Protótipo de aquecedor ôhmico para pasteurização de leite

Abstract

Ohmic heating has emerged as a promising alternative for processing liquid foods, enabling fast, relatively uniform heating and the potential to reduce nutritional losses and energy consumption. However, information is still scarce regarding suitable electrical conditions for milk treatment and the performance of laboratory-scale equipment. This study aimed to design and build a prototype of a parallel-plate ohmic heater for milk pasteurization, as well as to compare different ways of applying electric current and to evaluate the influence of electric fields and frequencies on fluid heating. Preliminary batch tests using direct and alternating current in a simplified setup were first carried out to verify process feasibility. Subsequently, a prototype made of acrylic and 304 stainless steel, thermally insulated and powered by an alternating current source coupled to a power amplifier module, was developed and operated with electric fields of 5, 8, and 10 volts per centimeter at frequencies of 30, 45, and 60 hertz. Milk temperature, voltage, current, and electrical conductivity were monitored, and experimental heating times were compared with values estimated using a mathematical model. Tests with direct current showed intense foam formation and deposits on the plates, indicating undesirable reactions and limiting its use. With alternating current, the prototype heated milk to the rapid pasteurization condition, revealing a strong effect of electric field intensity on processing time and a smaller influence of frequency within the range evaluated. Experimental times remained within the calculated limits, confirming the suitability of the proposed design and the feasibility of ohmic heating of milk at the laboratory scale. However, the use of more precise instrumentation and complementary microbiological studies is recommended.