Evaluation of the Effect of Different Heat Pretreatment on Chemical Properties of Grape Juice
Subject Areas : Microbiology
1 - Assistant Professor of the Department of Food Science and Technology, Tabriz Branch, Islamic Azad University, Tabriz, Iran.
2 - Ph. D. Student of the Institute of Food Science and Technology, Mashhad, Iran.
Keywords: Grape Juice, Microwave Heating, Ohmic Heating, Thermal Heating,
Abstract :
Introduction: Grape is one of the most cultivated fruit in the world. Recently various methods have been employed to improve the efficiency of juice extraction. In this research project Gizil Ozom variety (red grape) in the form of paste is used as raw material to extract the juice. Materials and Methods: Grape mash is subjected to ohmic heating, microwave heating and conventional thermal treatment before pressing. The juice samples were pasteurized at 88°C for 2 minutes. After production of the juice the effects of ohmic, microwave and conventional heating on the yield of grape juice, anthocyanin content, total phenolics, viscosity, pH, brix and total acidity were determined before and after pasteurization. Results: The results showed that the highest yields were obtained when microwave and ohmic treatments were applied to the samples and the yields were 8% and 13.2% for ohmic and microwave heated samples, respectively. Application of ohmic and microwave operations prior to pressing step, caused increases in anthocyanin and phenolic contents of grape juice in contrast to the control samples (P<0.05). Brix was the highest for the sample treated with microwave. Significant differences were observed in pH values for the samples treated with ohmic heating. Conclusion: The results of this study showed that microwave and ohmic heating can be used as pretreatments for the production of grape juice.
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