Effects of salt concentration and pH on structural and functional properties of Lactobacillus acidophilus: FT-IR spectroscopic analysis

• Effect of salt and pH on Lb. acidophilus on proteolytic and ACE-inhibitory activity
• Structural changes studied using Fourier transform infrared (FT-IR) spectroscopy
• Proteolytic activity of Lb. acidophilus was highest at low salt and low pH.
• ACE-inhibitory activity of Lb. acidophilus in skim milk was highest at pH 5.0.
• NaCl induced significant changes in protein and fatty acid regions of FT-IR spectra.

The effects of sodium chloride concentration and varying pH levels on the structural and functional properties of Lactobacillus acidophilus were investigated. Reconstituted skim milk was inoculated with Lb. acidophilus at varying salt concentrations (0, 1, 2, 5 and 10% NaCl) and pH levels (4.0, 5.0 and 6.0) and ACE-inhibitory activity and proteolytic activity were determined and the viable cell count was enumerated after 24 h of fermentation at 37 °C. The degree of proteolysis exhibited an increase with higher salt concentration at pH 5.0 and 6.0. ACE-inhibitory activity was found to be the highest at pH 5.0 at all salt concentrations. Fourier transform infrared spectroscopy results demonstrated significant changes occurring beyond 2% NaCl particularly at low pH (4.0). The findings revealed that significant changes occurred in amide I and amide III regions when Lb. acidophilus was subjected to varying salt concentrations.