Role of Streptococcus thermophilus MR-1C capsular exopolysaccharide in cheese moisture retention.
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.
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Department of Nutrition and Food Sciences, Utah State University, Logan, Utah 84322-8700, USA.
Ahlgren
J A
JA
Horne
D
D
McMahon
D J
DJ
Oberg
C J
CJ
Broadbent
J R
JR
D001483:Base Sequence; D002240:Carbohydrate Sequence; D002611:Cheese / Q000382:microbiology*; D017931:DNA Primers / Q000235:genetics; D005524:Food Technology; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D005810:Multigene Family; D010957:Plasmids / Q000235:genetics; D011135:Polysaccharides, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013291:Streptococcus / Q000235:genetics / Q000378:metabolism*
D017931:DNA Primers; D011135:Polysaccharides, Bacterial