Factors affecting capsule size and production by lactic acid bacteria usedas dairy starter cultures

The effects of sugar substrates on capsule size and production by some caps ule-forming nonropy and ropy dairy starter cultures were studied. Test suga rs (glucose, lactose, galactose, or sucrose) were used as a sole carbohydra te source and the presence of a capsule and its size were determined by usi ng confocal scanning laser microscopy. Nonropy strains produced maximum cap sule size when grown in milk. Strains that did not produce capsules in mill i did not produce them in any other growth medium. Specific sugars required for capsule production were strain-dependent. Increasing lactose content o f Elliker broth from 0.5 to 5% or adding whey protein or casein digest prod uced larger capsules. Whey protein concentrate stimulated production of lar ger capsules than did casamino acids or casitone. Some Streptococcus thermo philus strains produced capsules when grown on galactose only. Nonropy stra ins of Lactobacillus delbrueckii subsp. bulgaricus produced capsules on lac tose, but not on glucose. A ropy strain of Lactobacillus delbrueckii subsp, bulgaricus produced a constant capsule size regardless of the growth mediu m. The ability of some strains of Streptococcus thermophilus to use galacto se in capsule production could reduce browning of mozzarella cheese during baking by removing a source of reducing sugar. Media that do not support ca psule production may improve cell harvesting. (C) 2001 Elsevier Science B.V . All rights reserved.