Effect of Some Herb and Spice Extracts Against Pathogenic Bacteria in Minced Pork Meat

Abstract

This study investigated the antimicrobial actions of Zanthoxylum limonella, Neem leaves, garlic and galangal from Laos to inhibit some foodborne pathogens, particularly Escherichia coli, Salmonella enterica serovar Typhimurium and Staphylococcus aureus. Herb extracts were obtained by hydro distillation at 100ºC for 4 h at atmospheric pressure or by super critical fluid extraction at 45ºC and 17 MPa for 4 h. The antimicrobial activities of the extracts were then studied against three pathogens on microbiological media using Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC) and agar disc diffusion assay, and applied on minced pork meat. Minced pork meat sample was added with different concentrations of herb extracts, such as 0.30%, 0.60% and 0.90%. At the end of the study, minced pork meat samples were processed with microwave power at levels of 450 and 850 watts for 15 s. The highest yield extract was determined in the Z. limonella extract obtained by hydro distillation, which was 6.32±0.40%. In the MIC method, the Z. limonella extract from hydro distillation and galangal extract obtained by super critical fluid extraction at a concentration of 12.50% could inhibit all of the studied pathogens. However, it was only the Z. limonella extract produced by hydro distillation that could kill the pathogens at the lowest concentration of 12.50%. Regarding the agar disc diffusion assay, Z. limonella extract from hydro distillation at 100% concentration could inhibit E. coli for 15.67±1.81 mm, which was not significantly different to that of an antibiotic control of 10 μg methicillin (p≥0.05). For S. Typhimurium and Staph. aureus, the highest inhibition could be significantly achieved by galangal extract obtained by super critical fluid extraction at 100% concentration for 25.87±0.68 and 25.77±0.68 mm, respectively (p<0.05). These inhibition zones were significantly higher than their antibiotic controls of 10 μg amoxycillin and 10 μg methicillin, respectively. The highest reduction in the numbers of investigated pathogens in minced pork meat was achieved by Z. limonella at the concentration of 0.90%, which was 2.86±0.26 log cfu/25 g for E. coli, 3.63±0.02 log cfu/25 g for S. Typhimurium and 3.33±0.96 log cfu/25 g for Staph. aureus. For the study of the effect of microwave treatment on the examined bacteria in minced pork meat, it was found that Staph. aureus was more sensitive than E. coli and S. Typhimurium in the microwave heating at 850 watts with 0.30% Z. limonella extract. The survival number of Staph. aureus was 1.820.09 log cfu/25 g.