Temperature dependent electrical conductivities of fruit purees during ohmic heating

Ohmic heating takes its name from Ohm's law; the food material switched between electrodes has a role of resistance in the circuit. In this study, the apricot and peach purees were heated on a laboratory scale static ohmic heater by applying voltage gradients in the range of 20-70 V/cm. The voltage gradient was statistically significant on the ohmic heating rates for both purees (P < 0.05). The linear temperature dependent electrical conductivity relations were obtained. Bubbling was observed above 60°C especially at high voltage gradients. The ohmic heating system performance coefficients were in the range of 0.49-1.00. The unsteady-state heat conduction equation for negligible internal resistance was solved with an ohmic heating generation term by the finite difference technique. The predictions of the mathematical model using obtained electrical conductivity equations were found to be very accurate. © 2005 Elsevier Ltd. All rights reserved

Influence of ohmic heating on rheological and electrical properties of reconstituted whey solutions

WOS: 000273189800010Reconstituted whey solutions (in the range of 8-24% w/v solute concentrations) were heated from 20 degrees C to prescribed temperatures (30, 40,50, 60, 70 or 80 degrees C) ohmically by applying voltage gradients of 20, 30 or 40 V/cm, and conventionally at water bath. Electrical conductivity changes with increasing temperature were linear during ohmic heating. Whey solutions have non-Newtonian characteristics since Herschel-Bulkley model satisfactorily fitted the experimental shear stress-shear rate data. "n" values were in the range of 0.520-1.503. The whey solution having 24% concentration had a yield stress of 0.006-0.024 Pa at low temperatures. Although temperature and concentration were critical factors for the consistency and the electrical conductivity changes during heating (p < 0.01), the voltage gradient was not effective statistically. The high correlation (between -0.910 and -0.991) was obtained between changes of electrical conductivity and consistency coefficient values during ohmic heating. Since activation energies for ohmic heating (26.34-45.79 kJ/mol) depending on solute concentration were lower than conventional heating (26.70-50.04 kJ/mol), reconstituted whey solutions were less sensible to temperature changes during ohmic heating. It was recommended that ohmic heating could be applied as a faster alternative heating method in the whey processing. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.Agriculture, Forestry and Veterinary Research Grant Committee (TOVAG) of Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [1060221]; Ege University Science FoundationEge University [03/BIL/024]This study was the part of the projects financially supported by Agriculture, Forestry and Veterinary Research Grant Committee (TOVAG) of Scientific and Technical Research Council of Turkey (TUBITAK, Project No. 1060221), and Ege University Science Foundation (Project No. 03/BIL/024). Author wishes to thank PINAR Dairy Industry (Turkey) for providing whey powder for this stud

Rheological behavior of sour cherry juices concentrated by ohmic and conventional evaporation processes under vacuum

ICIER, Filiz/0000-0002-9555-3390WOS: 000558531400001In this study, sour cherry juice was evaporated up to 65% total soluble solid content (TSSC) under vacuum (25 kPa) by ohmic-assisted vacuum evaporation (OAVE) and vacuum evaporation (VE). the effects of voltage gradients (10-14 V/cm) on the rheological behavior of sour cherry concentrates having different TSCC (30%-65%) were determined, and compared with those of VE. in general, the shear stress increased as the shear rate increased for all concentrations. Since the statistical error values of Power Law and Newton models were similar (p > .05), the most appropriate model describing the rheological behavior was chosen as Newton model being more nominative and mathematically simpler. the viscosity of concentrates (30%-65%) varied in the range of 0.003-0.119 Pa.s. the increase in the viscosity values depending on TSSC during evaporation was similar for both processes. Thus, OAVE could be beneficial alternative method to VE for the purpose of producing fruit juice concentrates having similar rheological properties. Practical applications It is an alternative evaporation method in the literature in recent years by integrating ohmic heating into the evaporation process. However, in order for the ohmic evaporation process to be an alternative, it is necessary to provide qualities of fruit juices similar to or better than the vacuum evaporation process. One of the most important features for the transportation of fruit juices in industrial transport lines is rheological properties. in this study, it is important to determine that the consistency of the product resulting from the use of ohmic heating support in evaporation does not differ from the conventional method. the data obtained in this publication will constitute an important data infrastructure for scaling OAVE operation to industrial systems as an alternative.Turkiye Bilimsel ve Teknolojik Arastirma KurumuTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [114O117]; Ege Universitesi [2015/BIL/010]Turkiye Bilimsel ve Teknolojik Arastirma Kurumu, Grant/Award Number: 114O117; Ege Universitesi, Grant/Award Number: 2015/BIL/01

Drying of tomato pomace in daylight simulated photovoltaic-assisted drying system: Effects of daylight intensity and application mode

