W. E. Townsend

Rapid fluorometric analysis of acid phosphatase activity in cooked poultry meat

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.

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.

Effect of Heating on Water Soluble Biuret-Positive Compounds of Canned Cured Pork Picnic Shoulder

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.

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.

Effect of air movement during fermentation on certain properties of natural flora and starter culture-fermented sausage

Effects of air movement (0, 5, 20 and 35 changes/min) during fermentation on certain chemical, physical and microbiological properties of a fermented and cooked summer sausage were determined. Four batches of summer sausage were prepared. Half of each batch was fermented by natural flora and the other half by a Pediococcus cerevisiae starter culture. Sausages were fermented in chambers at 38°C with 94% RH, and samples were taken at 0, 6, 12, 18 and 24 h during fermentation. Samples were also taken after heat processing and overnight chilling. Air movement during fermentation had no significant effect on pH, lactic acid content, cured color development or proximate composition regardless of method of fermentation. Removal of sausage casing was very difficult for all natural flora sausage chubs that were fermented at 5, 20 and 35 air changes/min; however, ease of casing removal improved somewhat at 18 and 24 h of fermentation for sausages made with natural flora and fermented at 0 air change/min. Regardless of air movement treatment, removal of casing from sausages made with starter culture was poor at 6 h of fermentation, but was much improved at 12 h of fermentation and thereafter. Microbial growth was fastest and highest among the natural flora sausage fermented without air flow. An undesirable surface film which developed on the natural flora sausage fermented without air flow consisted of gram negative rods and gram positive cocci.

Evaluation of a Sound Velocity Analyzer for Estimating Maximum Internal Temperature to Which Meat Products Have Been Heat Processed

The sound velocity (SV) values of a variety of solutions (distilled water, saline, silicon dioxide, bovine serum albumin, coagulated beef protein) were determined as the temperature of the solution was increased from 10 or 20° to 71°C. Few differences were found in the SV values for the various types of distilled water; however, there was an increase in SV values as the concentration of saline increased. Level of silicon dioxide or bovine serum albumin had no significant effect on SV values; however, there was an increase in SV values as percentage of precoagulated beef protein solids in solution increased. The sound velocity analyzer used in this study was found not to be sensitive enough to detect the onset of coagulation of saline soluble proteins and, therefore, would not lend itself as an objective method which could be related to end-point temperature of meat products.