Calorimetric study of changes induced by preservatives in liquid egg products

In our tests we aimed to study the effects of additives normally used in liquid egg products on the calorimetric properties of liquid egg samples. Raw liquid egg white (pH=8.9±0.1), liquid egg yolk (pH=6.5±0.2) and whole liquid egg (pH=7.1±0.2) broken up in industrial conditions were used in our measurements. Sodium benzoate and potassium sorbate were added to the samples to achieve solutions of 0.1, 0.3 and 0.5 g/L concentrations. We used citric acid to prepare liquid egg products with various pH value (5.5, 5.0 and 4.5). The calorimetric tests were performed with MicroDSC III device. Liquid egg samples were heated up from 20°C to 95°C generally with a heating rate of 1.5°C/min. Sample weights were 500 mg±0.1 mg and water was used as reference solution. Evaluation was performed by Seftsoft2000 software, a component of the device. Our measurements have shown significant changes in calorimetric parameters of liquid egg samples by decreasing the pH value to 5.0. In addition to the reduced enthalpy due to acidification of samples, a decrease in denaturation temperature was also observed in the egg white. While the native egg white started to precipitate at 60°C, at pH 5.0 the denaturation was already started at 54.5°C. When sodium benzoate and potassium sorbate were added to liquid egg products a significant change of the tested calorimetric values was only found in the liquid egg samples containing the preservative at the concentration of 0.5 g/L.