Comparison of iodine value equations among pork carcass fat depots of immunologically castrated pigs

Abstract

cells transformed by a pET(21) plasmid containing the Shp gene and purified. Ability of apoShp to remove hemin from pork metHb was spectrophotometrically determined (n = 2) in solution by observing absorbance shifts from 405 nm (metHb peak) to 418 nm (holoShp peak) during incubation at 0.2 °C and pH 5.9. To investigate the significance of residual Hb in promoting lipid oxidation in pork muscle, the Semitendinosus was selected as a model muscle. The muscle was trimmed to select the red portion, ground with a 5 mm plate, and minced in a food processor. Heme content of the mince was determined by acid–acetone extraction. Lipid oxidation in stored mince (0.2 °C, pH 5.9, n = 2) with and without added apoShp was investigated by thiobarbituric acid reactive substances (TBARS) measurement. Statistical analysis employed the MIXED procedure of the SAS system. Results: Promotion of lipid oxidation in the mince was affected by the presence of 1.5% NaCl at 0.2 °C and pH 5.9. The 1.5% NaCl treatment achieved a significant increase in TBARS formation over the 0% treatment (P=0.0005). By 241 h of storage, TBARS in the 1.5% NaCl treatment reached 48.45 ± 2.45 μmol TBARS/kg mince, while TBARS in the 0% NaCl treatment reached 0.049 ± 0.069 μmol TBARS/kg mince, representing a 989-fold increase in TBARS formation (P b 0.0001). To determine the significance of residual Hb in promoting lipid oxidation in the mince, effect of a 2.5-fold excess of apoShp over total heme pigment content on TBARS formation in the mince was investigated in the presence of 1.5% NaCl. ApoShp significantly inhibited TBARS formation (P= 0.0019). By 131 h of storage, TBARS in the apoShp treatment reached 0.490 ± 0.690 μmol TBARS/kg mince, while TBARS in the apoShp-free treatment reached 9.129 ± 0.439 μmol TBARS/kg mince, representing a 95% inhibition of TBARS formation (P b 0.0001). To determine the ability of apoShp to remove hemin from pork metHb, a 4-fold excess of apoShp over metHb was incubated with pork metHb, in the presence of 1.5% NaCl. Evidenced by a shift in absorbance from 405 nm to 418 nm, apoShp removed increasing quantities of hemin from pork metHb over 91 h. Conclusion: These data suggest Hb, not Mb, as the primary promoter of lipid oxidation in pork Semitendinosus muscle, and reinforce the importance of residual blood in postmortem muscle as a target for antioxidant strategies.