Aqueous and ethanolic extracts of propolis for the control of tyramine production by food-borne pathogens

Abstract

The influences of aqueous and ethanolic extracts of propolis (1%) on growth of common Gram-negative (Salmonella Parathyphi A, Campylobacter jejuni, Yersinia enterocolitica and Klebsiella pneumoniae) and-positive (Listeria monocytogenes, Staphylococcus aureus and Enterococcus faecalis) food-borne pathogens and their biogenic amines (BAs) production were examined in tyrosine decarboxylase broth (TDB). The highest growth inhibitory activity was observed against Gram-negative S. Paratyphi A in the existence of ethanolic and aqueous extracts of propolis, with 2.49 and 1.9 log reduction, respectively. Ethanolic extracts of propolis were more effective than that of aqueous extract on growth inhibition of L. monocytogenes (p<0.05). Both extracts of propolis had significant effect on reducing ammonia production by bacteria (p<0.05). Tyramine, dopamine, agmatine and spermine were major amines formed in TDB. Tyramine production was the lowest with S. Paratyphi A (1.94 mg/L) and highest with E. faecalis (254.93 mg/L). The existence of ethanolic propolis extracts in TDB led to significantly fewer tyramine production by Gram-positive S. aureus, L. monocytogenes and E. faecalis, and Gram-negative C. jejuni (p<0.05). Histamine produced lower than 1.3 mg/L by all food-borne pathogens. Ethanolic extracts of propolis generally led to lower histamine production by bacteria. The influence of propolis on BAs production varied according to type of extracts, specific BAs and bacterial strains. However, the aqueous of propolis generally showed a synergistic effect on most of BAs mainly tyramine production by bacteria. Thus, the use of propolis ethanolic extracts appeared to be more suitable than aqueous extract to control tyramine production in foods.