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Factors Affecting Swiss Cheese Starter Activity Effect of Heat-Treatment and Source of Milk

Department of Bacteriology, The Ohio State University

ABSTRACT

1. Heat-treatment of milk from a single source at 80° C. for periods up to 4 hours had little effect on the activity of Swiss cheese starters subsequently inoculated.
   
2. Heat-treatment at 100° C. for 2 to 4 hours increased the rate of acid production by the starters over that occurring in milk heated a shorter or a longer period. Similar stimulation was observed in milk heated at 120° C. for 30 to 45 minutes.
   
3. The redox potential of the milk samples showed a downward trend with increase in temperature or with the longer holding periods at any one temperature.
   
4. The increased rate of acid production in milk heated at 100° C. for 2 to 4 hours appeared to be due to an increased growth rate, since the fermenting capacity of the cells decreased progressively in milk heated for the longer periods.
   
5. The composition of the milk, as determined by source, had a greater effect on the activity of the starters than heat-treatment.
   
6. It is suggested that important differences in the activity of Swiss cheese starters may be due to variations in (1) the oxidation-reduction potential in milk and (2) the growth factor content of milk from different sources.
   

¹ Now of the Dept. of Path, and Bact., Colorado State College, Ft. Collins.