Time Temperature Heating Effect on Biuret-Positive Water-Extractable Porcine and Bovine Muscle Proteins

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.