Comparisons of physicochemical properties of watermelon juice treated with pulsed electric fields and thermal pasteurization

Abstract

Pulsed electric field (PEF) treatment is a non-thermal and alternative pasteurization treatment for fruit juices. PEF applies short pulses of electricity to a liquid food sample which inactivates microorganisms and enzymes. Thermal pasteurization is commonly used to pasteurize juice in the fruit juice industry but the process tends to deteriorate color, nutrients, and overall juice appearance. The overall goal of this study was to determine the effects of PEF treatment (30 kv/cm for 57 ìs in bipolar 2 ìs pulses at 22°C) on color, lycopene content, vitamin C content, pH, °Brix, and microbial count when compared with the effects of thermal pasteurization (TP). Fresh watermelon juice was PEF-treated at the following flow rates (mL/min), 60, 80, 100, 120, 140, and 160, while the TP-treated juice was thermally pasteurized with the following conditions: 75°C at 15, 30, and 45 s; 80°C at 15, 30, and 45 s; 85°C at 15, 30, 45 s; 90°C at 15, 30, and 45 s. Vitamin C degradation was modeled and estimated for TP watermelon juice samples using Power Law and Arrhenius models. A fresh, untreated watermelon juice sample was used as the control for the TP treatments. Watermelon juice was passed through the PEF system without pulse application and used as a PEF-control. Triplicate experiments were conducted. For PEF treatments, lycopene content was significantly higher at the slowest flow rate of 60 mL/min. Vitamin C of watermelon juice was not significantly affected during PEF treatment regardless of the flow rate, while it significantly decreased (P < 0.05) with intensity of TP treatments. The reaction rate constant (K) of watermelon juice for TP treatment at 75°C was significantly less than juice sample treated at 80, 85, and 90oC, which indicated that the Power law model worked well at higher temperature TP treatments. This model was more appropriate for predicting vitamin C concentration of watermelon juice during thermal pasteurization. The calculated activated energy for the vitamin C degradation for TP vii treatments was 5.54 (kJ/mol), which was lower than the reported values for other juices. TP-treated juice had higher b*values than PEF-treated juice which indicated TP juice was more yellow in color. PEF treatments did not affect the pH of the juice compared to TP treatments which increased pH. PEF-control and PEF-treated samples had similar °Brix values. TP treatments significantly affected °Brix values of watermelon juice. These results indicate that PEF treatment is a better option for