Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/1999
Publication Date: N/A
Citation: Interpretive Summary: New markets are needed for American farm products. In that regard, there are a number of fermented milk products such as yogurt available to consumers today. These products get their properties from the chemical changes caused by the particular microorganism used. By studying the chemical events that are occurring, it will be possible to manipulate the fermentation of milk in new and desirable ways. This report describes some of the properties of a bacterium that produces fermented milk with the consistency of a pourable yogurt, which is desirable to some consumers. The bacterium produces a particular type of complex carbohydrate known as a polysaccharide; in this case, two polysaccharides which were independently isolated and studied. This study examined the chemical nature of these polysaccharides and showed that they were different from any previously described. It was also shown that only one was responsible for changing the milk to a thickened solution. The work is of interest to farmers, the dairy agribusiness, and consumers, as well as other scientists.
Technical Abstract: A natural lactococcal isolate, Lactococcus lactis ssp. cremoris Ropy352, has been previously shown to express two phenotypically distinct exopolysaccharides (ropy and mucoid). This natural isolate was cultured on various media to explore the carbon requirements for exopolysaccharide expression. Ropy exopolysaccharide expression was optimal when grown in defined media rather than on M17-based media. Ropy 352 was examined for inducible lysogenic phages. No lytic burst was observed in Ropy352 using either ultraviolet light or mitomycin C for phage induction. The sugar compositions of the two phenotypically distinct exopolysaccharides were determined. The ropy exopolysaccharide is composed of glucose and galactose in the molar percents of 58% and 45%, respectively. The mucoidy exopolysaccharide is composed of galactose, glucose, and mannose in the molar percents of 58%, 29%, and 13%, respectively. Mutational analysis revealed that mutations impairing ropy exopolysaccharide expression but not affecting mucoid exopolysaccharide expression could be isolated.