ABSTRACT
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.
ABSTRACT
A new quantitative f1uorometric assay was used to determine poultry-muscle acid phosphatase (ACP) activity at five end-point temperatures (EPTs). Nonfrozen or frozen ground broiler and turkey breast and turkey dark meat (16 9) were packed in glass tubes (25 ×150mm) and heated to 62.8, 65.6, 68.3, 71.1 and 73.9°C in a water bath set 1.5°C above target EPT. After heating, samples were removed and immediately chilled (2-3°C). A 75 µl portion of an aqueous meat extract (1 meat/2 H2O wt/wt) was added to 2.0 ml ACP substrate and the kinetic increase in fluorescence monitored at 38°C. The experiment was replicated three times. A curvilinear decrease in mean (N = 12) ACP activity occurred within each muscle type. Although freezing before cooking lowered ACP activity, it was not different (P>.05) from that of nonfrozen meat. Acid phosphatase activity (mU/kg) means (N = 12) with standard errors for EPTs between 68.3 and 71.1°C for broiler and turkey breast and turkey dark meat were as follows: 9270 ± 873 and 5548 ± 562; 9313 ± 665 and 6808 ± 521; and 4821 ± 398 and 3370 ± 281, respectively. This procedure provides a rapid (3 min instrument time), sensitive analytical method for quality-assurance process-control technicians or regulatory analysts to monitor EPT in cooked poultry.
ABSTRACT
Protein solubility loss as a result of heat denaturation/coaguiation was followed by a ratio of extractable biuret positive compounds (EBPR). Extracts of water-soluble proteins were evaluated by isoelectric focusing (IEF) on polyacrylamide gels. Four heat treatments (60°C, 62.8°C, 65.6°C and 68.8°C) were employed in processing canned (No. 300×407) cured pork. Center cores from canned samples were ground for water soluble protein extraction utilizing a 1:3.3 meat-to-water ratio by high-speed blending (Sorvall Omni-mixer) for 1 min at 0-2°C, centrifuging 10 min at 27,000 ×g at 0-2°C and filtering (0.45-µa.m) with vacuum assist. Eight ml of the clear extract was re-heated in a glass tube for 15 min at 70°C, removed, and chilled (0-2°C) immediately. Coagulum was removed by filtration. EBPR was calculated from mg of protein/ml of initial muscle extract divided by mg of protein/ml of reheated extract for each temperature treatment. EBPR values were 1.75, 1.24, 1.13, and 1.10, respectively. Using 70°C as the critical temperature, an upper 95% confidence limit EBPR value of 1.12 was calculated. Portions of protein extract were isoelectrofocused on thin layer (0.8 mm) low concentration (5% monomer) polyacrylamide gels (pH gradient 3-10). IEF gels generally showed resolution of 12 to 23 protein bands in the muscle extracts, depending upon temperature treatment. Certain bands with apparent isoelectric points (pis) ranging from 7.4 to 8.5 decreased in staining intensity (silver stain) as temperature increased. The general protein separation profiles correlated with decreasing EBPR values as temperature increased.
ABSTRACT
Ground pork longissimus or beef semimembranosus muscle was heated in stoppered glass tubes in a controlled temperature bath at 60, 65, 67.5, 70, or 75°C and held for 0, 7.5, 15 or 30 min after the sample reached the desired internal temperature, removed, and cooled (0-2°C) immediately. Heated samples were homogenized with deionized water at a ratio of 1:3.3 (w/v) muscle to water. The amount of water-extractable proteins was determined by the biuret method. Eight ml of clear extract from each treatment was reheated for 15 min at 70°C, removed, and cooled (0-2°C) immediately. Coagulum was removed by filtration (0.45 µm), and a biuret measurement made on the clear extract. These two values were used to calculate a water-extractable biuret-positive ratio (EBPR) value for a specific time/temperature treatment. The base value of 70°C was selected for the ratio because it represents a temperature slightly above that necessary for thermal inactivation of certain animal viruses required by USDA-APHIS/FSIS for certain imported canned meat products. Heat denaturation/coagulation of water-extractable, biuret-positive bovine and porcine compounds with subsequent solubility loss was a time/temperature-dependent process through 70°C. EBPR values for bovine and porcine muscles heated up to 60, 65, 67.5, 70, or 75°C with no holding time were 2.11, 1.23, 1.08, 1.07, 1.02 and 2.88, 1.65, 1.13, 1.04, and 1.02, respectively. Using 70°C as the critical denaturation/coagulation temperature, EBPR values for beef and pork were 1.07 ± .024 and 1.04 ± .066, respectively. Upper 95% confidence limits were 1.30 for beef and 1.12 for pork.
ABSTRACT
Ground pork longissimus was heated in glass tubes in a controlled temperature bath at 2 (control), 20, 40, 45, 50, 55, 60, 62.5, 65, 67.5, 70, 75, or 80°C for 15 min after the sample reached the desired temperature, removed and chilled (2°C) immediately. Treated samples were homogenized with deionized water at a ratio of 1:3.3 (w/v) muscle to water. The resulting water-extractable proteins were determined by the biuret method. Eight ml of clear extract from each treatment was reheated for 15 min at 70°C, removed, and chilled (2°C) immediately. Coagulated proteins were removed by filtration (0.45 µm). Soluble protein was used as an index of heat denaturation. Water-extractable biuret-positive protein losses were 5.7% from 2 to 45°C, 69.7% from 50 to 67.5°C and 4.3% from 70 to 80°C. Reheating each treatment extract to 70°C yielded 20.2% baseline biuret-positive soluble materials. The ratios of soluble proteins at each treatment temperature with the baseline critical value of 70°C were 5.1, 5.1, and 4.9 from 2 to 45°C; 4.5, 3.9, 2.7, 2.2, 1.5, and 1.2 from 50 to 67.5°C and 1.1, 1.0, and 1.0 from 70 to 80°C. This indicates that coagulation of water-extractable biuret-positive compounds is nearly constant at about 70°C. These results suggest that a ratio of water-extractable biuret-positive proteins from heat treated porcine muscle may be useful in determining the temperature to which pork has been heat processed.
