Lactate dehydrogenase activity in bovine muscle as a means of determining heating endpoint

Abstract

Influence of pH, salt, phosphate, cooking temperature, muscle variation, carcass sex and maturity on lactate dehydrogenase (LDH, E.C. 1.1.1.27) activity in bovine tissue slurries was investigated. LDH activity declined sharply as temperature neared 63°C at pH 5.6 and 6.4, but no activity was detected at pH 4.8. As salt and phosphate concentrations increased, LDH activity decreased. LDH activity varied greatly from muscle to muscle. Carcasses did not differ in LDH activity by sex, but showed a decrease in activity as maturity increased. LDH activity declined significantly when bovine Semimembranosus (SM) slurries were heated to 63° and 66°C. LDH5 was the predominant isoenzyme in the SM, Infraspinatus and Longissimus dorsi, accounting for 77, 6 6 and 8 6 % of the total activity, respectively. LDH activity was lower (P<0.05) in tissue from animals > 14 yr, but LDH5 remained the predominant isoenzyme. LDH activity significantly decreased in bovine SM tissue when whole muscle roasts were brine pumped and oven cooked to a final internal temperature of 61.7°C. Fluorescent and colorimetric tests for LDH activity, adaptable to a rapid assay, were successfully used to monitor heating endpoint in comparison to the currently utilized USDA-FSIS method.