965), while others (Cook & Gilbert, 1968;Labbe, 1979;Mallidis & Scholefield, 1986) have pointed out that the differences observed in D-values are only caused by the presence of some substances such as starch, charcoal or NaCl. As far as we know, there is no available information on the effect of recovery medium on z-value, although Zechman & Pflug (1991) suggested that z-value should be larger when using media of reduced concentration, but they have not confirmed this experimentally.…”