Antimicrobial effect of water-soluble muscadine seed extracts on Escherichia coli O157:H7

Water-soluble extracts were prepared from purple (cultivar Ison) and bronze (cultivar Carlos) muscadine seeds with or without heating. The Ison extracts had strong antimicrobial activity against a cocktail of three strains of Escherichia coli O157:H7 This extract had higher acidity (pH 3.39 to 3.43), total phenolics (2.21 to 3.49 mg/ml), tartaric acid (5.6 to 10.7 mg/ml), tannic acid (5.7 to 8.1 mg/ml), and gallic acid (0.33 to 0.59 mg/ml) than did the Carlos extracts. Heat treatment on both extracts increased antimicrobial activity, possibly because of increased acidity, tartaric acid, total phenolics, and individual phenolics. Heating of Ison extracts increased ellagic acid up to 83%. Up to 10.7 mg/ml tartaric acid alone was not as effective against E. coli O157:H7 as were water-soluble seed extracts. This finding suggests the involvement of other factors, such as tannic and gallic acids, in inactivation of this pathogen. Water-soluble muscadine seed extracts may be useful for incorporation into juice and other beverage products as natural preservatives.