Lactose hydrolysis by disrupted thermophilic lactic acid bacteria

A novel process for the lactose hydrolysis in dairy systems was evaluated from the technical feasibility standpoint, using beta-galactosidase-containing crude cellular extracts (CCE) from a mechanically disrupted culture of Lactobacillus delbrueckii ssp. bulgaricus ATCC 11842 (LB11842).; The maximization of beta-galactosidase (beta-gal) activity was attempted by optimizing growth conditions of LB11842 cultivation. Enrichment of whey or whey permeate based media with whey protein preparations, yeast extract or MRS slightly improved culture growth and beta-gal activity, but was inferior to cultivation in sterile skim milk. In contrast to NaOH or KOH, which had a similar effect, the NH4OH improved biomass production and beta-gal activity with concomitant proteolytic activity suppression and enhancement of exopolysaccharide formation.; The CCEs {09}from three{09}potential sources of the beta-gal activity, LB11842, Lactobacillus delbrueckii ssp. lactis DMF 3078 and Streptococcus thermophilus 143 (St143), were compared for lactose hydrolysis, as well as for transferase and proteolytic activities. The highest lactose hydrolysis rate and proteolytic activity were achieved using LB11842. Different neutralizers had no effect on the rate constant kcat which was significantly different (p ≤ 0.05) among the CCEs, with temperature dependence following the Arrhenius kinetics. St143 CCE exerted significantly (p < 0.05) higher transferase activity. The maximum oligosaccharide formation by all three CCEs was around 50°C. Maximum proteolytic activity, using the response surface methodology, was predicted to be around 43°C.; The preservation of beta-gal activity in LB11842 CCE preparations by spray- or freeze-drying was a function of process conditions and type of adjuncts. The presence of lactose was essential for almost complete activity preservation. Enzyme activity after spray drying was highly dependent on inlet temperature and residual moisture after drying.; Addition of 2 or 4% CCE to skim milk resulted in increased sweetness as well as noticeable off-flavors, probably carried over from the beta-gal production step. Use of 1% KOH CCE resulted in the products being closest to the control skim milk, while the NH4OH imparted grossly detrimental taste. The proposed lactose hydrolysis process using the CCE technology appeared to be technically feasible in selected dairy systems, while other possible applications of the CCE approach were also identified.