Ohmic blanching effects on drying of vegetable byproduct

Ohmic blanching could be used as an alternative fast blanching method in vegetable processing. Artichoke is a vegetable that is a good source of natural antioxidants. In this study, artichoke byproduct was pretreated with ohmic blanching (25 and 40 V/cm at 85C) and water blanching (at 85 and 100C). The ohmic blanching (40 V/cm) at 85C was able to show similar peroxidase inactivation times (310 ± 2 s) with the water blanching at 100C (300 ± 2 s). The retention of vitamin C and the total phenolic content was found to be highest in the byproduct blanched ohmically by 40 V/cm voltage gradient at 85C. Blanched artichoke byproducts were then dried in the fluid-bed drier. The drying process was optimized by using response surface methodology. Optimum drying parameters were obtained as 80C, 0.8 m/s and the pretreatment of ohmic blanching at 40 V/cm voltage gradient. © 2009 Wiley Periodicals, Inc

JOURNAL OF FOOD ENGINEERING

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

JOURNAL OF FOOD ENGINEERING

Ohmic heating is an alternative fast heating method for food products. In this study, the pea puree samples were blanched ohmically and conventionally. The ohmic blanching was performed by application of four different voltage gradients in the range of 20-50 V/cm. The puree samples were heated from 30 degrees C to 100 degrees C and held at 100 degrees C to achieve adequate blanching. The conventional blanching was performed at 100 degrees C water bath. The ohmic blanching applied by using 30 V/cm and above voltage gradient inactivated peroxidase enzyme at less time than the water blanching. The ohmic blanching at 50 V/cm gave the shortest critical inactivation time of 54 s with the best colour quality. First order reaction kinetics adequately described the changes in colour values during ohmic blanching. Hue angle is the most appropriate combination (R-2 = 0.954), which describes closely the reaction kinetics of total colour changes of pea puree for ohmic blanching at 20 V/cm. (c) 2005 Elsevier Ltd. All rights reserved

Dielectrical properties of food materials - 1: Factors affecting and industrial uses

WOS: 000225321400006PubMed ID: 15615429The electrical properties of foods and biological products have been the most valuable factors in the novel food technology. They have been defined both from electromagnetic field concepts and from the electrical-circuit point of view Recently, these properties are used to assess the characterization of the processes based on electrical methods: electromagnetic, electro-processes. This article is a review of dielectrical properties of food materials. It also includes factors affecting the dielectrical properties of foods and their industrial uses

Effect of voltage gradient on ohmic thawing characteristics of sour cherry juice concentrates for the temperature range of -18? to +4?

###EgeUn###Frozen sour cherry juice concentrates having 15%, 30%, 40% and 50% total soluble solid (TSS) contents were thawed by ohmic thawing (OT; 10 V/cm, 15 V/cm and 20 V/cm) and conventional thawing (CT; at 4 ?). To enhance the electrode-sample contact during OT, the thawing cell was custom-designed. Thawing times were shortened about 90% by OT. Thermal images were taken to determine temperature homogeneity. As OT proceeded, a small amount of frozen sample having a relatively lower density raised up to the surface of the sample. It resulted in temperature heterogeneity in the surface due to relatively rapid temperature increment in thawed regions during OT. The change of effective electrical conductivity (EEC) in the temperature range of -18 ? and 4 ? was determined and it varied between 0.005 and 0.25 s/m. For the same temperature, EEC increased as TSS increased up to 40% (p<0.05). EEC–temperature relations were characterized by a polynomial model. © The Author(s) 2019

Dielectrical properties of food materials - 2: Measurement techniques

WOS: 000225321400007PubMed ID: 15615430The knowledge of the electrical properties of the materials to be processed or measured is important in the design of the equipment. Dielectric properties determine the behavior of the materials, when subjected to high frequency or microwave fields in dielectric heating processes or cooking. This article is a review of the measurement techniques of the dielectrical properties of food materials. This study also includes the classification of electrical properties and their importance in food processing

Rheological characteristics of quince nectar during ohmic heating

Electrical heating of food products provides rapid and uniform heating, resulting in less thermal damage to the product. In this study, ohmic heating as an electrical heating method was applied to the quince nectar by matching the same heating curve of conventional method by changing voltage gradient (10-40 V/cm) at 50 Hz. The change of rheological constants of quince nectar was determined for different holding times (0, 10, 15, 20, and 30 minutes) in the temperature range of 65-75°C by using concentric type viscosimeter. Shear stress-shear rate data were fitted to the Newtonian, Bingham, Herschel Bulkley, Power law and Casson Models. It was found that Herschel-Bulkley model was the best model to fit the experimental rheogram adequately since higher regression coefficients (R2; 0.9997) and low standard errors (SE; 0.054) were obtained by Herschel-Bulkley equation compared to other model equations. It was concluded that quince nectar showed time independent non-Newtonian pseudoplastic character during heating in the range of 20-75°C, independent on heating method. The activation energy values were 9.88±3.24 kJ/mol and 10.08±2.53 kJ/mol for ohmic heating and conventional heating respectively. Results showed that there was no electrical effect rather than thermal effects of ohmic heating since similar rheological constants were obtained with both methods statistically (p < 0.05). Ohmic heating could be recommended as an alternative fas heating method for fruit nectars

The effects of concentration on electrical conductivity of orange juice concentrates during ohmic heating

Ohmic heating is an alternative heating technique, using an electrical current passing through the food product. It can be specially used in pumpable food lines as an alternative heating unit. In this study, orange juice concentrates having 0.20-0.60 mass fraction soluble solids were ohmically heated by using five different voltage gradients (20-60 V/cm). The dependence of electrical conductivity on temperature, voltage gradient and concentration were measured. The ohmic heating system performance coefficients were calculated by using the energies given to the system and taken by the orange juice samples. The mathematical model results, taking system performance coefficients into account, were compared with experimental ones. The predictions of the mathematical model were found to be very accurate. © 2004 Springer-Verlag.2001/BIL/002 2001/MUH/03Acknowledgement This study was partially supported by Ege University Science-Technology Research and Application Center (EBILTEM) Project No: 2001/BIL/002, Ege University Scientific Projects Fund Project No: 2001/MUH/03, ETAP Agricultural and Food Products Packaging SA Turkey and Pinar Dairy Products SA Turkey. -