Pink discoloration of mozzarella cheese

Abstract

The present study was conducted for a dairy manufacturer wishing to find out what was causing pink discoloration in some of their shredded cheese. The probable causes of the defect such as ingredients, packaging, storage temperatures, contaminating bacteria, and starter cultures were researched. It was determined that the root of the problem probably lay in the oxidative metabolism of certain starter cultures. A rapid screening test, which was developed in the 1960's by University of Wisconsin - Madison, was used to determine the tendency of currently used culture strains to produce a color reaction in the test media. Thirty-seven mixed cultures of high-temperature streptococci and lactobacilli from 7 plants were studied to determine if the rod or cocci starter culture could be the cause of pink discoloration. When all tests were completed, 2 of the 7 plants had shown positive results. These results were not consistent in all trials. This questions the validity of using the Rapid Screening Test to select cultures for use in the production of mozzarella cheese. Ten single strain cultures found in mixed combinations, which had caused positive results were purchased for further testing. Three rod cultures from a plant producing negative results in Phase I testing were used. A control test was done using no cultures. All of the cultures showed varied results. All but two had at least one positive trial. The results of phase II testing were not significant, but do suggest that there is the possibility that all rod cultures may have the characteristic defect to some degree. It is possible that the results of the test may be an indicator to the degree of severity of the defect, however, this was not proven in this project. Another possibility is that the higher the rod/coccus ratio, the higher the chance that the discoloration will occur. As the shelf life of Mozzarella cheese continues to lengthen through scientific advances, pink discoloration may because an economic problem for cheese manufacturers. Starter culture manufacturers will need to provide their customers with product that will minimize this defect.