Many strains of Streptococcus thermophilus synthesize extracellular polysaccharides. These molecules may be produced as capsules that are tightly associated with the cell, or they may be liberated into the medium as a loose slime (i.e., "ropy" polysaccharide). Although the presence of exopolysaccharide does not confer any obvious advantage to growth or survival of S. thermophilus in milk, in situ production by this species or other dairy lactic acid bacteria typically imparts a desirable "ropy" or viscous texture to fermented milk products. Recent work has also shown that exopolysaccharide-producing S. thermophilus can enhance the functional properties of Mozzarella cheese, but they are not phage-proof. As our understanding of the genetics, physiology, and functionality of bacterial exopolysaccharides continues to improve, novel applications for polysaccharides and polysaccharide-producing cultures are likely to emerge inside and outside the dairy industry. This article provides an overview of biochemistry, genetics, and applications of exopolysaccharide production in S. thermophilus.

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We investigated the effect of capsular and ropy exopolysaccharide-producing Streptococcus thermophilus starter bacteria on Mozzarella cheese functionality and whey viscosity. Mozzarella cheeses were manufactured with Lactobacillus helveticus LH100 paired with one of four S. thermophilus strains: MR-1C, a bacterium that produces a capsular exopolysaccharide; MTC360, a strain that secretes a ropy exopolysaccharide; TAO61, a nonexopolysaccharide-producing commercial cheese starter; and DM10, a nonencapsulated, exopolysaccharide-negative mutant of strain MR-1C. As expected, cheese moisture levels were significantly higher in Mozzarella cheeses made with exopolysaccharide-positive versus exopolysaccharide-negative streptococci, and melt properties were better in the higher moisture cheeses. Whey viscosity measurements showed that unconcentrated and ultrafiltered, fivefold concentrated whey from cheeses made with S. thermophilus MTC360 were significantly more viscous than whey from cheeses made with MR-1C, TAO61, or DM10. No significant differences were noted between the viscosity of unconcentrated or concentrated whey from cheeses made with S. thermophilus MR-1C versus the industrial cheese starter TAO61. These data indicate that encapsulated, but not ropy, exopolysaccharide-producing S. thermophilus strains can be utilized to increase the moisture level of cheese and to improve the melt properties of Mozzarella cheese without adversely affecting whey viscosity.

Ninety-one essential oils, each distilled from a single plant source, and 64 blended essential oils obtained from a commercial source were screened using the disc diffusion assay for inhibitory activity against methicillin-resistant Staphylococcus aureus (MRSA). Of the 91 single essential oils, 78 exhibited zones of inhibition against MRSA, with lemongrass, lemon myrtle, mountain savory, cinnamon and melissa essential oils having the highest levels of inhibition. Of 64 blended essential oils, 52 exhibited inhibitory activity against MRSA, with R.C. (a combination of myrtle, Eucalyptus globulus, Eucalyptus australiana, Eucalyptus radiata, marjoram, pine, cypress, lavender, spruce, peppermint and Eucalyptus citriodora oils), Motivation (a combination of Roman chamomile, ylang ylang, spruce and lavender oils) and Longevity (a combination of frankincense, clove, orange and thyme oils) blended essential oils having the highest inhibitory activity. These results indicate that essential oils alone and in combination can inhibit MRSA in vitro. Application of these results may include the potential use of essential oils as an alternative therapy for various diseases sustained by S. aureus MRSA.