Call number: LD2668 .T4 1978 K85 / Master of Science

Call number: LD2668 .T4 1964 W42 / Master of Science

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

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Thesis (PhD (Food Sc))--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Ostrich meat has become increasingly popular in South Africa and abroad, driven by the health conscious trend and ostrich meat’s natural low intramuscular fat, high polyunsaturated fatty acid and low cholesterol content. This increased demand led to the investigation of novel packaging regimes to improve its attractiveness and shelf-life. Different modified atmospheric packaging regimes were studied for fresh and frozenthawed ostrich M.iIliofibularis steaks stored at ±4°C for 10 days. Oxygen MAP (30 CO2:70 O2) was applied with great success to fresh steaks, and resulted in significantly improved colour stability, decreased drip loss and a 10-day shelf-life. Oxygen MAP of frozen-thawed ostrich steaks was not successful as the colour deteriorated within 3 days, coupled with high lipid and protein oxidation. The microbial shelf-life was not influenced by freezing and thawing. The use of nitrogen MAP (30 CO2:70 N2) as an alternative to vacuum packaging for fresh and frozen-thawed ostrich meat was inconclusive due to trace amounts of residual oxygen in the headspace accelerating myoglobin oxidation by depleting the metmyoglobin reducing activity. The differences in oxidative stability of the fresh and frozen-thawed ostrich meat led to the investigation of the source of these differences and a system that would allow control over the freezing and thawing practice. This was supported by the industry that is under increasing pressure to reduce the excessive (15-20%) thaw weight loss that is continually reported. Subsequently, a mathematical prediction model based on the control volume approach was developed that predicted the rate of freezing and thawing of intact whole vacuum-packed ostrich muscle. The model predicted with greater accuracy than existing models, and can be used successfully by the industry to optimally design, control and operate their systems. Furthermore research was conducted to investigate the effect of different freezing and thawing rates on the ice crystal formation and the quality of ostrich M. femorotibialis stored at ±4°C post freeze/thaw. Five characteristic freezing rates (FR (time from 0°C to -7°C): 1, 2, 4, 8, 24h) were paired with five characteristic thawing rates (TR (time form -7°C to 0°C): 1.5, 3, 6.5, 14, 21h) in a completely randomised block design. Results showed that thawing had no impact on any of the tested quality parameters, including thaw loss. Freezing rate however did influence the ice crystal formation and at a characteristic freezing rate of one hour (FR_1h) only intracellular ice crystals were observed throughout the M. femorotibialis leading to the lowest thaw loss (2.57%) and highest shear force. Freezing rate of 2h, 4h and 8h (FR_2h, FR_4h and FR_8h) were dominated by extracellular ice crystals. FR_2h and FR_8h showed major dehydration of the muscle fibres and excessive distortion of the muscle fibre matrix that led to significantly lower oxidative stability. FR_24h (approximately commercial rates) formed columns of ice from the surface to the centre of the meat resulting in the highest thaw loss (6.24%). FR_4h was judged to deliver the best quality product with moderate thaw (3.93%) and drip loss, low cooking loss, good colour stability and extremely low TBARS. FR_4h is an achievable rate of freezing for the industry and if implemented should decrease the thaw loss problem as well as increase revenue and throughput in the processing facility. / AFRIKAANSE OPSOMMING: ‘n Hedendaagse strewe na ‘n gesonde lewenstyl tesame met die natuurlike lae vetinhoud (d.i. hoë poli-onversadigde vetsure en lae cholesterolvlak) van volstruisvleis het gelei tot ‘n toename in die nasionale en internasionale