It was aimed to dry a by-product of tomato paste production (tomato pomace) by minimizing the losses valuable components and reducing energy consumption. In this concept, a daylight simulated photovoltaic-assisted dryer (DPVD) applying the daylight in different modes and intensities during drying was custom-designed. The effects of daylight applications on the change of some quality characteristics of tomato pomace and system performance characteristics were investigated, and the optimum drying condition was determined. The process conditions included the combination of three different daylight application modes (UV-blocked daylight via solar tube-DLST, DLST + LED, and LED) and three different daylight intensities (2,500, 7,500, and 10,000 lux). The drying was applied for 240 min at constant air temperature (60 degrees C) with an air velocity of 2 m/s. The moisture content and the water activity values of dried tomato pomace were 8.86 +/- 2.00% and 0.57 +/- 0.10%, respectively. The lycopene and beta-carotene losses after drying were determined as 68.36 +/- 4.32% and 65.66 +/- 4.33%, respectively. The energy and exergy efficiencies of the system were in the range of 19.56%-35.73% and 5.10%-17.05%, respectively. The optimum condition meeting the criteria of superior quality and high-performance characteristics was obtained by applying DLST at 7,500 lux (desirability 0.728). In the performance improvement studies, it has been concluded that all the energy required for the process could have been fulfilled as 100% from solar energy with the support of photovoltaic panels. In other words, it was demonstrated that the developed DPVD system could be used to dry the tomato pomace not only in terms of providing high food quality and safety, but also in terms of having high energy efficiency.The authors thank TUBTAK TOVAG and Ege universitesi BAP for financial supports to this study. This study was a part of the PhD thesis Sunlight Simulated and Photovoltaic Assisted Drying System Configuration, Performance Assessment and Investigation of Using for Drying of Tomato Pulp. The drying system was designed and set up in Project TUBITAK 119O132. The experimental design was applied within the scope of the Ege universitesi BAP project FDK-2019-20627. Author (Damla Bayana) thank to TUBTAK fellowship support of BIDEB 2211C program and YOK 100/2000 Renewable Energy Sources and Technologies fellowship program.TUBTAK TOVAG; Ege universitesi BAP; TUBTAK; TUBITAK [119O132]; Ege universitesi BAP project [FDK-2019-20627

OHMIC THAWING OF FROZEN BEEF CUTS

WOS: 000299413300002In this study, the application of ohmic heating to thaw the frozen beef cut samples was investigated. The center temperature of different sample sizes of beef cuts (2.5 cm x 2.5 cm x 5 cm; 2.5 cm x 5 cm x 5 cm; 3: 5 cm x 5 cm x 5 cm) was aimed to reach +10C from -18C. The ohmic thawing was performed by the application of different voltage gradients (10, 20 and 30 V/cm), whereas the conventional thawing was performed at controlled conditions (25C, 95% RH). The effects of sample size, thawing method and voltage gradient on thawing time, drip loss, color, temperature homogeneity and EUR were investigated. Significant differences were found between thawing methods in terms of the temperature homogeneity, the thawing time and the thawing loss (P < 0.05). The results indicated that as the voltage gradient increased, the thawing time decreased, while the thawing loss remained unchanged. There was a decrease in the EUR (4770%) with the increase in the sample size and the voltage gradient applied during ohmic thawing. The results of this study will provide valuable data for the design of the industrial ohmic thawing systems and give useful insights to further studies on this subject.Agriculture, Forestry and Veterinary Research Grant Committee (TOVAG) of Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [107O898]This study was the part of the project financially supported by Agriculture, Forestry and Veterinary Research Grant Committee (TOVAG) of Scientific and Technical Research Council of Turkey (TUBITAK, Project no. 107O898)

RHEOLOGICAL CHARACTERISTICS OF QUINCE NECTAR DURING OHMIC HEATING

WOS: 000269932000012Electrical 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 degrees 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 (R-2; 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 degrees C, independent on heating method. The activation energy values were 9.88 +/-.24 kJ/mol and 10.08 +/-.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 fast heating method for fruit nectars

Ohmic Heating of Liquid Whole Egg: Rheological Behaviour and Fluid Dynamics

WOS: 000293791000017Although ohmic heating is used as an alternative heating method for liquid egg products commercially, there is a lack of information on the change of rheological properties and fluid dynamics characteristics of ohmically heated liquid whole egg in the literature. The change of rheological behaviour of the ohmically heated liquid whole egg, across a temperature range of 4-60 A degrees C, was determined by using a concentric rotational viscometer. The ohmic heating was conducted by applying the voltage gradient (20 V/cm) at 50 Hz. The temperature dependency of the electrical conductivity of liquid egg was linear (R (2) = 0.999). The rheological behaviour was found to be shear thinning since power law model had higher regression coefficient and lower chi (2) and root mean square error values than Newtonian model. Ohmically heated liquid whole egg exhibited higher degree of thixotropic index indicating the occurrence of the protein denaturation at 60 A degrees C. The flow behaviour of liquid whole egg in the continuous ohmic heating system was predicted as laminar (GRe range of 87.59-538.87) for the mass flow rate range of 0.0056-0.0166 kg/s. The friction factors and pressure losses in the system in those mass flow rates were also assessed. The result of this study will give necessary information on flow characteristics of liquid whole egg for the modelling, designing and the scaling up of the continuous ohmic heating systems for pasteurisation of liquid egg products

Freezing time prediction for partially dried papaya puree with infinite cylinder geometry

WOS: 000280620700017Dehydrofreezing which is the drying of foods to intermediate moisture content and subsequent freezing has the advantages of lowering the transportation costs due to reduced weight and improved texture. The available empirical equations for freezing time prediction and the experimental data on thermo-physical properties are for fresh produce. Some of these empirical equations were used to predict the freezing times of papaya puree infinite cylinders with initial moisture contents similar to 52% to similar to 91%. The accuracies of these methods to predict the freezing times for final center temperatures of -10 degrees C and -18 degrees C were discussed. The most accurate methods for fresh and partially dries papaya puree were suggested. (C) 2010 Elsevier Ltd. All rights reserved