G. K. Searcy

Pyruvate Kinase Activity as an Indicator of Temperature Attained During Cooking of Cured Pork

Muscle pyruvate kinase (PYK) activity was established as a biochemical indicator of temperature attained during cooking in both a model system and a commercial-type pullman-style canned cured pork product. Water extract (model system) or pressed-out meat juice (commercial-type pullman-style canned cured pork) was incubated (37°C up to 40 min) with reagent containing adenosine diphosphate, phosphoenolpyruvic acid and NADH. Lactate dehydrogenase (LDH) necessary for the reaction is provided by the muscle extract or meat juice. When muscle PYK activity is present, NADH is oxidized resulting in a loss of fluorescence (reaction mixture spots on filter paper viewed under long-wave ultraviolet light). Model system results showed high PYK activity (no fluorescence) remained in samples heated to 67.7°C. PYK activity progressively declined in samples heated to 68.3°C and 68.9°C. No PYK activity was detected in samples heated to 69.5°C or 70°C. Canned product attaining a core temperature of 62.9°C had high PYK activity. PYK activity progressively declined in product heated to 65.6°C and 68.6°C. Essentially no PYK activity was detected from product processed to 69.9°C.

Variability in Residual Myoglobin Content and Glutamic Oxaloacetic Transaminase (GOT) Activity in Cooked Bovine Semimembranosus Tissue as Related to Temperature of Cooking Media above End-point Temperature and Sample Size

The variables, sample size and temperature of cooking media, were tested to determine their influence on myoglobin content and glutamic oxaloacetic transaminase (GOT) activities in bovine semimembranosus tissue thermally processed in a model heat treatment system. Data were obtained from 2.9 and 5.5 × 8.0 cm samples that were thermally processed to end-point temperatures (EPTs) of 62.8, 71.1 and 79.4°C in a water bath that exceeded EPTs by 2 and 20°C. Myoglobin denaturation differed (P < 0.05) by EPTs within samples, by sample size at the specified EPTs and by temperature of the heating media used to attain the EPTs within sample sizes. Similar variations at this probability level were observed in the analyses for residual GOT activities of the samples. Data indicate the inadequacies of analysis of these parameters in model systems that do not duplicate the actual process being evaluated.

Evaluation of Creatine Phosphokinase Activity as a Means of Determining Cooking End-Point Temperature

The influence of cooking end-point temperatures (EPTs) of 62.8, 66.7, 67.8, 68.9, 70.0, 71.1, 73.9, and 76.7°C on residual creatine phosphokinase (CPK) activity in laboratory prepared model systems of ground chicken and turkey breast meat was determined. CPK activity was also assayed in commercially prepared chicken, turkey, and meat products using a Sigma #661 CPK test kit. Three tenths milliliter of 0.9% saline extracts obtained from the chicken, turkey, and meat products was substituted for 0.3 ml serum specified in the test kit procedure. For the model samples, there was a marked decrease in CPK activity as EPT increased from 66.7 to 76.7°C; however, model samples heated to 76.7°C did retain low amounts of CPK activity. In general, very low levels of CPK were found in commercially prepared chicken and turkey products (0 to 10.6 Sigma units/ml). Results of CPK activity in commercially prepared meat products would indicate that the test is product dependent, with values ranging from zero for beef franks to 258 Sigma units/ml for hard salami. Thus, while CPK activity may be useful for detecting cooking EPT for quality control purposes, it should not be used as a regulatory procedure where experience with the specific product is not available.

Colour values of cooked top-round beef juices as affected by endpoint temperatures, frozen storage of cooked samples and storage of expressed juices

Juices from beef semimembranosus/adductor tissue, cooked to endpoint temperatures (EPTs) of 76, 78, 80, 82 and 84°C in a model heat-treating system, were evaluated for changes in CIELAB L*a*b*, chroma (C) and hue angle (H) values before and after storage of the cooked meat at -20°C for 3 weeks and after storage of the expressed juices under N 2 at 3°C for 72 h. Increases in EPTs altered all colour values of the juices. Lightness (L*) increased while yellowness (b*) decreased; redness (a*) and C decreased progressively while H increased toward the vertical axis. Storage of the expressed juices at 3°C under N 2 did not inhibit changes in a*, b*, C and H values. Regression coefficients of changes in relation to EPTs and time of storage of the expressed juices under N 2 were established. Storage of the cooked meats for 3 weeks at -20°C did not change any of the colour values of the juices. These data indicate that evaluations of cooked beef for doneness by colour of expressed juices must be performed immediately after expression of the juices before oxidation of the myoglobin pigments occurs. Storage of cooked meat at -20°C does not alter the colour of the juices, therefore, valid assays for doneness of meat in relation to juice colour can be made after frozen storage.

Glutamic-Oxaloacetic Transaminase Activity in Commercially Processed Chicken: An Indicator of Product End-Point Temperature†

Residual glutamic-oxaloacetic transminase (GOT) activity in laboratory-prepared samples of white and dark chicken meat heat treated to end-point temperatures (EPTs) of 70 to 75°C were determined. Declines in activity with increasing EPTs occurred in both tissue types; activities were significantly higher (P < 0.05) in dark meat samples at all EPTs except 75°C. Regression coefficients of GOT activities on EPTs of the laboratory prepares sampled were rearranged to estimate EPTs for poultry products obtained from a commercial processing plant. Desired EPTs of the commercial products were 71 and 74°C for white and dark meat, respectively. Product EPTs estimated by measurement of residual GOT activities were 74 to 75°C. Measurement of residual GOT activity appears to be a rapid, accurate means to estimate EPTs in commercially produced poultry products of uniform size and thickness.

Glutamic-Oxaloacetic Transaminase Activity: A Potential End-Point-Temperature Indicator for Imported Cooked Beef†

Glutamic-oxaloacetic transaminase (GOT) activities in thermally processed beef samples were determined with a diagnostic test kit (no. 505P, Transaminases ALT/GPT and AST/GOT, Sigma Chemical Co.) procedure for possible use as indicators of cooking end-point temperatures (EPTs) between 71.1 and 82.2°C. GOT activity in the beef samples decreased curvilinearly with increasing EPTs. Activity was 3,450, 120, and 6 Sigma-Frankel units/ml (SFUs/ml) at 71.1, 75.6, and 82.2°C, respectively; a reduction of 99.8%. GOT values at 78.9,79.4, and 80.0°C, the critical range of EPTs in evaluating beef logs imported from South America, were 31, 17, and 14 SFUs/ml, respectively. Values within this range of temperatures differed significantly (P < 0.05); we suggest that residual GOT activity may be used as an EPT indicator for imported cooked beef products.