The Relationship between Meat Color (CIE L* and a*), Myoglobin Content, and Their Influence on Muscle Fiber Characteristics and Pork Quality

The aim of this study was to investigate the histochemical parameters of muscle fibers, and to estimate the correlation of muscle fiber characteristic to postmortem metabolic rate and meat quality traits in pigs. A total of 231 crossbred pigs were evaluated. Samples of the longissimus dorsi muscle were taken to evaluate the histochemical characteristics, postmortem metabolic rate and meat quality. Fiber type composition was mainly related to postmortem metabolic rate and meat quality traits among various muscle fiber characteristics. The percentage of type IIb fiber was negatively related to pH(45min) (r=-0.33) and positively to R-value (r=0.32). Drip loss was negatively related to fiber area percentages of type I and IIa (r=-0.25 and -0.26, respectively) and positively related to type IIb percentage (r=0.39). A similar tendency was found between lightness and fiber area percentage. In conclusion, increasing the percentage of type IIb fiber is related to increasing the postmortem metabolic rate, and is related to the deterioration of meat quality.

In order to investigate the relationship of sarcoplasmic and myofibrillar protein solubility to colour and water-holding capacity (WHC) in pork, 60 loins were selected to represent the quality classes: PSE (pale, soft, exudative), RSE (reddish-pink, soft, exudative), RFN (reddish-pink, firm, non-exudative) and DFD (dark, firm, dry). PSE samples exhibited lower (p<0.05) protein solubility (sarcoplasmic, myofibrillar and total) compared to the other quality classes. RSE samples exhibited lower (p<0.05) sarcoplasmic protein solubility compared to DFD samples. RSE, RFN and DFD samples had similar myofibrillar and total protein solubilities. Sarcoplasmic protein solubility explained 71% of the variation in lightness with a linear decrease in L* value. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) gels of the sarcoplasmic and myofibrillar samples distinctly showed the association of some sarcoplasmic proteins with the myofibrillar protein fractions in PSE and RSE samples. The sarcoplasmic proteins which precipitated were phosphorylase, creatine kinase, triose phosphate isomerase and myokinase for PSE and phosphorylase for RSE samples. Pork colour is highly correlated with precipitation of sarcoplasmic proteins while WHC is affected by denaturation of myofibrillar proteins (PSE samples) and lower ultimate pH (PSE and RSE samples).