aanvraag. Hierdie het ook die behoefte laat ontstaan om nuwe verpakkingstegnieke te ondersoek om sodoende die aanvaarbaarheid en rakleeftyd van die produk te verleng. Die invloed van verskeie gewysigde atmosferiese verpakkingsmetodes (GAV) op die kleurstabiliteit, drupverlies en rakleeftyd van vars en bevrore/ontdooide volstruisvleis (spesifiek M. Iliofibularis), gestoor by ±4°C vir 10 dae, is ondersoek. Die suurstof GAV (30 CO2:70 O2) van vars volstruisvleis het ‘n verbetering in kleurstabiliteit, verlaagde drupverlies en 'n verlengde mikrobiese rakleeftyd (10 dae) tot gevolg gehad. Die suurstof GAV van bevrore-ontdooide volstruisvleis het geen voordelige effek op kleurstabiliteit en rakleeftyd getoon nie. Die bevrore/ontdooide monsters het totaal verkleur na 3 dae en ‘n hoë vlak van lipied- en proteïenoksidasie is waargeneem. Die bevriesing en ontdooiing het geen invloed op rakleeftyd gehad nie. Die moontlikheid om stikstof GAV (30 CO2:70 N2) as 'n alternatief tot vakuumverpakking vir vars en bevrore/ontdooide volstruisvleis te gebruik, is beïnvloed deur die teenwoordigheid van oorblywende suurstof in die lugruimte van die GAV, met ‘n gevolglike toename in die tempo van mioglobien oksidasie as gevolg van ‘n afname in die metmioglobien reduksie aktiwiteit. Die verskil in die oksidatiewe stabiliteit van vars en bevrore/ontdooide volstruisvleis het gelei tot ‘n verdere ondersoek na die oorsaak van die verskille en die ontwikkeling van ‘n moontlike protokol om die oksidatiewe stabiliteit en dus rakleeftyd van volstruisvleis, te verbeter en bestuur. Die behoefte aan so ‘n protokol is beklemtoon deur die bedryf wat onder toenemende druk verkeer om buitensporige ontdooiingsverliese (15-20%) te verminder. ‘n Wiskundige voorspellingsmodel, gebaseer op die beheer-volume benadering, is ontwikkel om die tempo van bevriesing en ontdooiing van vakuumverpakte heel volstruisspiere te voorspel. Die model het tempo van bevriesing en ontdooiing met groter akkuraatheid as die bestaande modelle voorspel en kan suksesvol gebruik word in die bestuur van slagpale. Verder navorsing is onderneem om ondersoek in te stel na die effek van die tempo van bevriesing en ontdooiing op die kwaliteit van die bevrore-ontdooide volstruisvleis tydens berging by ±4°C. Die invloed van die kombinasie van vyf bevriesingstempo’s (FR (tydsverloop 0°C tot -7°C): 1, 2, 4, 8, 24 h) met vyf ontdooiingstempo’s (OT (tydsverloop -7°C to 0°C): 1.5, 3, 6.5, 14, 21 h) is ondersoek. Die resultate het getoon dat ontdooiingstempo geen beduidende invloed op enige van die kwaliteit kriteria, insluitend ontdooiingsverlies, gehad het nie. Bevriesingtempo het egter ‘n groot rol ten opsigte van yskristalvorming gespeel. Teen ‘n kenmerkende bevriesingstempo van een uur (FR_1h) was slegs intrasellulêre yskristalle waargeneem dwarsdeur die M. femorotibialis wat gelei het tot die laagste ontdooiingsverlies (2.57 %). Die ander bevriesingstempo’s, d.i. FR_2h, FR_4h en FR_8h, het gelei tot die vorming van meestal ekstrasellulêre yskristalle. Bevriesingstempo’s van FR_2h en FR_8h het beduidende dehidrasie van die spiervesels en vervorming van die spiervesel matriks tot gevolg gehad, wat tot verhoogde oksidasie gelei het. ‘n Bevriesingstempo van FR_24h (d.i. kommersieële tempo), het gelei tot die vorming van yskolomme van die oppervlak na die middelpunt van die spier, wat gevolglik die grootste ontdooiingsverlies (6.24%) tot gevolg gehad het. ‘n Bevriesingstempo van vier ure (FR_4h) is bestempel as die mees geskikte bevriesings tempo as gevolg van ‘n matige ontdooiingsverlies (3.93%), drupverlies, lae kookverlies, goeie kleur stabiliteit en uiters lae lipiedoksidasie te verseker. Die FR_4h bevriesingstempo is haalbare in die bedryf. Indien dit geïmplementeer word, sal dit waarskynlik die deurset van die slagpalesiklus asook die kostedoeltreffendheid van die volstruisbedryf vebeter, deur die vermindering van ontdooiingsverlies en verbetering van die algehele kwalitiet van die vleis.