Browsing by Author "Içier, F"

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    Moderate Electric Treatment Applications on Pomegranate Juice Production: Yield and Physicochemical Properties
    Demirdöven, A; Yildiz, H; Içier, F; Baysal, T
    Moderate electric treatment (MET) is based on the growth of pores in cell membranes as a result of electric field applications. In this study, effects of MET applications on yield and quality of pomegranate juice production were investigated. MET was applied to whole pomegranate fruits between 10 and 60 V/cm voltage gradients for 15 s in a pilot scale continues drum-type MET system. Pomegranate juice yields were increased by 2.11-6.99% with electrical treatment. The highest total phenolics were determined at 60 V/cm applications and the highest anthocyanin, antioxidant capacity, ascorbic acid, a value and total color differences were determined at 10 V/cm applications. The electrical treatment significantly decreased the viscosity of juice. It was concluded that MET application could be applied as a pretreatment in pomegranate juice production. Practical ApplicationsJuice extraction is a slow and highly energy-consuming step in the production of fruit juices; thus, various methods have been tried to improve efficiency. And there is an additional effect on juice yield caused by the electric current. Moderate electric treatment (MET) is effective in destroying cellular membranes and different types of electroporation units could be used for the structure of fruits or vegetables and also according to the production method. Through this study, a high potential of MET for the yield and functional improvement of pomegranate juices was found. The drum-type MET system which was used in the study can be used for whole materials without significant temperature increases. In addition, MET treatments can be used to increase the press yield as a nonthermal application and it will eliminate heat exposures, and also drum-type MET system can be adapted to the industrial production lines.
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    Polyphenoloxidase deactivation kinetics during ohmic heating of grape juice
    Içier, F; Yildiz, H; Baysal, T
    The heating method affects the temperature distribution inside a food, and directly modifies the time-temperature relationship for enzyme deactivation. Fresh grape juice was ohmically heated at different voltage gradients (20, 30, and 40 V/cm) from 20 degrees C to temperatures of 60, 70, 80 or 90 degrees C and the change in the activity of polyphenoloxidase enzyme (PPO) was measured. The critical deactivation temperatures were found to be 60 degrees C or lower for 40 V/cm, and 70 degrees C for 20 and 30 V/cm. Various kinetic models for the deactivation of PPO by ohmic heating at 30 V/cm were fitted to the experimental data. The simplest kinetic model involving one step first-order deactivation was better than more complex models. The activation energy of the PPO deactivation for the temperature range of 70-90 degrees C was found to be 83.5 kJ/mol. (c) 2007 Elsevier Ltd. All rights reserved.