Evidence for proteolytic activity of lactobacilli isolated from kefir grains

Abstract

The proteolytic activity of 276 natural isolates from kefir grains was investigated. Evidence for extracellular proteolytic activity was demonstrated for 49 Lactobacillus strains. One strain, Lactobacillus kefir DR22x, was selected as a producer of proteinases. Lactobacillus kefir DR22x strain produces a cell-wall-bound proteinase. The proteinase was removed from the cell envelope by washing the cells with a Ca2+ free buffer. The crude proteinase extract showed the highest activity at pH 7.2 and 37 °C. The proteolytic activity was shown to be maximal in the late exponential growth. A study using several protease inhibitors suggested that this activity is associated with serine-type proteases. Considering the substrate specifity, the enzyme is similar to the lactococcal P1—type proteinases, since it completely hydrolysed only β-casein, showing very low activity towards α-casein. © 2006 Taylor and Francis Group, LLC.