Predicting intramuscular fat in beef longissimus muscle from speed of sound.

The ultrasonic A-mode method was investigated for intramuscular fat measurement of beef. Cubes of meat samples that had different marbling scores were used as specimens. Ultrasonic speed decreased with increasing fat concentration. The correlation coefficient was -.82 (P < .05). Conversely, the correlation coefficient between visual marbling score and fat concentration was .70 (P < .05). Quantitatively, from the first derivative of a nonlinear function, it was concluded that the speed decreased at a rate of 2.69 m/(s-% fat) as a function of intramuscular fat. A nonlinear regression model to predict intramuscular fat content in beef was developed as follows: percentage of fat concentration = 7132.1574-9.1222 x (speed) + 2.91803 x 10(-3) x (speed)2 (R2 = .81). The nonlinear model was capable of predicting intramuscular fat concentration with 90% accuracy (> 8% fat) and 76.4% accuracy (< 8% fat), respectively (P < .001).

Measuring intramuscular fat in beef with ultrasonic frequency analysis.

Frequency analysis of Fourier spectra from ultrasonic signals was used for predicting intramuscular fat content of beef tissue. The most significant parameter in the frequency domain for predicting intramuscular fat concentration in beef was the number of local maxima. It represents the discontinuity of the Fourier spectrum caused by inhomogeneous fat concentrations in the longissimus muscle, which had the correlation coefficient .89 (P < .05) when a 2.25-MHz shear probe was used. The optimum frequency for predicting the amount of intramuscular fat content in the longissimus muscle was found to be 1.92 MHz. A multivariate regression model was developed using parameters in the frequency domain as follows: percentage of fat concentration = 1.790 - 2.373x (lower frequency) + .049x (bandwidth) + 1.178x (local maxima) (R2 = .82). Validation demonstrated that the multivariate model in the frequency domain was capable of predicting intramuscular fat concentration with an average of 1.17 percentage of fat error (P < .05). The multivariate model was most appropriate for predicting intramuscular fat below 4%. The mean accuracy of the model in the frequency domain was approximately 79%.

Elastography of beef muscle.

Elastography, a technique that uses ultrasonic pulses to track the internal displacements of small tissue elements in response to an externally applied stress, has been applied to beef muscle. Beef longissimus (1 day post mortem) and semimembranosus (5 days post mortem) muscles were obtained from A maturity beef carcasses. Samples were vacuum-packaged and frozen to -20°C. For elastography measurements, muscles were equilibrated to a constant temperature (30° C± 0·5) in a water tank. Custom transmitters and receivers were used in conjunction with a 2·25 MHz medical transducer. The transducer was driven by a 286 PC, and the radio-frequency echoes digitized at 50 MHz and 8 bits. The pre- and post- compression echo trains (A-lines) were subjected to cross-correlation analysis. Visual interpretation of beef elastograms demonstrate circular areas of relatively inelastic tissues and smaller, banding areas of elastic tissues in the cross-section of beef longissimus muscle. The dark inelastic areas from the elastograms may be related to myofibrilar areas from the same muscle sections; the light, elastic band areas from the elastograms may be related to perimysiaal connective tissue or intramuscular fat. Fatty septa and a calcified abscess could be easily identified on the elastogram. These preliminary results demonstrate that elastography may have potential as a non-intrusive method of visualizing tissue components of beef muscle.

Principles of ultrasound and measurement of intramuscular fat.

A review of basic engineering concepts of ultrasound is presented for the layperson with implications toward the use of ultrasound on beef animals. The use of ultrasound for determining quality traits such as percentage of intramuscular fat is discussed in detail. Results of both A-mode and B-mode preliminary investigations are presented. Preliminary results show that intramuscular fat may be predicted using an A-mode transducer coupled with frequency analysis.

The role of instrument grading in a beef value-based marketing system.

A functional value-based marketing system must have a means of identifying the value of individual animals or carcasses. The U.S. beef industry has had a strong interest in instrument grading for the past 11 yr. With the major shift toward a value-based system of trading (carcass), the beef industry has defined its needs for an instrument to assess value. Ultrasound seems to be the technology with the greatest chance of success. This paper outlines the history of instrument grading and industry's progress and plans in this area.