Effects of high-intensity pulsed electric field processing conditions on lycopene, vitamin C and antioxidant capacity of watermelon juice

Watermelon juice was subjected to high-intensity pulsed electric fields (HIPEF). The effects of process parameters including electric field strength (30-35 kV/cm), pulse frequency (50-250 Hz), treatment time (50-2050 mu s), pulse width (1-7 mu s) and pulse polarity (monopolar/bipolar) on lycopene, vitamin C and antioxidant capacity were studied using a response surface methodology. Lycopene content was measured spectrophotometrically, vitamin C was determined by HPLC and antioxidant capacity through the inhibition of DPPH center dot (1,1-diphenyl-2-picrylhydrazyl) radical. Watermelon juice exhibited high retention of lycopene and antioxidant capacity when high electric field strengths, frequencies and pulse widths were applied. However, severe HIPEF treatments reduced vitamin C content. Maximal relative lycopene content (113%), vitamin C (72%) and antioxidant capacity retention (100%) were obtained when HIPEF treatments were set up at 35 kV/cm for 50 mu s using 7 mu s bipolar pulses at 200 Hz. (C) 2009 Elsevier Ltd. All rights reserved.