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Inhibition of Certain Types of Bacterial Spoilage in Creamed Cottage Cheese by the Use of a Creaming Mixture Prepared with Streptococcus citrovorus¹

Dairy Department, Purdue University, Lafayette, Indiana

ABSTRACT

A special creaming mixture consisting of 1.5 parts of cream containing 20% fat and 1.0 part of an acidified culture of Streptococcus citrovorus (Leuconostoc citrovorum), by weight, prevented slime formation on creamed cottage cheese inoculated with Pseudomonas fragi or Pseudomonas putrefaciens. The biacetyl content of regularly creamed cottage cheese was decreased by P. fragi and P. putrefaciens, but these organisms did not decrease the biacetyl content of the specially creamed cottage cheese. Coliform organisms also were inhibited in cottage cheese creamed with the special creaming mixture, but Geotrichum candidum and Candida pseudotropicalis were not inhibited.

The addition of acetic or propionic acid to creamed cottage cheese delayed the formation of slime by P. fragi, and the delay was related to the amount of acid added. However, relatively large amounts of acetic or propionic acid did not entirely eliminate slime formation and the addition of these acids was not as effective as the special creaming mixture. Therefore, the volatile acids formed by S. citrovorus in the special creaming mixture are not considered to be the cause of inhibition of P. fragi.

Cottage cheese creamed with the special creaming mixture always had a slightly lower pH than cheese creamed with a regular creaming mixture. Adjusting the pH of the regular creaming mixture to the same pH as the special creaming mixture (pH 5.2) did not delay the rate of slime formation by P. fragi. Therefore, some factor other than the pH was responsible for the inhibition.

¹ Published with the approval of the Director of the Purdue Agricultural Experiment Station as Journal Series Paper No. 1461.

² Portion of a thesis prepared by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Present address: Breakstone Foods, Inc., Division of National Dairy Products Corporation, Walton, New York.