Lactose hydrolysis by sonicated cultures of Lactobacillus delbrueckii subsp. bulgaricus 11842

Growth and lactose hydrolysing characteristics of a common dairy micro-organism, Lactobacillus delbrueckii subsp. bulgaricus strain 11842 (LB 11842) were determined to enable potential use in a proposed method of lactose hydrolysis by disrupted dairy cultures. LB 11842 was grown aerobically in MRS medium, sonicated to disrupt the organisms, then added to various lactose-containing substrates. The progress of hydrolysis was followed by freezing point changes. Cultures added to 5% lactose test solutions resulted in 20% and 63% of the lactose being hydrolysed after 3 hours at 7° and 51°C, respectively. Enzyme activity was not hindered in 30% lactose solution and the rate was acceptable at 7°C in skim milk. Cultures were sonicated in Na+ or K+ buffers at various pH levels, then held at various temperatures, before adding to lactose test solutions. Cultures sonicated in K+ buffer had higher activity and stability than those in Na+ buffer; both were the highest at pH 6 and 7. Holding at 61°C for 60 minutes caused 70% loss of activity with K+ ions; with Na+ loss of activity was almost complete. As an incidental observation made during the propagation of the organism, there were major differences in growth on two commercial brands of MRS medium, which was also the case with four other strains of Lactobacillus. LB 11842 shows promise as a suitable source of beta-galactosidase for use in the proposed process as the enzyme showed acceptable activity at a wide temperature range with high thermostability especially in the presence of K+ ions.