Investigate the microbial safety of process cheeses.

Scientists at the University of Wisconsin (Food Research Institute, 1925 Willow Dr., Madison, WI 53706) have attempted to determine whether the safety of process cheese is affected by the type of natural cheese from which it is derived. As part of their investigation, the researchers evaluated the effect of fat and fat replacers on the growth of C. botulinum in full-fat, reduced-fat and fat-free process cheese products.

The investigators determined the efficacy of antimicrobials in these products. They identified the factors that inhibit botulinal toxin production in the products and evaluated the effect of moisture-fat-free and nonfat solids in process cheese products made with skim milk cheese, disodium phosphate, sodium chloride and water.

Process cheese and related foods and spreads account for more than 2 billion lb of dairy products in the United States. Traditionally, the microbiological safety of these products relies on formulations that inhibit toxin production by C. botulinum. In order to produce organoleptically acceptable reduced-fat and fat-free products, microbial controls, such as moisture, salt, and pH, are often adjusted to more permissive conditions. This raises safety concerns among the dairy industry and regulators.

Preliminary research at the university suggests that C. botulinum toxin production is delayed in reduced-fat and fat-free process cheese products, compared with full-fat products with similar levels of moisture, salt and pH. However, the mechanism of inhibition is unknown.

In tests, process cheese spreads were manufactured with natural cheese that contained either full-fat cheddar cheese, reduced-fat cheddar or skim milk cheese. The cheese spreads were supplemented with ingredients to conform with the U.S. Federal Standard of Identity for pasteurized process cheese spreads. The formulations were adjusted to 59% moisture, pH 5.8, and 3% or 4% total salts. Researchers selected these formulations to permit growth and toxin production by C. botulinum. In this way, differences in inhibition of growth and toxin production could be evaluated and statistically analyzed.

Botulinal toxin was delayed two days in skim milk process cheese formulated with 4% salts. Additionally, there were fewer toxic samples for process cheese made with skim milk cheese than for formulations manufactured with reduced-fat or full-fat cheese. Investigators believe that moisture was not a valid indicator of safety in 5% fat and fat-free process cheese products. These products appeared to exhibit greater stability than full-fat products with similar moisture, pH and salts.

A more useful parameter for predicting safety may involve a moisture-fat-free (MFF) approach that compensates for the different fat levels. Investigators evaluated the effect of MFF in process cheese products manufactured with skim milk cheese, disodium phosphate, sodium chloride and water. All products were standardized to 2.8% total salts and pH 5.8. Decreasing moisture delayed botulinal growth and toxin production. However, these formulations supported toxin production more rapidly than previous fat-free trials formulated with added process-cheese ingredients (whey products, fat replacers, flavor adjuncts, enzyme modified cheese and the like). This suggests the safety of reduced-fat process cheese products may rely on other parameters or the interaction of several ingredients.

Further information. Eric Johnson; phone: [phone]; fax: [phone]; URL: http://www.cdr.wisc.edu.