Purpose: The purpose of this research was to study antimicrobial effects of plant extracts as potential preservatives in seafood products and to identify the primary antimicrobial compounds in plant extracts.
Methods: Four plants, Pomegranate peel (“PP”, Punica Granatum L.), Chinese gallnut (“CG”, Galla chinensis), forsythia (“FS”, Forsythia suspensa) and Baikal skullcap (“BS”, Scutellaria baicalensis) were ground and extracted with 70% methanol, respectively. Five concentrations of each extract (0.008, 0.04, 0.2, 1.0, and 5.0 mg/ml) were applied to V. parahaemolyticus and L. monocytogenes cultures which were then incubated at 37°C, and sampled after 8, 24, and 96 hours. Samples were spread plated, incubated and enumerated to determine the level of inhibition by plant extracts. Extracts from each plant were analyzed by HPLC, and then fractions were collected based on elution time and tested for their antimicrobial activity against V. parahaemolyticus and L. monocytogenes using agar diffusion methods.
Results: Both CG and PP extracts, with concentrations no lower than 1 mg/ml, significantly inhibited both pathogens by up to 4 logs. No inhibition was observed with FS and BS extracts, except for BS at 5 mg/ml against V. parahaemolyticus. Inhibitory activities of CG and PP extracts were distributed among all fractions, thus in each plant extract more than one compound contributed to inhibition, most of which were categorized as flavonoids, hydrolysable tannins and their pentosides or hexosides.
Significance: Traditional Chinese medicine plant-source antimicrobial compounds can inhibit foodborne pathogens including V. parahaemolyticus and L. monocytogenes, and therefore can be potential natural preservatives for RTE foods.