Effect of Induced Electric Field on Physical and Chemical Characteristics of Continuous-Flow Blueberry Puree

The non-contact induced electric field (IEF) was applied in the treatment of continuous-flow blueberry puree. Changes in impedance and polyphenol oxidase (PPO) activity of the sample with different treatment time (9, 18, 27, 30, 36, 45 min) at different excitation voltages (100, 150, 250 V) and temperature (65, 75, 85℃) were investigated. Meanwhile, the color, particle size distribution, rheological properties, flavor and volatile components of different (fresh, conventional-heating-treated, IEF-treated) blueberry puree products were analyzed and compared. It was found that the impedance of blueberry puree gradually decreased with the increasing of treatment time and temperature. The inactivation of PPO was enhanced by IEF. After 30 min of IEF treatment at 250 V and 85℃, PPO was completely inactivated. The L^* and a^* of the IEF-treated blueberry puree were 30.37 and 6.42 respectively, which were significantly greater than those of the fresh and conventional-heating-treated ones (P<0.05). Particle size distribution, viscosity and flavor of IEF-treated blueberry puree were much closer to those of the fresh sample, in comparison with the conventional-heating-treated one. Results indicated that the relative weak induced of electric field/current was potential to stabilize the color and flavor components in blueberry puree, which was beneficial to slow the color loss and flavor change caused by heat treatment. This investigation aims to provide a certain thermotical reference for the high-quality processing of fruit puree by using weak induced electric field.