88D-4 |
Growth of histamine-producing bacteria in tuna (Tunnus thynnus) and its possible reduction by lactic fermentation |
S. GUILLÉN VELASCO, E. Ponce-Alquicira, and I. Guerrero Legarreta. Departamento de Biotecnología, Universidad Autónoma Metropolitana-Iztapalapa, Ap. Postal 55-535, Mexico City, 09340, Mexico Red-muscled fish such as tuna, contains high amounts of free histidine. This aminoacid is decarboxylated by enzymes produced by enterobacteriacea, such as Morganella morganii. The reaction’s final product, histamine, is a toxic biogenic amines also responsible of rotten fish off-odor. Lactic acid fermentation in food materials efficiently controls the proliferation of several spoilage microorganisms, enterobacteria among others. It is therefore feasible to control the growth of M. morganii in fish muscle, reducing histidine-decarboxylase production and decreasing histamine levels. Tuna were caught in the Gulf of Mexico and transported in ice to Mexico City. Muscle samples were finely ground and added with 5% dextrose. They were divided into four batches and inoculated with: Staphylococcus carnosus; S. carnosus and M. morganii; and M. morganii. One batch was left uninoculated as control. The samples were vacuum packaged and stored at 20oC during a total study time of 8 days. The response variables were: pH, enterobacteria population and histamine formation analyzed by HPLC. Samples inoculated with S. carnosus showed a decrease in pH up to 4.5, in these samples the growth of native enterbacteria was limited. M. morganii population was reduced by 3 log cycles in samples inoculated with S. carnosus and M. morganii. Histamine concentration was reduced from 43 mmoles/g tissue in muscle inoculated with M. morganii, to 33 mmoles/g tissue in samples inoculated with M. morganii and S. carnosus. It seemed that the histidine-decarboxylase activity is not controlled by number of microorganisms but only by the presence of the enzyme-producing strain. Inoculation of tuna with S. carnosus inhibited the growth of intentionally added M. morganii and native enterobacteria and consequently reduced histamine concentration. Lactic fermentation can be a means to reduce enterobacteria growth in red-muscled fish.
Session 88D, Food Microbiology: General
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