Effects of electric field strength and pulse rise time on physicochemical and sensory properties of apple juice by pulsed electric field

Effects of electric field strength (0-35 kV/cm) and pulse rise time (PRT) of 2 mu s and 0.2 mu s during pulsed electric fields (PEF) on enzymatic activity, vitamin C, total phenols, antioxidant capacities, color and theological characteristics of fresh apple juice were investigated. With increasing the electric field strength and PRT, the residual activity (RA) of polyphenoloxidase (PPO) and peroxidase (POD) decreased, almost complete inactivation of both enzymes was achieved at 35 kV/cm and 2 mu s-PRT. The content of vitamin C in apple juice decreased significantly (p<0.05) during PEF treatment, the largest loss was 36.6% at 30 kV/cm and 2 mu s-PRT. The content of total phenols was not affected by PEF with 2 mu s-PRT but decreased significantly (p< 0.05) by PEF with 0.2 mu s-PRT. The antioxidant capacity of apple juice was evaluated by DPPH radical scavenging activity, ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC). The DPPH value was not affected by PEF, whereas FRAP and ORAC values increased with increasing the electric field strength and decreasing the PRT. PEF-treated apple juice had a significantly higher (p<0.05) lightness (L) and yellowness (6) than the controlled sample. The apparent viscosity and consistency index (K) of apple juice decreased while the flow behavior index (n) increased with increasing the electric field strength, and apple juice treated at 2 mu s-PRT had significantly higher apparent viscosity than treated at 0.2 mu s-PRT. Industrial relevance: Apple juice is one of the most popular fruit juices, and it required strict treatment conditions to protect its quality, especially to prevent enzymatic discoloration. PEF is one promising novel non-thermal technique without compromising the flavor, taste and nutrition aspect of food. This study analyzed the effectiveness of PEF as a method of preserving qualities of apple juice, including inactivating enzymes which are crucial to quality control. Available data provided in this study will benefit the fruit juice industry. (C) 2012 Elsevier Ltd. All rights reserved.