Antibacterial activity of different degree of hydrolysis of palm kernel expeller peptides against spore-forming and non-spore-forming bacteria

Aims: The goal of this study was to determine inhibitory effect of palm kernel expeller (PKE) peptides of different degree of hydrolysis (DH %) against spore-forming bacteria Bacillus cereus, Bacillus circulans, Bacillus coagulans, Bacillus licheniformis, Bacillus megaterium, Bacillus pumilus, Bacillus stearo-thermophillus, Bacillus subtilis, Bacillus thuringiensis, Clostridium perfringens; and non-spore-forming bacteria Escherichia coli, Lisinibacillus sphaericus, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium and Staphylococcus aureus. Methods and Results: A range of DH % (50-100) of PKE peptides was prepared using alcalase, and hydrolysis conditions were determined using response surface methodology (RSM). The influence of pH (6.5-10.5), temperature (35-65 degrees C), enzyme/substrate ratio (1-5%) and substrate concentration (1-2%) were studied on the response of the DH. The antibacterial activity of different DH % of PKE peptides was tested by using disc diffusion assay and micro-broth dilution assay. According to the minimum inhibitory concentration (MIC) test on each of the PKE peptides of different DH %, the 70 DH % PKE peptide showed greater inhibitory effect compared to the 100 DH % PKE peptide against B. cereus, B. coagulans, B. megaterium, B. pumilus, B. stearothermophillus, B. subtilis, B. thuringiensis, Cl. perfringens, Lisinibacillus sphaericus and L. monocytogenes. Conclusions: The 70 DH % PKE peptides exhibited greatest overall antibacterial effect of the various peptides of PKE evaluated. Further research is needed to determine the mode of action of PKE peptides. Significance and Impact of the Study: Palm kernel expeller peptides, a natural plant product, effectively inhibited the growth of spore-forming and non-spore-forming Gram-positive bacteria. Potentially, PKE peptides could be used in food preservation and developed as antibacterial agent in the pharmaceutical industry.