Pulsed electric fields process on juice quality improvement

Abstract

Pulsed Electric Field (PEF), which is a low-temperature treatment technology, has an ideal sterilization effect, and can maintain the quality of food to the greatest extent and reduce the cost of sterilization compared with thermal pasteurization. PEF is especially suitable for the sterilization of liquid foods such as fruit juice, milk, soup and liquid eggs. This study explored the effect of PEF on two different fruit juices, apple and navel orange juice, bacterial inactivation and characterized the physical and chemical properties of the juice treated by PEF and thermal pasteurization, compared with raw juice. Apple juice (Pink lady) and navel orange juice (Sunkist), extracted from a domestic extractor, was pasteurized by PEF treatment and heating treatment, compared them with raw juice respectively. The PEF process was undertaken by a designed high voltage pulsed electric filed unit, set with a PEF condition by a frequency of 2 Hz pulse, applied with 200 pulse per step and accumulation up to 800 pulses in total, an intensity of 42-47 kV/cm, and process duration time of 290 nano second. The thermal pasteurization was heated at 78C for 30 s by a laboratory water bath. The PEF condition, firstly, applied on Escherichia coli, Lactobacillus plantarum, and Leuconostoc mesenteorides. It is found the PEF process could have 3-4 log reduction from the initial colony forming units per milliliter (CFU/mL) of 7. Then, the effect on PEF on raw juice bacterial inactivation could reduce the microorganism less than 101 from the initial microbe CFU at 104-105, while conventional thermal pasteurization also had the same result. Juice physicochemical properties such as sugar content and antioxidant capacity were characterized. Generally, no significant change was observed in sugar content, however, the antioxidant capacity had a strange trend. Eventually, these measured variables were not significantly different between PEF process and thermal treatment pasteurization.