No 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. Keywords 167Czech J. Food Sci. Vol. 19, while the maximal β-galactosidase activity (measured by freezing point depression was obtained after 8 hrs.The purpose of the present study was to examine the production of active β-galactosidase LB 11842 grown in sweet whey supplemented with various amounts of yeast extract. MATERIALS AND METHODSMicroorganisms and Media: LB 11842 was obtained from University of Alberta, Department of Agricultural, Food and Nutritional Science. The culture was propagated every two weeks in sterile MRS broth (Difco, Detroit, MI) enriched with 1% (w/v) α-lactose (Fisher Scientific Co., New Jersey). To prepare the culture for fermentation in the whey based broth, about 0.5 ml of refrigerated culture was added to 5 ml of the above MRS/lactose broth. After incubation at 43°C for 8 to 12 hrs, 1 ml of active culture was used to inoculate 150 ml of sterile broth containing 3% (w/v) reconstituted whey powder and 1.3% (w/v) MRS powder (WMRS broth). This culture was incubated at 43 ± 1°C with shaking at 140 ± 30 RPM in a controlled environmental incubator shaker (New Brunswick Co., USA) for 1012 hrs.The whey based broths used for the fermentations were made by dissolving 6 g spray dried whey powder (Kraft, Montreal) per 100 ml of distilled water and adding the desired amount of powdered yeast extract (Fermtech, BDH Inc., Toronto). Flasks containing 150 ml of this whey-based broth were autoclaved at 121°C for 15 min.Fermentation: Flasks containing 150 ml of sterile whey based broth supplemented with 0, 0.2, 0.4, 0.6, 0.8 or 1% yeast extract (YE) were inoculated with 5 ml of the culture grown in WMRS broth. The culture was grown in the incubator shaker at 4043°C and 140 ± 30 RPM. The pH was monitored using a combination pH probe sterilized with 70% ethanol and maintained at pH 5.5 ± 0.3 by the manual addition of 2M NaOH (Fisher Scientific Co, Inc., USA). Cell growth was followed by direct microscopic enumeration and the rate of acid production was determined as the consumption of 2M NaOH.Measuring β β β β β-galactosidase Activity: A method of measuring β-galactosidase activity using o-nitrophenyl-β-Dgalactopyranoside (ONPG) described by MAHONEY...