Natural antimicrobial agents as an alternative to chemical antimicrobials in the safety and preservation of food products

Background: Microbiological quality of food is of utmost importance in the food industry, so the use of food additives is essential to reduce microbial loads, which may result in food spoilage and poisoning. Objective: This study aimed to test the antimicrobial activity of three natural compounds - chitosan, ethanolic extract of propolis, and nisin - against 15 Gram-positive bacteria, 15 Gram-negative bacteria and two fungi and, also, to compare it with the antimicrobial activity of the chemical compound sodium nitrite, alone and in combination with sodium chloride. Methods: Antimicrobial activity was tested at different pH values and temperatures of incubation to simulate the presence of the pathogens in different food products and different storage conditions, as well as to determine their influence on the inhibition of microorganisms. Results: Most of the Gram-positive bacteria were inhibited at 25 µg/mL of nisin. Concentrations of 10 mg/mL of ethanolic extract of propolis inhibited fungi, most of the Gram-positive and some Gramnegative bacteria, and with concentrations of 0.65% (w/v) of chitosan, it was possible to inhibit most of the tested microorganisms. All the natural compounds tested had greater inhibitory effect against the various microorganisms compared with sodium nitrite alone and in combination with sodium chloride, in the different conditions of pH and temperature. Conclusion: This suggests that natural compounds could be good candidates for use as an alternative to chemical antimicrobials in food safety and preservation.