Impact of NaCl substitution with KCl on cell-wall extract and cell-free supernatant proteinase activities of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus and Lactobacillus acidophilus and Lactobacillus casei at different pH and salt levels

Abstract

To reduce salt concentration in cheeses by substitution with KCl, it was important to study the effect of salt substitution on starter culture proteinases which play a vital role in ripening and texture profile of cheeses. The objective of this study was to examine the effect of NaCl substitution with KCl at different pH levels (6.0, 5.5, and 5.0) and salt concentrations on proteinases activity of cell-wall and supernatant of Lactobacillus delbrueckii ssp. bulgaricus 11824, Streptococcus thermophilus MS as well as of Lactobacillus acidophilus and Lactobacillus casei was investigated. MRS broths were mixed with 4 salt substitutions at 2 different concentrations (5% and 10%) and incubated individually at 37°C for 22 h. The collected cell pellets were used to prepare cellwall proteinases and the cell-free supernatants were used as source of supernatant proteinases. The proteolytic activities and protein contents of both portions were determined. The supernatants after incubation of both portions with 3 milk caseins (α, β, kappa-casein) were subjected to ACE-inhibitory activity and proteolytic activity by OPA method. Significant differences were observed in ACE-inhibitory activity and OPA between salt substitutions of cell-wall extract and cell-free supernatant of LB and ST at same salt concentration and same pH level. The conclusion is that there were significant effects of pH and salt substitution on all measured variables.