30C-5 |
Determinants of ultimate pH of pork |
R. L. J. M. VAN LAACK1, J. Yang, and E. Spencer. (1) Department of Food Science and Technology, University of Tennessee, P.O. Box 1071, Knoxville, TN 37901-1071 Rate and extent of post-mortem pH decline are the main determinants of pork quality. For pork with high water-holding capacity and reddish pink color, an ultimate pH (pHu) of >5.7 is desirable. At pH>5.7, the risk for PSE (pale, soft, exudative) and RSE (red, soft, exudative) quality is minimal. Before we can produce pork with a pHu>5.7, we need to know what factors determine pHu. We analyzed the contribution of substrate level (glycogen and creatine phosphate), buffering capacity and level of the enzymes AMP-deaminase and glycogen phosphorylase to the pHu of pork longissimus muscle. We slaughtered sixty pigs, 10 each of 6 different halothane negative lines. Within 5 min after stunning, the loin was sampled for analysis of various metabolites and activity of the two enzymes (AMP deaminase and phosphorylase) that have been reported to influence pHu. At 18-24 h post mortem, we measured pHu, color L*-value (measure for lightness), drip loss and buffering capacity. Based upon post-mortem pH decline, L*-value and drip loss, 7 pigs were excluded from analysis. These pigs had an extremely fast glycolysis which resulted in PSE and enzyme denaturation, thus a 5-minute sample would not approximate glycolytic makeup of the typical pig at slaughter. Glycolytic potential (a measure of glycogen concentration at time of slaughter), phosphorylase a, buffering capacity and AMP deaminase correlated with pHu (P<0.05). Glycolytic potential explained 37% of the differences in pHu (higher glycolytic potential– lower pHu). A higher phosphorylase a activity correlated with a lower pHu (r=-0.47) and higher buffering capacity was associated with a higher pHu (r=-0.43). AMP deaminase activity explained about 10% of the differences in pHu. When combining several factors, phosphorylase a and glycolytic potential explained 47% of the variation in pHu. Factors controlling the residual variation remain undetermined.
Session 30C, Muscle Foods: Tenderness, Quality, Processing, Marination, Oxidation, and Shelf-Life
|