Influence of mild electric field (MEF) on polyphenol oxidase and quality attributes of pineapple juice during ohmic heating

Abstract

Fresh pineapple juice was ohmically heated up to 80 ± 2 °C (held for 1 min), followed by cooling. The voltage gradient (VG) of 16 V/cm was kept constant for the come-up period to maintain an identical thermal history. The effect of VG on Polyphenoloxidase (PPO), color, hydroxymethylfurfural (HMF), and total phenolic content (TPC) was evaluated by maintaining 16–36 V/cm at the temperature (80 ± 2 °C). The PPO activity was reduced to 50.06 and 56.67% by hot water (HWT) and ohmic heating (OH) (16 V/cm) treatment, respectively. PPO inactivation showed exponential (k = −0.342; R2 = 0.965) relationship with the VG (16–36 V/cm). The a* value (redness) increased with the VG, whereas the b* (blue-yellow) and hue value remained unchanged up to 16-32V/cm. Both OH and HWT treatments caused an increase in HMF content from 0.145 to 0.351 and 0.233 mg/100 mL, respectively. The TPC content reduced by 18% in HWT, while only 7–10% losses were observed in OH within 16–24 V/cm. The development of HMF with VG was best expressed by the polynomial model (R2 = 0.976–0.994), whereas the TPC degradation followed quadratic relation (R2 = 0.856 ± 0.906). Therefore, it was observed that VG plays an important role in OH-based enzyme inactivation method for pineapple juice.