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Effects of Copper on Microorganisms in the Manufacture of Swiss Cheese^{1 ,2,}

Department of Food Technology, Iowa State University, Ames 50010

ABSTRACT

Commercial strains of Lactobacillus bulgaricus, Streptococcus thermophilus, lactic streptococci, and propionibacteria were grown in the presence of 0, 2, 4, 8, and 16 ppm copper to simulate conditions that might exist in Swiss cheese manufacture. In general, loss of viability and inhibition of acid production was hastened by an increase in copper concentration although genus, species, and strains differed. During the first 3 h of incubation in milk, mixed-strain lactic cultures were not affected by the addition of copper up to 16 ppm. Later, inhibition and increased death rates occurred depending upon copper concentration. S. thermophilus strains exhibited a wide variety of sensitivities to copper. However, they seemed to overcome partly their sensitivity to copper after about 16 h incubation. Two of three strains of L. bulgaricus showed slight reduction in cell numbers and acid production with increasing copper concentration. The third strain more closely resembled the lactic streptococci in its greater sensitivity to copper. Two of four strains of propionibacteria were more sensitive to copper than were the other two. Carbon dioxide production in broth at pH 7.0 differed among the strains. Incubation periods up to 20 days, however, tended to overcome copper inhibition. At an initial broth pH of 5.4, carbon dioxide production was delayed markedly by 16 ppm copper, but, with prolonged incubation, two of the four strains attained carbon dioxide production equal to copper-free controls.

¹ Journal Paper No. J-8015 of the Iowa Agriculture and Home Economics Experiment Station, Ames 50010. Project No. 1839.

² Supported in part by a grant from the Kraftco Corp., Research and Development Division, 801 Waukegan Road, Glenview, IL 60025.

³ Institut f. Milchwirtschaft u. Mikrobiologie, Hochschule f. Bodenkultur, Gregor Mendenstr. 33, A-1180 Vienna, Austria.

⁴ Research and Development, Leprino Cheese Company, P. O. Box 8400, Denver, CO 80201.