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 has potential as a determinant of the minimum heating endpoint in precooked beef and a rapid analytical test could be developed.

MATERIALS & METHODSFive levels (0, 5, 10, 15, 20%) of partially defatted chopped beef (PDCB) were substituted for lean in fermented beef stick sausage to evaluate changes over a 90 day period (24°C). Replacement of 0, 5, 10, 15, and 20% of the lean with PDCB did not affect percentage of fat, moisture, protein, moisture:protein ratio, or a, of the final product. TBA values were different (PcO.05) between storage periods, but were all lower than those associated with oxidative rancidity. Warner-Bratzler shear values increased incrementally with increasing PDCB but were still within acceptable limits. Sensory profiles indicated that concentration of PDCB in the formulation had no effect on aroma, mouthfeel, taste, or texture of the product over storage time. MaterialsFresh, lean beef trimmings (90% lean) and beef fat trim (60% fat) from the flank, chuck, and plate were obtained from the Rosenthal Meat Science and Technology Center at Texas A&M University. Frozen chips of partially defatted chopped beef (Beef Products, Inc., Austin, TX) were received in a frozen state and stored frozen ( -23°C) 2 months, until used.

Lactate dehydrogenase (LDH, E.C. 1.1.1.27) activity, specifically LDH5 isoenzyme, declined significantly when bovine Semimembranosus (SM) slurries were heated from 57Њ to 66ЊC. When SM whole muscle roasts were brine pumped and oven-cooked, total LDH and specific activities declined proportionately from 57Њ to 63ЊC resulting in almost no activity at 63Њ ‫ע‬ 0.5ЊC. LDH activities were consistently higher in younger cattle and lower in older cattle for SM, Infraspinatus (IN) and Longissimus dorsi (LD) muscles and were lowest overall in the IN. LDH colorimetric and fluorescent assays were more accurate indicators for predicting beef roast heating temperature endpoints between 60Њ and 63ЊC than the USDA-FSIS method.