Antimicrobial activity of hydrogels embedded with green tea and propolis extracts against food pathogens

The aim of this work was to verify the antimicrobial activity of propolis and green tea extracts against foodborne Staphylococcus aureus and Escherichia coli. Viability of the strains, assayed in broth against eight concentration of glycerol extracts ranging from 0 to 25%, was clearly affected only at concentration higher than 6%. Then, the 24h microbial growth kinetic for both pathogens was drawn for both extracts only at 25 and 12.5%. The values of inhibition index turbidity ratio [1] were found always higher for green tea than for propolis; in addition, the inhibition index turbidity ratio produced by green tea extract was found always higher than 90% for S. aureus strains whereas it was close to 70% for the E. coli strains. Then, both extracts were incorporated into inert absorbent polysaccharide hydrogels at 10 and 70% and assayed, following the ASTM 2180, only against the most resistant E. coli O157:H7 strain. After 24 hours of contact, the concentration of viable cells showed a slight reduction for both extracts without any statistical (P<0.05) significant difference. In conclusion, antimicrobial compounds occurring in natural extracts showed a loss of antimicrobial activity when included into hydrogels. The causes of this phenomenon, still under examination, could be ascribed to a reduction in the specific antimicrobial activity, or in the mobility, of different natural compounds. Acknowledgement This work was carried out by MAIN spa and OR.MA. srl (Pisticci, Mt, Italy) within a research project funded by Italian Ministry of Economic Development within the project (DM 04/09/2013). References 1. Baruzzi F, Pinto L, Quintieri L, Carito A, Calabrese N, Caputo L (2015) Efficacy of lactoferricin B in controlling ready-to-eat vegetable spoilage caused by Pseudomonas spp. International Journal of Food Microbiology 215: 179-186.