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The effects of electron beam irradiation and infusion of L-ascorbic acid on the preservation of quality of fresh ground beef patties Wong, Peter Yan Yung

Abstract

The objectives of this thesis were to assess the effectiveness of electron beam irradiation (e ⁻ beam) at 5, 10 and 20 kGy in reducing bacterial count in fresh ground beef patties of 4, 17 and 30% fat and to evaluate the effects of infusing L-ascorbic acid (LAA) into beef carcasses on the quality of irradiated fresh ground beef patties of 4, 17 and 30% fat. Aqueous and emulsion model systems, exposed to ultraviolet and electron beam irradiation, were first used to determine the catalytic activity of hemoglobin, the depletion of LAA and the effects of LAA and e" beam on the degree of lipid oxidation. Hemoglobin generated 50% less hydroxyl radicals than ferrous chloride in the Fenton reaction, indicating minor catalytic activity. An increase in irradiation dosage and storage time drastically decreased the concentration of lOmM L-ascorbic acid. Both ultraviolet and e" beam irradiation induced lipid oxidation in a dose-dependent manner, which was further enhanced by the prooxidant activity of 10 mM LAA. The 500 mM LAA exhibited the opposite effect. The effectiveness of electron beam irradiation in controlling microbial growth was then evaluated in ground beef patties made from LAA infused beef carcasses. Viable bacteria were not detected in ground beef patties receiving irradiation at dosages of 5, 10 and 20 kGy. The addition of tallow to increase total crude fat content in the beef patties led to an increase in bacterial counts. An increase in pH of patties was could have been attributed to the metabolic by-product generated by microorganisms. Finally, the physicochemical characteristics of the infused ground beef patties were evaluated. An increase in irradiation dosages resulted in an increase in lipid oxidation in the beef patties. LAA also increased lipid oxidation, as well as, deoxymyoglobin oxidation in the beef patties. Higher fat content resulted in higher lipid oxidation and pigment oxidation in the beef patties. Hardness attribute of the ground beef patty was significantly increased by the addition of fat. In general, the application of low dosage of e ⁻ beam to lean ground beef patties without the addition of LAA is optimum in preserving quality.

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