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Effect of pulsed electric field treatment on polyphenol oxidase, total phenolic compounds, and microbial growth of apple juice

A pulsed electric field (PEF) process was applied to unclarified apple juices at 30 and 40 kV cm–1 for 50, 100, 150, and 200 pulses after preheating to 40 °C. Afterwards, polyphenol oxidase (PPO) enzyme levels, loss of total phenolic (TP) compounds, and alterations of the physiochemical parameters of the apple juice were determined. | Turkish Journal of Agriculture and Forestry Turk J Agric For (2013) 37: 772-780 © TÜBİTAK doi:10.3906/tar-1211-17 http://journals.tubitak.gov.tr/agriculture/ Research Article Effect of pulsed electric field treatment on polyphenol oxidase, total phenolic compounds, and microbial growth of apple juice 1 2, 3 Mustafa Fatih ERTUGAY , Mehmet BAŞLAR *, Fatih ORTAKCI Food Engineering Department, Agricultural Faculty, Atatürk University, Erzurum, Turkey 2 Food Engineering Department, Chemical and Metallurgical Engineering Faculty, Yıldız Technical University, İstanbul, Turkey 3 Department of Nutrition, Dietetics, and Food Science, Utah State University, Logan, UT, USA 1 Received: 06.11.2012 Accepted: 06.04.2013 Published Online: 23.09.2013 Printed: 23.10.2013 Abstract: A pulsed electric field (PEF) process was applied to unclarified apple juices at 30 and 40 kV cm–1 for 50, 100, 150, and 200 pulses after preheating to 40 °C. Afterwards, polyphenol oxidase (PPO) enzyme levels, loss of total phenolic (TP) compounds, and alterations of the physiochemical parameters of the apple juice were determined. Total yeast/mold and mesophilic bacteria loads were periodically evaluated during storage at 25 °C for a 3-month period and the cloud quality of the apple juice was analyzed after storage. The results of the present study have indicated that total yeast/mold and mesophilic bacterial activity could be completely inactivated under all PEF processing conditions. Moreover, no microbial activity occurred in PEF-treated apple juices during the 3-month storage period, whereas the control had more than a 6 log cfu mL–1 microbial load at the end of storage. PPO activity became completely inactive at 100 or more pulses at 40 kV cm–1, while residual activity decreased by up to 32.1%, 7.0%, 2.9%, and 1.6% at 30 kV cm–1 at 50, 100, 150, and 200 pulses, respectively. Kinetic data for PPO activity and TP content were described using a first-order kinetics model with a high R2 .