Graduate Thesis Or Dissertation
 

The nature of hydrative changes and cationic shifts in the over-tenderization of beef muscle resulting from irradiation

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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.
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