Inhibitory Effects of Microgard^TM on Yogurt and Cottage Cheese Spoilage Organisms

¹ Department of Microbiology
² College of Pharmacy, Oregon State University, Corvallis 97331-3804

Three different concentrations of freeze-dried Microgard^TM were investigated for their inhibitory action against spoilage organisms in two commercial brands of strawberry-flavored yogurt. Evaluation of the Microgard^TM activity in the commercial yogurt samples focused on acid tolerant yeasts and gram-negative bacteria. Yeasts were the principal spoilage organisms contaminating commercial yogurts. Microgard^TM (10% concentration) inhibited viable yeasts and preserved one commercial yogurt brand for over 82 d at 5°C. In the other yogurt brand, yeasts were not eliminated, but their early growth was restricted by 10% Microgard^TM. The inhibitory action of Microgard^TM against yeasts was concentration dependent. The Microgard^TM-supplemented yogurts were also protected from spoilage by gram-negative psychrotrophs which grew out following pH increases as a result of yeast growth.

In the case of commercially produced cottage cheese, a significant reduction in spoilage due to inhibition of gram-negative psychrotrophs by liquid Microgard^TM was observed. In 24 d, 90% (105 out of 114 cartons) of cottage cheese that contained liquid Microgard^TM had less than 800 gram-negative bacteria/g of cottage cheese. In 30 d, 68% (78 out of 114 cartons) of the cottage cheese had undetectable levels of spoilage organisms (less than 100/g) when the cottage cheese was kept at 7°C. Less than 1% of cottage cheese that contained liquid Microgard^TM showed any surface growth (mold) and 33% of the cottage cheese that did not contain liquid Microgard^TM underwent surface spoilage in 21 d.

Key Words: spoilage organisms • cottage cheese • yogurt

Submitted on October 27, 1988
Accepted on October 16, 1989