Proteolysis and flavor development were monitored in Cheddar cheese made from milk inoculated with Lactobacillus casei ssp. casei IFPL 731 (104 cfu/mL cheesemilk) or Propionibacterium shermanii NCDO 853 at three different levels (105, 106, and 107 cfu/mL cheesemilk). The pH and chemical composition of the experimental cheeses were not affected by the addition of L. casei or Prop. shermanii. Cheeses inoculated with L. casei or Prop. shermanii at low and medium levels received the best scores for flavor development and body. However, the addition of Prop. shermanii at a high level caused a sweet and nutty flavor. Urea-PAGE, WSN, and RP-HPLC showed minor differences in proteolysis between the control and experimental cheeses. Major differences were found at the amino acid level. In general, the content of amino acid increased as the Propionibacterium inoculum increased in the experimental cheeses. Besides, a decrease in the content of hydrophobic peptides was observed in cheeses inoculated with Prop. shermanii at medium and high levels. The increase in amino acid content was not apparent when L. casei was added to cheese, possibly due to the lack of cell lysis. There is an optimum inoculum level of Prop. shermanii above which the flavor of Cheddar cheese resembles that of Swiss-type cheese.

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