Browsing by Author "Baysal T."
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Item Peroxidase inactivation and colour changes during ohmic blanching of pea puree(2006) Icier F.; Yildiz H.; Baysal T.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 °C to 100 °C and held at 100 °C to achieve adequate blanching. The conventional blanching was performed at 100 °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 (R2 = 0.954), which describes closely the reaction kinetics of total colour changes of pea puree for ohmic blanching at 20 V/cm. © 2005 Elsevier Ltd. All rights reserved.Item Effects of alternative current heating treatment on Aspergillus niger, pectin methylesterase and pectin content in tomato(2006) Yildiz H.; Baysal T.The main purpose of using alternative current (AC) heating treatment is to inactivate enzymes and microorganisms. The inactivation of pectin methylesterase (PME) and Aspergillus niger, and the changes in total pectin content by AC heating with different electric field strengths in the range of 36-108 V/cm for different treatment times in tomato fruit were investigated. PME activity decreased with an increase in treatment time at 108 V/cm. However PME activity increased by AC treatment at 48 V/cm for 5 s and at 36 V/cm for 5, 10, 15, and 30 s. compared to untreated control. The highest amount of total pectin was determined as 3.56% at 89 °C by AC treatment at 36 V/cm for 80 s. The A. niger inactivation was increased with increase in electric field strength and increased temperature. The concentration of A. niger (cfu/g) was determined to be <10 at 108, 68, 48, and 36 V/cm electric field strengths for the treatment times of 6, 12, 20 and 30 s, respectively. © 2005 Elsevier Ltd. All rights reserved.Item Color and lycopene content of tomato puree affected by electroplasmolysis(2007) Yildiz H.; Baysal T.Tomato puree was produced using three different breaking methods, namely heating by steam injection, by electroplasmolysis, and combination of both steam injection and electroplasmolysis. In electroplasmolysis, the tomato pulp was treated at the electric field strength of 68 V/cm for 1.5 seconds. L, a, b, a/b, tomato color index, total color difference, chroma difference, hue angle, and lycopene content of purees were measured. Puree samples breaked by electroplasmolysis had better color values and the highest lycopene content. The a/b, tomato color index, and lycopene content of these samples were as 2.00; 49.94 and 273.9 mg/kg, respectively.Item Polyphenoloxidase deactivation kinetics during ohmic heating of grape juice(2008) 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 °C to temperatures of 60, 70, 80 or 90 °C and the change in the activity of polyphenoloxidase enzyme (PPO) was measured. The critical deactivation temperatures were found to be 60 °C or lower for 40 V/cm, and 70 °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 °C was found to be 83.5 kJ/mol. © 2007 Elsevier Ltd. All rights reserved.Item Changes in β-carotene, chlorophyll and color of spinach puree during ohmic heating(2010) Yildiz H.; Icier F.; Baysal T.The spinach puree was heated from 30C to prescribed temperatures (60, 70, 80 or 90C) ohmically and conventionally. Ohmic heating was performed by application of four different voltage gradients in the range of 10-40 V/cm, while conventional heating was conducted at constant temperature in a water bath. Although ohmic heating time required from 30 to 70C was similar for water heating (129 ± 7 s) and ohmic heating by 20 V/cm (127 ± 2 s), faster heating (51 ± 0.5 s) could be obtained as the voltage gradient for ohmic heating increased to 30 V/cm. Ohmic heating caused browning more than conventional water heating for the same temperature range. The effect of voltage gradient applied was not found statistically significant on chlorophyll (total, a and b), β-carotene and color values (L, a, b, Lb/a, Lba, hue angle) (P < 0.05). On the other hand, temperature (60, 70, 80 or 90C) at constant voltage gradient (30 V/cm) affected color values of spinach puree (P < 0.05), whereas holding time (0 and 600 s) at constant temperature increased chlorophyll-a and β-carotene contents (P < 0.05). This increase could be caused by the possible enhancing effect of ohmic heating on β-carotene biosynthesis and formation of chlorophyll derivatives. It was concluded that ohmic heating could be applied to vegetable purees, resulting in high retention of color attributes and β-carotene. © 2009 Wiley Periodicals, Inc.Item Processing of Fruits and Fruit Juices by Novel Electrotechnologies(2012) Evrendilek G.A.; Baysal T.; Icier F.; Yildiz H.; Demirdoven A.; Bozkurt H.Recent demands from consumers for fresh-like quality foods with less and/or no artificial additives have introduced innovative processing technologies. These technologies due to their potential for food processing with preservation of important properties may cause to introduce new products in the market, to improve the competitiveness of the food, to eliminate the use of some artificial food additives, and to reduce energy cost. Pulsed electric fields for microbial and enzyme inactivation, shelf-life extension, moderate electric fields for yield and extraction, and ohmic heating are among these novel technologies that are based on the application of electric current on food materials. It has been well established that these technologies can successfully be applied to different food products. Among all, fruit juices have special importance due to the suitability of their physical properties to be processed by the electrotechnologies. This article covers the fundamentals of these technologies, their current use, research activities, and trends. © 2011 Springer Science + Business Media, LLC.Item Levan production by Zymomonas mobilis in batch and continuous fermentation systems(2014) Silbir S.; Dagbagli S.; Yegin S.; Baysal T.; Goksungur Y.Levan production in batch and continuous fermentation systems by Zymomonas mobilis B-14023 was investigated. The culture medium used in both of the fermentation systems contained sucrose and various organic nitrogen sources. Maximum concentration of levan was produced with yeast extract among the nitrogen sources tested. Response surface methodology was used to investigate the effects of three factors on the concentration of levan in batch cultures of Z. mobilis. Maximum levan concentration was 40.2 g/L and this concentration was reached at the optimum levels of process variables, which were 299.1 g/L initial substrate concentration, 42.3 h incubation time, and initial pH 6.0. Continuous fermentation experiments were done in packed bed bioreactor using Ca-alginate immobilized Z. mobilis cells. The highest levan concentration (31.8 ± 0.21 g/L) was obtained at a dilution rate of 0.14 h-1 while maximum volumetric productivity (6.556 g/(L h)) was obtained at a dilution rate of 0.22 h-1. Increasing the dilution rate resulted in decreased levan and increased residual sugar concentrations. © 2013 Elsevier Ltd. All rights reserved.Item Moderate Electric Treatment Applications on Pomegranate Juice Production: Yield and Physicochemical Properties(Blackwell Publishing Ltd, 2017) Demırdöven A.; Yildiz H.; İçıer 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 Applications: Juice 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. © 2016 Wiley Periodicals, Inc.