Effect of pre-slaughter physiological conditions on the oxidative stability of colour and lipid during chill storage of pork.

The physiological condition of the live animal was found to significantly affect colour, lipid oxidation and water holding capacity of chill stored pork chops (M. Longissimus dorsi) in a study, where various pre-slaughter conditions were achieved by the following four treatments: (A) control; (B) subjected to treadmill exercise immediately prior to stunning; (C) given epinephrine injection 15 h prior to slaughter; and (D) given epinephrine injection 15 h before slaughter and further subjected to treadmill exercise immediately before stunning. The treatments resulted in variations in energy metabolites (glycogen, lactate, creatine phosphate, ATP) and ultimate pH (pH(u)), with the lowest pH(u) in chops from treatments A and B, and in significantly different tristimulus colour L(∗)-, a(∗)- and b(∗)-parameters, although the effect of treatment on colour was not consistent during the chill storage period of 6 days. Overall, chops from treatments A and B had significantly higher L(∗)- and b(∗)-values (were paler and less blue) than chops from C and D during storage under conditions typical for retail trade. The initial a(∗)-values were higher (redder) in chops from treatments A and B, but the colour, as judged by the a(∗)-values, was less stable in meat from these treatments compared with treatments C and D. Lipid oxidation, evaluated by thiobarbituric acid reactive substances (TBARS) in the fresh meat, and drip loss, measured after 6 days of storage, were both significantly higher in chops from treatments A and B compared to chops obtained from treatments C and D. Statistical analysis relating the pH and the level of various energy metabolites post-mortem in the individual animals to the measured quality parameters, revealed that pH(u) was the most important factor affecting product quality. In conclusion, over all product quality depends on obtaining a pH(u) in the narrow range where both meat quality parameters such as colour, lipid oxidation and drip loss as well as microbiological aspects have to be considered.