Antimicrobial activity of Thai traditional medicinal plants extract incorporated alginate-tapioca starch based edible films against food related bacteria including foodborne pathogens

摘要

In Thai traditional medicine, different plant extracts are known to have a bactericidal or at least a bacteriostatic effect on bacteria and/or fungi. In Thailand, medicinal plants have been used safely since ancient times as herbal medicines and also as food colouring and flavouring agents. The application of selected plant extracts to foods could prevent foodborne diseases and food spoilage. In this study the antimicrobial activities of Andrographis paniculata (Burm.f.) Nees, Curcuma zedoaria (Christm.) Roscoe, Garcinia mangostana Linn., Hibiscus sabdariffa Linn., Musa sapientum Linn., Nelumbo nucifera Gaertn., Piper betle Linn., Psidium guajava Linn., and Punica granatum Linn. used by Thai practitioners of traditional medicine were investigated against different strains of food related bacteria, including 3 strains of Escherichia coli 2 strains of Salmonella Typhimurium, Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, 1 strain of Bacillus subtilis, Vibrio parahaemolyticus, Yersinia enterocolitica, and 2 strains of Pseudomonas sp. Minimum Inhibitory Concentration (MIC-value) and Minimum Bactericidal Concentration (MBC-value) of hot water extracts, ultra sonicated extracts, and ethanolic extracts were determined by using the method described by the DVG (Deutsche Veterinärmedizinische Gesellschaft). From the results, it can be investigated that all crude extracts exhibited antimicrobial activity at least against one of the test organisms at concentration of 15.0 g/100 ml or lower. The results also indicated that the antibacterial activity of hot water extracts was better than ultra sonicated extracts and the ethanolic extracts exhibited the best antibacterial activity. Among the ethanolic extracts, the highest inhibitory activity was caused by Hibiscus sabdariffa Linn. and Piper betle Linn. The antimicrobial activity of both extracts against the test organisms was determined as Minimum Inhibitory Concentrations (MIC-value) ranging from 0.1 to 3.0 g/100 ml and 0.1 to 2.5 g/100 ml, as well as Minimum Bactericidal Concentrations (MBC-value) ranging from 0.2 to 3.5 g/100 ml and 0.2 to 1.5 g/100 ml for the ethanolic extracts of Hibiscus sabdariffa Linn. and Piper betle Linn., respectively. Bactericidal activity of the extracts was determined using a modified suspension test method according DIN EN 1040 (Quantitative suspension test for the evaluation of basic bactericidal activity of chemical disinfectants and antiseptics) and DIN EN 1276 (Quantitative suspension test for the evaluation of bactericidal activity of chemical disinfectants and antiseptics used in food, industrial, domestic, and institutional areas). Concentrations of 15.0 g/100 ml of the pure ethanolic extract of Curcuma zedoaria (Christm.) Roscoe, Garcinia mangostana Linn., Hibiscus sabdarifa Linn., and Piper bettle Linn., demonstrated a lethal effect within 15 seconds contact time. The others required more than 1 hour contact time to inactivate the test organisms. Among the test organisms, spore forming Bacillus spp. exhibited the highest resistance. The bactericidal activity of Thai traditional medicinal ethanolic extracts was decreased when interfering substances were added. To determine the bactericidal activity on surfaces the ethanolic extract of Piper betle Linn. was coated on stainless steel discs, but the results indicated that stainless steel discs were not the suitable surfaces to use as an artificial antimicrobial surface.To simulate the application under use conditions the antimicrobial activity of Alginate-Tapioca starch-based edible films were studied by incorporation of those ethanolic extracts as a natural antimicrobial agent. The edible films exhibited antimicrobial activity against bacteria tested by using agar diffusion assay. The presence of 20.0 % v/v of those extracts in the edible films had the ability to inactivate the test organisms within 24 hours incubation time. These results revealed that ethanolic extracts of those medicinal plants had a good potential to be incorporated to make antimicrobial edible film or coating for various food applications. The cytotoxic effect of those ethanolic medicinal plants extract were also determined using 4 different cell lines. The results of the cytotoxicity screening showed that the activity of the extracts correlates more with their effect on microorganisms than with their possible effect on the mucous membranes of human. The antimicrobial edible films and coating were studied in model food. The results demonstrated that the edible film wrapping method had advantages and showed more excellent benefit in the application with food than the edible coating method. In addition, the storage temperature was an important factor. Antimicrobial edible films presented higher activity at room temperature than under cold conditions (4ºC). In summary, the extract of those Thai traditional medicinal plants by itself or incorporated into edible films had potential for inhibiting or inactivating foodborne pathogens or food related bacteria in microbiological media and model food system; therefore, they could be useful as a method for controlling growth of foodborne pathogens and food related bacteria.