Application of induced electric field for inner heating of kiwifruit juice and its analysis

Abstract

Kiwifruit juice is a popular liquid food with a large consumption. It usually needs high temperature sterilization before packaging and selling. Alternating magnetic field can produce alternating induced electric field, then a thermal effect is triggered. This study aims to explore the inner heating of kiwifruit juice via induced electric field and its impact on the physicochemical properties. Meanwhile, ultra-high temperature instantaneous sterilization (121°C, 5 s), and conventional heat treatment (93°C, 2 min) were conducted as controls, then effects were compared between these treatments. The results showed that the bacterial, mold and yeast colonies were completely eliminated, polyphenol oxidase activity decreased by 94.8%, and peroxidase activity decreased by 92.7%, at 1800 V and 6 mL/min. The induced electric field treatment and ultra-high temperature instantaneous sterilization had no significant effect on pH and titratable acid ( P ≥ 0.05). Conventional heat treatment increased soluble solid content by 5.3%. The induced electric field treatment resulted in the closest color and browning index to the fresh juice owing to moderate thermal effect. It also demonstrated minimal loss on total phenols and flavonoids contents after induced electric field treatment (7.1% and 2.7%, respectively). The heating effect caused by induced electric field has great application potential for the treatment of fruit juice. • Induced electric field was utilized for direct heating of kiwifruit juice. • Contact-less thermal effect and temperature rise on kiwifruit juice was evaluated. • The microbe and enzyme could be inactivated within 7.7 s via continuous-flow treatment. • The minimal loss of total phenols and flavonoid was achieved via induced electric field.