Masters Theses

Jun Yang

Date of Award

12-2000

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Riëtte van Laack

Committee Members

Sharon L. Melton, Clark J. Brekke

Abstract

Annually, millions of dollars are lost due to the variation in meat quality. Ultimate pH (pHu), one of the most important quality traits, has a great influence on water holding capacity and meat color. The National Pork Producers Council (NPPC) quality solutions team suggested an ultimate pH within the range of 5.6-5.9 as optimum. The project of the study was to evaluate the possible determinants of ultimate pH. The effects of glycolytic potential (GP), creatine phosphate (CP), buffering capacity (BFC) and titratable acidity (TA), and the enzyme activities of phosphorylase (GPa) and AMP deaminase (AMPD) were investigated. Sixty pigs of 6 different genetic lines were used. At 5 min post mortem, the longissimus muscle was sampled for analysis of various metabolites (CP, GP, lactate) and enzyme activities. The meat quality characteristics (pHu, color (L*-value), drip loss and filter paper wetness), BFC and TA were measured at 18-24 hr post mortem. The pigs were classified into PSE (Pale, Soft and Exudative) and 'normal' based on their physical and biochemical characteristics. Seven pigs were identified as PSE meat (L*-value > 58 and drip loss > 5%). The remaining 53 were normal. No dark, firm and dry meat (DFD; pHu > 6.0) was found. The correlations among GP, GPa, BFC and AMPD were significant. Glycolytic potential, where all components potentially can be converted to lactate, explained 42% of the variation in pHu; increased glycolytic potential was associated with a lower pHu. The GPa explained 28% of the difference in pHu; a high activity of GPa was associated with a lower pHu. A high BFC decreased pHu (r= - 0.43). The activity of AMP deaminase explained about 10% of the difference in pHu; pHu increased with an increased AMPD. The best statistic model for predicting pHu was developed as: pHu= 5.75 - 1.21X10-3*GP - 3.14X10-5 * GPa*GPa. This model explained 47% of variation of pHu. Only when we know what determines ultimate pH, can we produce animals with a specific pHu and, thus, with a consistent quality.

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