In this research, our main idea was to apply thermal processing by nanofluids instead of conventional pasteurization processes, to shorten duration of thermal procedure and improve nutritional contents of fruit juices. Three different variables of temperature (70, 80 and 90 °C), nanofluid concentration (0, 2 and 4%) and time (30, 60 and 90 s) were selected for thermal processing of tomato juices by a shell and tube heat exchanger. The results demonstrated that 4% nanofluid concentration, at 30 °C for 30 s could result in 66% vitamin C retention of fresh juice while it was about 56% for the minimum nanofluid concentration and maximum temperature and time. Higher nanoparticle concentrations made tomato juices that require lowered thermal durations, because of better heat transfer to the product, and total phenolic compounds dwindle less severely; In fact, after 30 s thermal processing at 70 °C with 0 and 4% nanoparticles, total phenolic compounds were maintained by 71.9 and 73.6%, respectively. The range of total soluble solids for processed tomato juices was 5.4-5.6, meaning that nanofluid thermal processing could preserve the natural condition of tomato juices successfully. Based on the indices considered, a nanofluid thermal processing with 4% nanoparticle concentration at the temperature of 70 °C for 30 s will result in the best nutritional contents of final tomato juices.
Keywords: Heat exchanger; Nano-fluids; Tomato juice; Total phenolics; Vitamin C.