Accurate and reliable measurement of meat quality is essential for the Australian beef industry to remain competitive in both the domestic and export markets. Recent developments of the resonator technique have lead to the commercial availability of the High Resolution Ultrasound Spectroscope (HR-US). This research project was designed to assess the potential of HR-US for the analysis of post-mortem bovine muscle. This was accomplished by; 1) establishing a suitable measurement protocol that considered sources of variability, 2) the effects of post-mortem aging on HR-US parameters, 3) analysis of thermal related changes that occur in muscle, and extracted connective tissue during heating, and 4) the use of HR-US for the measurement of the intramuscular fat. A procedure for the measurement of bovine muscle with HR-US was established. Briefly, an external semisolid cell was used as the measurement cell. The frequency range of 2000 KHz to 3000 KHz was selected as the most suitable for whole muscle analysis and all five resonance peaks within this range were analysed and used to obtain velocity and attenuation values of the meat sample. Water was used as the reference media, and measurements were conducted at 250C. Changes were made to this method during experimental work depending on the sample being run and the objectives of the study. The measurement protocol was shown to be repeatable. Factors likely to cause variation in measurements of the samples, such as water loss and freeze-thaw, were also considered when developing the operational parameters of the study. High resolution ultrasound spectroscopy was applied to measure the post-mortem changes that occur in bovine muscle. Using two muscle types, Semitendinosus and Psoas major, significant changes were observed in HR-US parameters with ageing. Significant increases in the acoustic impedance of bovine muscle with increased ageing time were attributed to degradation of the muscle structure. This was confirmed in transmission electron microscopy images where clear disruption the myofibillar structure was apparent in the muscle at 21 days post-mortem.In localised regions the Z bands and the adjoining actin fibres were totally degraded. Water loss from the muscle system had a significant influence on HR-US measurements. Thermal related changes that occur in whole bovine muscle and in isolated intramuscular connective tissue were observed with HR-US. Heat induced changes were identified in whole muscles and included the melting of the fat within samples at 48oC, coagulation of sarcoplasmic proteins between 450C and 55oC, and the shrinkage of collagen fibres at 630C. An 80% reduction in the attenuating properties of extracted connective ageing in buffer solution was observed within the first 5 days. This is attributed to the degradation of proteoglycans and the resulting disassociation of collagen fibrils. Structural changes occurring in extracted connective tissue were observed with TEM. HR-US measurements proved to be highly sensitive to identifying temperatures at which transitions occurred. Unfolding of the triple helix structure of collagen was identified in velocity transitions between 59°C and 63oC. HR-US results suggested a greater sensitivity to thermal related changes in extracted intramuscular connective tissue when compared with differential scanning calorimeter results. An increase in temperature was observed for thermal denaturation of collagen with ageing, however a reduction was also observed in the temperature range at which the denaturation process occurred. Temperature ramps conducted on extracted intramuscular bovine showed a reduction in velocity from 1613.1m/s at 250C to 1343.1 m/s at 900C equalling an overall reduction in velocity of 270m/s. A transition in the velocity trend seen at 46°C indicates the majority of the triglycerides are melted (or in liquid state) above this temperature. Results are confirmed with differential scanning calorimeter thermogram. HR-US measurements showed high sensitivity to increasing concentration of bovine fat in prepared emulsions with an adjusted R2 99.46% for velocity measurements taken at 5100 kHz. Attenuation values at 8100 kHz also showed a strong linear response to increasing fat concentration in the emulsion (R2 98.77). The use of HR-US for the measurement of intramuscular bovine fat demonstrated a high sensitivity to extracted bovine fat in prepared emulsions. An increase in the intramuscular fat content of whole bovine muscles resulted in a reduction in the velocity measurements and an increase in the attenuation of the ultrasonic signal. This provides the basis for potential method for the prediction intramuscular fat in bovine muscle. The present studies have highlighted the complexities of investigations relating to meat quality and have demonstrated the diversity of data required to assess quality. Only when comprehensive data are available, can we hope to accurately determine meat quality and predict how it will vary with changes in animal production and meat processing.
| Identifer | oai:union.ndltd.org:ADTP/254187 |
| Creators | Timothy Sweet |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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