Mechanism of action and utilization of isothiocyanates from mustard against Escherichia Coli O157:H7
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E. coli O157:H7 has been found to survive in dry sausages and cause disease. Isothiocyanates have been studied for their capacity to eliminate pathogens from foods and are attractive from the consumer perspective because of their natural origin. There is a need to better understand how isothiocyanates kill microorganisms and their behaviour in food matrices. It was found that glutathione and cysteine naturally present in meat can react with AIT, forming a conjugate with no or low bactericidal activity against an E. coli O157:H7. In addition, AIT presented higher anti-E. coli activity at lower pH values; therefore, it should be more efficient in acid foods. AIT was also found to inhibit the activity of thioredoxin reductase and acetate kinase; hence, enzymatic inhibition may represent a way in which AIT kills E. coli O157:H7. Mustard powder is used as a spice (active myrosinase) and/or binder (inactive myrosinase) in meat products. Both of these powders killed E. coli O157:H7 in dry fermented sausage. This was not expected since the powder lacking myrosinase is not able to produce isothiocyanates. Starter cultures and E. coli were found to consume significant amounts of glucosinolates. Pediococcus pentosaceus UM 121P and Staphylococcus carnosus UM 123M (higher myrosinase-like activity) were compared against P. pentosaceus UM 116P + S. carnosus UM 109M for their ability in reducing E. coli viability in dry sausage. Sausage batches containing powders of hot mustard, cold mustard, autoclaved mustard and no powder were prepared. Both pairs of starters yielded similar results. Reduction >5 log CFU/g of E. coli O157:H7 occurred after 31 d for hot powder and 38 d for cold powder; there was no reduction in the control. E. coli O157:H7 itself has greater effect on glucosinolate degradation than either pair of starters, which may be more important in determining its survival. Autoclaved powder caused >5 log CFU/g reduction after 18 d. This may be the result of synergistic/additive interaction among E. coli O157:H7 myrosinase-like activity, the presence of newly formed/released antimicrobials in the autoclaved powder and the multiple hurdles present in the dry sausage. Autoclaved mustard powder has potential as a novel food ingredient for the meat industry.