Design of an ohmic reactor to study the kinetics of thermal reactions in liquid products

An ohmic reactor was developed at a laboratory-scale to study the kinetics of thermal reactions in liquid products such as milk and infant formula in the UHT domain. Temperature mapping revealed good thermal homogeneity with a maximum difference of 3 °C in the treatment cell. The ohmic reactor enabled determination of the electrical conductivity of the product under the real thermal conditions with a precision of ±15%. Reproducible thermal profiles were obtained with a 2.3% relative variation for the heating phase, 1% for holding and 20% for cooling. The FAST index, giving a global measurement of the extent of the Maillard reaction in dairy products, was used to estimate the reproducibility of a thermal reaction with an average standard deviation of 3.8%. Finally, a semi-empirical model was developed to predict product temperature history during a complete thermal treatment with good adjustment for heating and holding and acceptable adjustment for cooling.