Effect of ohmic heating treatment on rheological and textural properties of acid milk gels

Heat treatment is commonly applied in the manufacturing of yogurt to pasteurize milk and to change the milk composition properties to improve the quality. Ohmic heating is an alternative fast methods for food products in which heat is internally generated within food ingredients by the passage of an alternative electric current. The scope of this study is assessing the effects of ohmic heating thermal treatment on rheological and textural properties of acid milk gels formed by the hydrolysis of glucono-d-lactone. The response surface methodology (RSM) was used to find the optimal preheat treatment condition for acid milk gels manufacturing. Gels were formed from raw milk, which had been ohmically heated at different voltage gradient (20-210 V/cm) from 20°C to temperatures of 45-90 °C for different holding times (2-30 minu). The rheological properties of these gels were determined using dynamic low-amplitude oscillation in the Thermo Scientific Haake Mars II Rheometer. The large deformation properties were studied using a Texture Analyzer XT.Plus (Stable Micro Systems Ltd. UK). Effect of ohmic heating on pH and time of gelation onset, rate of gelation and structure strength of the final gel were determined, optimized and results were compared to those of conventional preheating at 90°C for 30 min.