The effect of varying the degrees of β-receptor stimulation on the activity of the calpain - calpastatin system at slaughter in porcine longissimus dorsi

Despite efforts to standardise breeding, nutrition and husbandry regimes, consumer studies indicate that 17% of all loin chops sold in the UK are unacceptable in terms of toughness and dryness (Warkup et al., 1995). Recent evidence suggests that this unaccountable variability may be at least partly due to changes in the calpain-calpastatin proteolytic system around the time of slaughter, stimulated by changes in the circulating levels of the natural β-agonist adrenaline (Sensky et al., 1996). An increase in calpastatin, the inhibitory component of the system, at slaughter has also been shown to be associated with reduced degrees of tenderisation (Koohmaraie, 1992, Sensky et al., 1996b). Variation in the degree of β-receptor stimulation close to slaughter should therefore correlate with calpastatin levels at slaughter. This study aimed to investigate the validity of this claim.The diet of 30 female Landrace x Large White pigs (67 ± 1 kg) was supplemented with either 2 or 20 ppm nadolol, a β-antagonist, or clenbuterol, a β-agonist, 16 h before slaughter, giving 5 groups of 6 pigs, including controls (no supplement), with differing degrees of β-receptor stimulation, ranging from low (20 ppm nadolol) to high (20 ppm clenbuterol). Calpain and calpastatin activities were measured in samples of longissimus dorsi (LD) taken immediately after slaughter using chromatographic and fluorimetric techniques (Sensky et al., 1996b).