Influence of pH and sodium chloride on kinetics of thermal inactivation of the bacteriocin-like substance P34.

AIMS: To investigate the kinetics of thermal inactivation of the bacteriocin-like substance P34 at different pH and sodium chloride concentration. METHODS AND RESULTS: Samples of bacteriocin were treated at different time-temperature combinations in the range of 0-300 min and 90-120°C and the kinetic parameters for bacteriocin inactivation were calculated. For all treatments, the thermal inactivation reaction fitted adequately to first-order model. D- and k-values were smaller and higher, respectively, for pH 4·5 than for 6·0 or 7·0, indicating that bacteriocin P34 was less thermostable at lower pH. At 120, 115 and 100°C, the addition of sodium chloride decreased thermal stability. For other temperatures, addition of NaCl increased stability of the peptide. The presence of greater amount of the salt (50 g l(-1) ) resulted in a higher thermal stability of bacteriocin P34, suggesting that the reduction in water activity of the solution interfered on the stability of the peptide. CONCLUSIONS: Based on an isothermal experiment in the temperature range of 90-120°C, and by thermal death time models, bacteriocin P34 is less heat stable at low pH and has increased thermal stability in the presence of NaCl. Addition of NaCl improved the stability of the peptide P34 at high temperatures. SIGNIFICANCE AND IMPACT OF THE STUDY: Studies on kinetics of thermal inactivation of bacteriocins are essential to allow their proper utilization in the food industry.

Bacteriocin-like substance production by Bacillus licheniformis strain P40.

AIMS: To investigate the production of bacteriocin-like compounds by Bacillus spp. isolated from the Amazon basin. METHODS AND RESULTS: An antimicrobial substance produced by Bacillus licheniformis strain P40 was inhibitory to a broad range of indicator strains, such as Listeria monocytogenes, Bacillus cereus and clinical isolates of Streptococcus spp. The compound was stable at 100 degrees C, but lost its activity when treated at 121 degrees C/103.5 kPa for 15 min. It was resistant to the proteolytic action of trypsin and papain but sensitive to pronase E and was stable within a wide range of pH (3-11). The substance was bactericidal and bacteriolytic to L. monocytogenes. CONCLUSIONS: An antibacterial peptide produced by Bacillus licheniformis was characterized, presenting a broad spectrum of activity against pathogenic and spoilage organisms. SIGNIFICANCE AND IMPACT OF THE STUDY: The identification of a substance active against important pathogens addresses an important aspect of food safety.