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Applied and Environmental Microbiology, July 1999, p. 3261-3263, Vol. 65, No. 7
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Development of Bacterial Contamination during Production of Yeast Extracts

Julie Barrette,1 Claude P. Champagne,2,* and Jacques Goulet1

Département des Sciences des Aliments et de Nutrition, Université Laval, Québec, Québec G1K 7P4,1 and Food Research and Development Center, Agriculture and Agri-Food Canada, St. Hyacinthe, Québec J2S 8E3,2 Canada

Received 21 October 1998/Accepted 23 April 1999

Baker's yeast suspensions having bacterial populations of 106 and 108 CFU/ml were subjected to autolysis processes designed to obtain yeast extracts (YE). The bacterial contaminants added to the yeast cell suspensions were produced with spent broths obtained from a commercial yeast production plant and contained 59% cocci (Leuconostoc, Aerococcus, Lactococcus) as well as 41% bacilli (Bacillus). Autolyses were conducted at four different pH levels (4.0, 5.5, 7.0, and 8.5) and with two autolysis-promoting agents (ethyl acetate and chitosan). Processing parameters were more important than the initial bacterial population in the development of contaminating bacteria during manufacture of YE. Drops in the viable bacterial population after a 24-h autolysis were observed when pH was adjusted to 4.0 or when ethyl acetate was added. A significant interaction was found between the effects of pH and autolysis promoters on the bacterial population in YE, indicating that the activity of ethyl acetate, as opposed to that of chitosan, was not influenced by pH.

* Corresponding author. Mailing address: Food Research and Development Center, Agriculture and Agri-Food Canada, 3600 Casavant, St. Hyacinthe, Quebec J2S 8E3, Canada. Phone: (514) 773-1105. Fax: (514) 773-8461. E-mail: CHAMPAGNEC{at}em.agr.ca.

Applied and Environmental Microbiology, July 1999, p. 3261-3263, Vol. 65, No. 7
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.




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Copyright © 1999 by the American Society for Microbiology. All rights reserved.