Effect of Ohmic Heating on Bioactive Contents and Quality Characteristics of Apple Juice

Ohmic heating (OH) is an innovative method of converting electrical energy into heat. This study determined the effect of temperature and time on total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (AA) in clear apple juice that was heat‐treated using conventional heating in a water bath and OH at the voltage gradients of 10 and 20 V/cm. Additionally, the degradation kinetics for the reduction rates of these properties over time were assessed. The TPC, TFC and AA values of fresh apple juices prepared from concentrate were 19.38 ± 0.53 mg GAE/100 mL, 2.96 ± 0.10 mg CE/100 mL and 12.05 ± 0.17 μmol TE/100 mL, respectively. OH at 10 V/cm for 30 min at 80°C reduced the TPC, TFC and AA values of apple juice to 16.75 ± 0.90, 2.48 ± 0.36 and 4.66 ± 0.17, respectively, while these values decreased to 15.14 ± 1.18, 2.55 ± 0.07 and 4.67 ± 0.07 for OH at 20 V/cm, respectively. In conventional heating, the TPC, TFC and AA values of juices were 16.94 ± 0.19 mg GAE/100 mL, 1.98 ± 0.03 mg CE/100 mL and 10.80 ± 0.97 μmol TE/100 mL, respectively. Therefore, OH treatments were more effective in protecting TFC, and a greater decrease in AA values was observed. Ohmic heating caused a 9.4% increase in the hydroxymethyl furaldehyde (HMF) content while this increase was 57.1% in conventional heating. OH, especially at 20 V/cm, preserved the original color of clear apple juice better than conventional heating, as indicated by the lower values of total color changes. OH was found superior for the heat treatment of apple juices, minimizing browning, HMF formation, and quality loss, while following first‐order degradation kinetics for the reduction rates in the TPC, TFC, and AA values.