Disruption of Lactobacillus delbrueckii ssp. bulgaricus 11842 cells for lactose hydrolysis in dairy products: a comparison of sonication, high-pressure homogenization and bead milling

Abstract

Cultures of Lactobacillus delbrueckii ssp. bulgaricus 11842 grown on whey supplemented with yeast extract were subjected to treatments using sonication, a high-speed bead mill, and a high-pressure homogenizer. The various means of disruption were compared by the release of intracellular β-galactosidase and by scanning electron microscopy (SEM). The β-galactosidase activity was measured using o-nitrophenyl-β- d-galactopyranoside (ONPG). In general, the release of active β-galactosidase was not affected by cell concentrations in the range of 12–46% (wet wt.). The maximum activity was observed after 2–3 min of bead milling and after three passages through the high-pressure homogenizer (135 MPa). The amount of active β-galactosidase released by homogenization after one passage at 200 MPa was comparable to that released between two or three passages at 135 MPa. Sonication was not as effective as the bead mill or the high-pressure homogenizer with respect to the release of β-galactosidase or the break-up of cells as evidenced by SEM and TEM. Both bead milling and high-pressure homogenization appear to be suitable for the large-scale disruption and release of β-galactosidase from L. delbruekii ssp. bulgaricus 11842.