Mike F. North

The protective effect of electrical stimulation and wrapping on beef tenderness at high pre rigor temperatures.

A three factorial experimental design involving electrical stimulation (ES/NES), wrapping (wrapped/unwrapped) and pre rigor temperature (15°C or 35°C) was applied to 70 beef M. longissimus lumborum muscles to obtain a wide variation in shear force and drip loss. The shear force of all treatment groups decreased during ageing. As anticipated, wrapping and electrical stimulation had positive effects on shear force. However, high pre rigor temperature (35°C) did not result in higher shear force values if the muscles were electrically stimulated, wrapped or both. The results suggested that electrical stimulation protects against the negative effects of high pre rigor temperatures. The drip loss of all treatment groups increased during ageing in a manner that was unrelated to treatment but was correlated to tenderness (r(2)=0.70; p<0.0001). It was concluded that the application of electrical stimulation, whatever the pre rigor temperature, protects beef from toughening through the prevention of rigor shortening and the avoidance of inhibition of ageing enzymes.

Temporal, biochemical and structural factors that influence beef quality measurement using near infrared spectroscopy

This study included simultaneously measured pre and post-rigor meat quality indicators and attributes, using near infrared (NIR) spectroscopy and reference methods, to understand the temporal, biochemical and structural factors that influence beef quality and use this knowledge to build calibrations for measurement of meat quality using NIR. Eighty beef M. longissimus lumborum (LL) were measured from early pre-rigor (pH, glycogen concentration, and temperature) through to completion of post-rigor ageing (pH, shear force, and water holding capacity (WHC)). To create a range in the attributes, the LLs were subjected to various pre-rigor treatments, including electrical stimulation, restraint wrapping and cooling temperature (5°C, 15°C, or 35°C). Alongside the reference quality measurements and throughout the pre and post-rigor period, the LLs were measured with a diode array NIR spectroscopy system. NIR reflectance measurements were shown to be correlated to reference measurements of pre and post-rigor pH (R(validation)(2)=0.84), pre-rigor glycogen content (R(validation)(2)=0.70), post-rigor shear force (R(validation)(2)=0.58) and post-rigor WHC (R(validation)(2)=0.68). The shape of the NIR and reference plots over time and the ability of NIR to correctly measure differences in treatments indicated that NIR was not merely measuring changes that occur over time, but was measuring specific biochemical and physical changes, most likely changes in glycolytic metabolites, muscle shortening and/or proteolysis. Accounting for the reference method variance showed NIR measurement accuracy to be as good as or slightly better than that of the reference method.

The initial freezing point temperature of beef rises with the rise in pH: A short communication

This study tested the hypothesis that the initial freezing point temperature of meat is affected by pH. Sixty four bovine M. longissimus thoracis et lumborum were classified into two ultimate pH groups: low (<5.8) and high pH (>6.2) and their cooling and freezing point temperatures were determined. The initial freezing temperatures for beef ranged from -0.9 to -1.5°C (∆=0.6°C) with the higher and lower temperatures associated with high and low ultimate pH respectively. There was a significant correlation (r=+0.73, P<0.01) between beef pH and freezing point temperature in the present study. The outcome of this study has implications for the meat industry where evidence of freezing (ice formation) in a shipment as a result of high pH meat could result in a container load of valuable chilled product being downgraded to a lower value frozen product.

Near infrared spectroscopy as an on-line method to quantitatively determine glycogen and predict ultimate pH in pre rigor bovine M. longissimus dorsi.

The potential of near infrared (NIR) spectroscopy as an on-line method to quantify glycogen and predict ultimate pH (pH(u)) of pre rigor beef M. longissimus dorsi (LD) was assessed. NIR spectra (538 to 1677 nm) of pre rigor LD from steers, cows and bulls were collected early post mortem and measurements were made for pre rigor glycogen concentration and pH(u). Spectral and measured data were combined to develop models to quantify glycogen and predict the pH(u) of pre rigor LD. NIR spectra and pre rigor predicted values obtained from quantitative models were shown to be poorly correlated against glycogen and pH(u) (r(2)=0.23 and 0.20, respectively). Qualitative models developed to categorize each muscle according to their pH(u) were able to correctly categorize 42% of high pH(u) samples. Optimum qualitative and quantitative models derived from NIR spectra found low correlation between predicted values and reference measurements.