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Recent studies have shown that intermediate moisture foods, while stable to microbial growth, are susceptible to chemical changes resulting in loss of quality. This study observed the effects of different water activities, citric acid contents, fat contents, and pH on lipid oxidation and non-enzymatic browning of a meat product. An intermediate moisture beef patty was produced by equilibrating and cooking the raw meat in various glycerol, water, citric acid and sodium chloride solutions. Experimental results showed that peroxide values increase with increasing water activities between Aw 0.655 and 0.818. Citric acid did not affect the formation of peroxides but prevented peroxide breakdown. There was a loss of the brown colour of the cooked meat patty and an increase in yellowness possibly due to oxidation. The loss of colouring and yellowing was greatest at low pH and high water activities. Non-enzymatic browning was not apparent. Lipid oxidation was the primary cause of the product deterioration. The shelf life was limited to three to four months by the development of rancid odours. / Land and Food Systems, Faculty of / Graduate

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The microorganisms present determine to a great extent the quality of cured meat. Some of them may have unfavorable effects on the color and flavor, whereas others are known to have beneficial effects on these quality factors. Yeasts, bacilli, and streptococci were found to be predominately present in a cover pickle which had been recently used for curing hams in a commercial meat packing plant. They were isolated and their characteristics studied. All three organisms rapidly reduced resazurin and litmus milk, but failed to reduce nitrates. They were salt-tolerant and grew best at about 21°C. The yeasts did not produce carbon dioxide when grown in lactose or glucose fermentation tubes. The effect of these organisms on the rate of color development during curing of pork was studied. Ham from a freshly slaughtered hog was cut aseptically and ground. It was blended with a sterile curing solution and inoculated with each of the test organisms. It was then incubated at 60°F. for 24 hours and finally heated at 120°F. The color development throughout curing was studied with the Photovolt Spectrophotometer with a reflectance attachment. The pH, oxidation-reduction potentials, and plate counts were determined during curing at 60°F. The results indicated that the organisms tested improved the color of cured meats by reducing the oxidation-reduction potential of the meat during curing. / Graduation date: 1955

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Graduation date: 1950

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The over-tenderization of irradiated-sterilized meat is one of the more important adverse effects resulting from the use of irradiation for the preservation of meat. Although research has been reported on the activity and effect of the inherent proteolytic enzymes of irradiated meat, very little work has been directed toward the intimate causes of the textural problems induced by the irradiation treatment. In this study, the influence of irradiation-sterilization on some of the muscle characteristics involved in meat texture was investigated in an attempt to elucidate the over-tenderizing action of irradiation. In addition, the influence of treating the meat by several means prior to irradiation was also investigated to determine their effects upon the texture of the meat. Information relative to the above objectives was obtained by using analytical methods designed to show changes in muscle protein charges, water-holding capacity, acidic and basic groups, bound and free minerals, and disc electrophoretic analysis of the glycine soluble extracts of the treated and control samples. The results showed that the irradiation-sterilization of beef muscle at 4.5 megarads caused tenderization of the meat. Beef soaked in an equal amount of distilled water for 72 hours at 38°F prior to heat inactivation of the enzymes and irradiation was much firmer in texture than the unsoaked samples. Beef heated to an internal temperature of 160°F prior to irradiation also resulted in meat having a firm texture. However, irradiation tends to reverse the effects of both soaking and heating and/or the combination of these two treatments. When soaking, heating and irradiation are combined in one treatment, these factors tend to exert their effect individually and by different mechanisms. Soaking the meat appears to cause a partial denaturation and a net loss of anions of some of the muscle proteins resulting in a shift in the isoelectric region of such meat to a higher pH which results in a greater loss of water upon cooking and thus a firmer texture. Heating the meat to an internal temperature of 160°F results in a partial denaturation of the proteins and probably leads to the formation of stable cross linkages and a "salting-out" effect which may be responsible for a decrease in the water-holding capacity. Thus, meat would have a tighter or more "closed" structure and firmer texture. Irradiation exerts a fragmentation effect upon the beef muscle proteins. These fragments seem to be held together by hydrogen bonds and/or electrostatic forces. The fragmentary alterations of the muscle proteins, the incorporation of water within the fragments, and possibly a "salting-in" effect, appear to be the major factors responsible for effects of irradiation on beef muscle texture. The zinc cations appear to be involved with the heat-labile proteins or enzymes which are denaturated by heating to 160°F. The pH-water holding capacity curves were found to be a valuable technique for investigating some of the biochemical changes in the muscle proteins. / Graduation date: 1963