The effect of NaCl substitution with KCl on proteinase activities of cell-free extract and cell-free supernatant at different pH levels and salt concentrations: Lactobacillus acidophilus and Lactobacillus casei

Abstract

The aim of this study was to investigate the effect of substitution of NaCl with KCl at different pH levels and salt concentrations on proteinase activity of cell-free extract and cell-free supernatant of the probiotics Lactobacillus acidophilus and Lactobacillus casei. de Man, Rogosa, and Sharpe broth aliquots were mixed with 2 pure salts (NaCl and KCl) and 2 salt concentrations at 2 concentration levels (5 and 10%), inoculated with Lactobacillus acidophilus or Lactobacillus casei, and incubated aerobically at 37°C for 22 h. The cultures were then centrifuged at 4,000 × g for 30 min, and the collected cell pellets were used to prepare cell-wall proteinases and the supernatants used as a source of supernatant (extracellular) proteinases. The proteolytic activity and protein content of both portions were determined. After incubation of both portions with 3 milk caseins (α-, β-, κ-casein), the supernatants were individually subjected to analysis of angiotensin-converting enzyme (ACE)-inhibitory activity and proteolytic activity using the o-phthalaldehyde method. Significant differences were observed in ACE-inhibitory and proteolytic activities between salt substitution treatments of cell-free extract and cell-free supernatant from both probiotic strains at the same salt concentration and pH level.

Antagonistic effects of Lactobacillus reuteri against Escherichia coli O157:H7 in white-brined cheese under different storage conditions

“…The salt content of cheese stored in either 10% or 15% NaCl brine increased on d 1 due to the movement of Na + and Cl − ions from brine into cheese to achieve osmotic pressure balance (Ayyash et al, 2013).…”

“…reuteri, with numbers reaching ≤6.9 log 10 cfu/mL and reductions of 0.1 to 4.4 after 28-d storage. This may have been caused by continuous diffusion of all components between the cheese matrix and its brine (Ayyash et al, 2013). The E. coli O157:H7 cells were found in both white cheese (≤2.0 log 10 cfu/g) and brine (≤1.3 log 10 cfu/mL).…”

Salt Reduction in a Model High‐Salt Akawi Cheese: Effects on Bacterial Activity, pH, Moisture, Potential Bioactive Peptides, Amino Acids, and Growth of Human Colon Cells

“…However, as NaCl significantly impacts the textural and sensory properties of cheese, it is difficult to completely remove it from the product. Recent studies have shown that salt concentration (ratio of sodium chloride and potassium chloride) affects the bacterial cell membrane, viability (Gandhi and others ; Gandhi and Shah ) and proteinase activity (Ayyash and others ) of common dairy bacteria. It is therefore critical to evaluate the effects of varying salt concentrations (sodium and potassium chloride) in brine solution, which impacts the activity of bacteria in cheese.…”