High-intensity pulsed electric fields or thermal treatment of broccoli juice: the effects of processing on minerals and free amino acids

This research evaluated the influence of high-intensity pulsed electric fields (HIPEF) parameters, electric field strength (15-35 kV/cm), treatment time (500-2000 mu s) and polarity (monopolar or bipolar mode) on minerals and free amino acids content of broccoli juice. Additionally, HIPEF-processed broccoli juice was compared with thermally treated (90 degrees C/60 s) and untreated juices. In general, HIPEF parameters significantly influenced the content of minerals and free amino acids, except Cu, S, P, Trp, Ala, His, and Tyr, which were not influenced by electric field strength, treatment time and/or polarity. At the strongest HIPEF conditions (35 kV/cm for 2000 mu s) in bipolar mode, an increment or not significant changes in the mineral content in comparison to fresh broccoli juice was observed. Iron (214.2%), manganesus (117.7%) and zinc (148.4%) were the minerals with the greatest relative augment. While, the highest amino acid retention was histidine (159.3%), and lysine (157.8%). Increment in mineral content was associated to electrode corrosion; while the increase in amino acid content was related to the increment in the activity of enzymes associated with their biosynthesis. Changes in the content of free amino acids depended on HIPEF treatment conditions applied and the amino acid evaluated. Significant losses of minerals and free amino acids were reached after thermal processing of broccoli juice. Overall, HIPEF-treated broccoli juice had superior mineral and free amino acids content than those thermally treated.