Oligosaccharide production and proteolysis during lactose hydrolysis using crude cellular extracts from lactic acid bacteria

The extent of the lactose hydrolysis and oligosaccharide formation through transgalactosyl reactions by crude cellular extracts (CCE) containing intracellular beta-galactosidase from disrupted Lactobacillus delbrueckii subsp. bulgaricus 11842, Lactobacillus delbrueckii subsp. lactis DMF 3078 or Streptococcus thermophilus 143 was investigated in lactose-containing buffered solutions or skim milk. Lactose hydrolysis was performed with lactose concentration ranging from 5 to 30% (w/w) at 30, 40, 50 or 60 degreesC and terminated after 120 min. The proteolytic activities of the CCEs in skim milk systems were also assessed. All CCEs produced di-, tri- and tetrasaccharides in addition to monosaccharides as major products of the lactose hydrolysis in buffered lactose solutions. However, only Lb. lactis produced tetrasaccharides at detectable levels in skim milk preparations. The amount and the rate of oligosaccharide formation were significantly (P < 0.05) affected by the origin of the enzyme, lactose concentration and temperature. The maximum oligosaccharide production by all CCEs was reached at 50 degrees C in 30% (w/w) lactose solution. St. thermophilus CCE produced significantly higher (P < 0.05) amounts of oligosaccharides than the other two CCE preparations at all lactose concentrations studied. However, Lb. bulgaricus CCE showed better lactose-hydrolyzing ability and higher proteolytic activity than the other two CCEs. The lactose hydrolysis generally proceeded faster at 50-60 degreesC than at 30-40 degreesC as opposed to the proteolytic maxima reached at 40 degreesC.