Antimicrobial Agent of Aged Surface Ripened Cheese.

SUMMARY Antibiotic activity in aged Liederkranz cheese was found to be produced by the aerobic microorganisms inhabiting its surface. Brevibacterium linens was the principal source of the antimicrobial agent(s). Yeast of the Candida type and, when present, some other microorganisms contributed minor antimicrobial activity. The antimicrobial agent(s) of aged Liederkranz cheese had the following properties: 1) dialysable through cellulose casing, 2) absorbed on Norit A at acid pH, 3) stable in acid and alkaline solutions ranging from pH 2.0 to 12.0 at 24° C, 4) destroyed within 20 hr in alkaline solution at pH 12 at room temperature, 5) in aqueous solution stable to heating at 121° C for 10 min at acid pH(pH<5.0) but decreased activity at pH 5.0 to 8.5, 6) in agar medium of pH 6.8–7.0 activity remained after heating at 121° C for 45 min, 7) soluble in water, methanol, ethanol, and butanol, slightly soluble in acetone and insoluble in ethyl ether, carbon tetrachloride, chloroform and ethyl acetate, 8) inhibited growth of many gram‐positive and gram‐negative bacteria as well as several yeasts and molds, and 9) related to antibiotic from B. linens but distinct from nisin, an antibiotic commonly associated with dairy products. In a survey of market samples of cheeses to determine whether antibiotic activity was present, only surface‐ripened cheeses with a brown smear made up of bacteria were found to contain antibacterial activity. Other types of cheeses which did not develop this brown smear did not possess this activity. It may be concluded that antibiotic activity is contained in the brown bacterial surface smear that develops during ripening.