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Appl Environ Microbiol, June 1998, p. 2147-2151, Vol. 64, No. 6
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Role of Streptococcus thermophilus MR-1C Capsular Exopolysaccharide in Cheese Moisture Retentiondagger

Deborah Low,1 Jeffrey A. Ahlgren,2 Diane Horne,3 Donald J. McMahon,1 Craig J. Oberg,3 and Jeffery R. Broadbent1,*

Department of Nutrition and Food Sciences, Utah State University, Logan, Utah 84322-87001; Biopolymer Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, Peoria, Illinois 616042; and Department of Microbiology, Weber State University, Ogden, Utah 84408-25063

Received 18 November 1997/Accepted 21 March 1998

Recent work by our group has shown that an exopolysaccharide (EPS)-producing starter pair, Streptococcus thermophilus MR-1C and Lactobacillus delbrueckii subsp. bulgaricus MR-1R, can significantly increase moisture retention in low-fat mozzarella (D. B. Perry, D. J. McMahon, and C. J. Oberg, J. Dairy Sci. 80:799-805, 1997). The objectives of this study were to determine whether MR-1C, MR-1R, or both of these strains are required for enhanced moisture retention and to establish the role of EPS in this phenomenon. Analysis of low-fat mozzarella made with different combinations of MR-1C, MR-1R, and the non-EPS-producing starter culture strains S. thermophilus TA061 and Lactobacillus helveticus LH100 showed that S. thermophilus MR-1C was responsible for the increased cheese moisture level. To investigate the role of the S. thermophilus MR-1C EPS in cheese moisture retention, the epsE gene in this bacterium was inactivated by gene replacement. Low-fat mozzarella made with L. helveticus LH100 plus the non-EPS-producing mutant S. thermophilus DM10 had a significantly lower moisture content than did cheese made with strains LH100 and MR-1C, which confirmed that the MR-1C capsular EPS was responsible for the water-binding properties of this bacterium in cheese. Chemical analysis of the S. thermophilus MR-1C EPS indicated that the polymer has a novel basic repeating unit composed of D-galactose, L-rhamnose, and L-fucose in a ratio of 5:2:1.

* Corresponding author. Mailing address: Department of Nutrition and Food Sciences, Utah State University College of Agriculture, Logan, UT 84322-8700. Phone: (435) 797-2113. Fax: (435) 797-2379. E-mail: Broadbnt{at}cc.usu.edu.

dagger Journal paper 6079 of the Utah Agricultural Experiment Station, Utah State University.

Appl Environ Microbiol, June 1998, p. 2147-2151, Vol. 64, No. 6
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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