Changes in lycopene content and quality of tomato juice during thermal processing by a nanofluid heating medium

The main aim of this study was to evaluate the effects of shortening common thermal processing through nanofluids on quality of tomato juice for the first time. For this purpose, three different temperatures (between 70 and 90 degrees C), nanoparticle concentrations (between 0 and 4%) and time (between 30 and 90 s) were selected for thermal processing of tomato juice in a shell and tube heat exchanger through central composite design. The findings indicated that while 4% nanoflluid at 30 degrees C for 30 s led to the best lycopene retention (96%) of tomato juice, hot water treatment (0% nanoparticle concentration) at 90 degrees C for 90 s resulted in the lowest lycopene retention (67%). The durations required for product to reach a certain temperature were dwindled and treated samples experienced lower color drops when higher nanoparticle concentrations were applied; a*/b* indices at 80 degrees C were 1.7, 1.8 and 1.9 for 0, 2 and 4% nanoparticles, respectively; indeed, higher nanoparticle concentration, and lower temperature and time led to higher lycopene retention and, as a consequence, higher a*/b* values. The effect of time on pH and acidity indices was not significant while temperature influenced those parameters significantly. Based on the indices considered, if temperature, concentration and time are set at 70 degrees C, 4% and 30 s, the best responses will be obtained. (C) 2018 Elsevier Ltd. All rights reserved.