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

The effects of sugar substrates on capsule size and production by some capsule-forming nonropy and ropy dairy starter cultures were studied. Test sugars (glucose, lactose, galactose, or sucrose) were used as a sole carbohydrate source and the presence of a capsule and its size were determined by using confocal scanning laser microscopy. Nonropy strains produced maximum capsule size when grown in milk. Strains that did not produce capsules in milk did not produce them in any other growth medium. Specific sugars required for capsule production were strain-dependent. Increasing lactose content of Elliker broth from 0.5 to 5% or adding whey protein or casein digest produced larger capsules. Whey protein concentrate stimulated production of larger capsules than did casamino acids or casitone. Some Streptococcus thermophilus strains produced capsules when grown on galactose only. Nonropy strains of Lactobacillus delbrueckii subsp. bulgaricus produced capsules on lactose, but not on glucose. A ropy strain of Lactobacillus delbrueckii subsp. bulgaricus produced a constant capsule size regardless of the growth medium. The ability of some strains of Streptococcus thermophilus to use galactose in capsule production could reduce browning of mozzarella cheese during baking by removing a source of reducing sugar. Media that do not support capsule production may improve cell harvesting.