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 Ca 2+-free buffer. The crude proteinase extract showed the highest activity at pH 7.2 and 37 ºC. 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 P 1-type proteinases, since it completely hydrolysed only β-casein, showing very low activity towards α-casein.

Chemically Defined Medium for Optimization of Proteolytic Activity of Lactobacillus bulgaricus 761N

“…In the current study, the optimum pH was pH 7.0 (Table 4) and decreased towards the acidity. These findings agreed with Fira, [39], Kabadjova-Hristova [33], and El-Ghaish et al [38], with some variations but with the same trend. The variations might be due to the difference in bacterial species.…”

“…Other literature elicited that the proteolytic activity increases with increase in incubation time till 36h of incubation then the proteolytic activity begins to decline [36] that disagree with the current study and the previous study by Tufail et al [35]. That difference may be owing to species difference or isolation origin as it was investigated by Kabadjova-Hristova et al [33]. Kabadjova-Hristova et al [33], have found that according to the literature of Pereira et al [37], the proteinases of L. curvatus and L. homohiochii showed maximum activity in the early exponential phase, that findings disagreed with their investigations and informed that the disagreement is owing to the origin of the strain used which was isolated from kefir grains that presented too complex media.…”

“…Further degradation into smaller peptides and amino acids that can pass through cell membrane is achieved by peptidases of lactic acid bacteria [31,32]. The findings of Kabadjova-Hristova, et al [33] approved that Lactobacillus (L. kefir DR22x) had cell-wall-bound proteinases with an extracellular location. Where y = Test -Control, x = Proteolytic activity (U/ml/min).…”

“…Generally, but within limited range, the decrease in temperature was found to be accompanied with an increase in the proteolytic activity. Kabadjova-Hristova, et al [33], and El-Ghaish et al [38], have reported that the highest proteolytic activity was at 37º C and that raising the temperature up to 42º C slightly affected the proteolytic activity. The current study recorded that the optimum temperature was at 35º C, and a slight decrease in proteolytic activity with increasing temperature to 37º C and then 42º C. That optimum temperature agreed with the previous work by Tufail et al [35].…”

“…That difference may be owing to species difference or isolation origin as it was investigated by Kabadjova-Hristova et al [33]. Kabadjova-Hristova et al [33], have found that according to the literature of Pereira et al [37], the proteinases of L. curvatus and L. homohiochii showed maximum activity in the early exponential phase, that findings disagreed with their investigations and informed that the disagreement is owing to the origin of the strain used which was isolated from kefir grains that presented too complex media. …”