Effect of yeast extract supplementation on β-galactosidase activity of Lactobacillus delbrueckii subsp. bulgaricus 11842 grown in whey.

Abstract

Lactobacillus delbrueckii subsp. bulgaricus 11842 (LB 11842) was grown in reconstituted sweet whey supplemented with 0 to 1% yeast extract. The β-galactosidase activity was determined from the hydrolysis of o-nitrophenyl- β-D-galactopyranoside (ONPG) by sonicated cultures. Shake flask cultures containing 0.2–0.8% yeast extract gave 2.5 times higher β-galactosidase activity than LB 11842 grown in sole (intact) whey. When supplementation with 1% yeast extract resulted even in a threefold increase of β-galactosidase activity. The rate of acid production increased with the addition of yeast extract, while the increase in the total cell count with increasing amount of yeast extract was slight. A maximum β-galactosidase activity of 1.08 ± 0.15 µmol ONP released per min per ml of culture was obtained using a whey based growth medium supplemented with 1% yeast extract.