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Title: INFLUENCE OF STREPTOCOCCUS THERMOPHILUS MR-1C CAPSULAR EXOPOLYSACCHARIDE ON CHEESE MOISTURE LEVEL

Author
item LOW, DEBORAH - UTAH STATE UNIVERSITY
item Ahlgren, Jeffrey
item HORNE, DIANE - WEBER STATE UNIVERSITY
item MCMAHON, DONALD - UTAH STATE UNIVERSITY
item OBERG, CRAIG - WEBER STATE UNIVERSITY
item BROADBENT, JEFFERY - UTAH STATE UNIVERSITY

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: The level of moisture in dairy products such as cheese can dramatically affect their physical attributes, particularly texture and strength. The moisture level is critical for consumer acceptance in recently developed low-fat versions of cheeses, as too little moisture results in a brittle, crumbly product, whereas too much can cause it to become gummy. Moisture levels and moisture retention properties can be engineered into a cheese through the appropriate use of additives. Some additives such as complex carbohydrates occur naturally during the culturing of the cheese with food grade microorganisms. This study demonstrated that a complex carbohydrate made by a bacterium used during the culturing of a low fat Mozzarella cheese improves the retention of water; this was shown by genetically altering the bacterium so that it did not make the complex carbohydrate. This study also determined the composition of the complex carbohydrate made by the bacterium; in this particular case, their was one feature about it that has not been previously seen in other bacteria used to culture cheese. These results will be primarily of interest to cheese producers who are trying to improve the overall quality of low-fat cheese.

Technical Abstract: The objective of this study was to investigate the role of exopolysaccharide in cheese moisture retention. Analysis of low-fat Mozzarella cheese made with different combinations of exopolysaccharide-producing (Streptococcus thermophilus MR-1C and Lactobacillus delbrueckii ssp. bulgaricus MR-1R) and non- exopolysaccharide-producing (S. thermophilus TA061 and Lactobacillus helveticus LH100) starter cultures showed significantly higher moisture levels in cheese made with S. thermophilus MR-1C. To determine if S. thermophilus MR-1C exopolysaccharide was responsible for the increased moisture retention, a gene replacement approach was used to inactivate the epsE gene in this bacterium. Low-fat Mozzarella cheese made with L. helveticus LH100 plus the exopolysaccharide-negative mutant, S. thermophilus DM10, had significantly lower moisture content than cheese made with LH100 and MR-1C, which confirmed that the MR-1C capsular exopolysaccharide was responsible for the water-binding properties of this bacterium in cheese. Chemical analysis of the S. thermophilus MR-1C exopolysaccharide suggested that it had a basic repeating unit composed of D-galactose, L-rhamnose, and L. fucose in a ratio of 5:2:1. Interestingly, carbohydrate utilization tests showed that S. thermophilus DM10 had acquired the ability to ferment galactose.