The Application Of Pulsed Electric Fields On Pear Juice Processing

The traditional thermal pasteurization processes are effective on sterilization of pear juice. However, they bring about many adverse effects. For example, they may darken the color of the juice, cause the undesirable cooking flavor, and destroy sensitive components, etc. To evaluate the application of non-thermal processing technology on the processing of high-quality pear juice, inactivation of microbe and enzyme, and effect on the quality of pear juice by PEF were investigated.The processes for protecting colour and maintaining the stability of cloudy pear juice were investigated. The results showed that browing of pear juice was inhibited significantly by adding 3.0 g·L-1 citric acid and 1.0 g·L-1 ascorbic acid before pear crashing. It was important to maintian the stability when producing cloudy pear juice. Complex stabilizers, including pectin 3.0 g·L-1 and CMC-Na 3.0 g·L-1 were added to the juice and the product was twice homogenized under 20 MPa.Effects of PEF intensity and treatment time and temperature on inactivation of microbe were investigated. The inactivation of microbe in the inoculated pear juice increased with the increase of applied electric field intensity and treatment time. The higher the temperature of the sample, the more effective the PEF inactivation of microbe. The sensitivity of different microbe to PEF were as follows: E.coli >Salmonella >L.innocua >S. cerevisiae. Cell death of microbe by PEF was probablely caused by the combination of cell membrane rupture, cytoplasm clumping and loss of cytoplasm.Little inactivation could be achieved for polyphenol oxidase (PPO) under low intensity of PEF treatment. However, when 35 kV/cm and 1200μs were applied to PPO in a buffer solution, an 91.7% PPO inactivation was achieved. The inactivation of PPO by PEF was also promoted with the increase of temperature. The first-order inactivation model which could be described as 0.0000220.12920RA RA ee Et=×?×××was valid for describing the inactivation of pear PPO by PEF. The RA measured experimentally and the RA projected by first-order inactivation model had a closer correlation, the regressive coefficient was 0.9536. The second-order polynomial equation was a suitable model to analyze the inactivation of PPO using PEF technology since it can supply PEF fators, including PEF intensity, treatment time and temperature. The model was described as RA=86.46+3.5513E-0.01471t+0.1118T+ 0.000025t2 -0.1087E2-0.006125T2-0.001803Et-0.000389tT-0.003457TE. Based on the results, electric field strength has the largest influence on PEF inactivation of PPO.PEF processing didn't cause significant changes in physico-chemical properties,nutrition and volatile aroma compounds. It was concluded that PEF treatment could maintain the flavor and quality of pear juice. The results of storage experiment showed that synergistic effect of PEF and low temperature storage made a significant decrease on PEF treated cells, and brought the pear juice a shelf life more than 2 months in 4℃.