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Factors Influencing Growth and Toxin Production in Cheese Inoculated with Spores of Clostridium Botulinum Types A and B. II. Studies with Surface-Ripened Cheese Type II¹

Food Research Institute, The University of Chicago, Chicago, Illinois

ABSTRACT

Studies were conducted to determine the maximum brine concentrations Clostridium botulinum Types A and B would tolerate before ceasing growth and toxin production in heated surface mold-ripened cheese designated Type II. Data from four series of experiments are presented. In the three groups of trials involving this cheese with initial pH levels above 5.7, the maximum brine concentrations at which toxin was produced varied widely. Growth and toxin production by the three strains of C. botulinum Type A tested was better in cheese without stabilizer than with stabilizer added. In two comparable groups with stabilizer, the maximum brine concentrations associated with growth and toxin production by both Type A and Type B C. botulinum were higher in the adjusted pH cheese preparations than in those at their normal pH level. Type II cheese with added stabilizer and initial pH levels of 5.7 or below was a poorer medium than similar preparations with pH levels above 5.7, but was an equally good medium for growth and toxin production of C. botulinum when the pH was adjusted upward with NaOH solution. Growth and toxin production occurred in cheese with brine concentrations up to more than 7.0% when Type A spores were used; with Type B spores, the maximum brine concentrations tolerated were near 6.0%.

¹ These studies were supported by a grant from the National Cheese Institute.

² Present address: Central Research Laboratories, General Mills, Inc., Minneapolis 13, Minnesota.