Browsing by Author "Icier, F"

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    Changes on rheological properties of pomegranate (Punica granatum L., cv. Hicaznar) juices during concentration process
    Cevik, M; Sabanci, S; Icier, F; Yildiz, H
    The investigation of the changes on rheological properties during evaporation process could diminish the severe effects of thermal processing at any individual soluble solids content. In this study, the rheological properties of pomegranate juices at different soluble solids content (20, 30, 40 and 50 %) during concentration process applied by using the rotary evaporator were determined. Rheological measurements were conducted in the range of 0-264 s(-1) shear rates by using the concentric cylinder type viscometer. It was found expectedly that apparent viscosity increased as the soluble solids content increased. The apparent viscosity was 0.0024 +/- 0.0001 Pa. s for raw pomegranate juices (15.73 +/- 0.30 % soluble solids) while it increased to 0.01342 +/- 0.0003 Pa. s for the concentrated juice having 50 % soluble solids contents. Four different rheological models were applied to find the suitable model best fitting the experimental data; Newton model, Power Law model, Bingham model and Herschel-Bulkley model. The statistical criteria having highest regression coefficient, lowest root mean square error and lowest chi-square were chosen for selection of best model for fitting. It was determined that the Power law model was best described the experimental shear stress-shear rate relation for pomegranate juices at different concentrations. It was predicted that the consistency coefficient of pomegranate juice increased from 0.005 Pa.s(n) to 0.013 Pa. sn as the soluble solid content was increased from 20 % to 50 %. The rheological data obtained in this study could serve valuable data for calculation of changes in flow behaviors of pomegranate juice in pumping systems depending of their concentration.
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    Effects of electrical pretreatment conditions on osmotic dehydration of apple slices: Experimental investigation and simulation
    Yildiz, H; Icier, F; Eroglu, S; Dagci, G
    Electrical pretreatments at 9 different conditions consisting of the combination of 3 different voltage gradients (20, 27, and 32 V/cm) and 3 different application times (10, 20, and 30 s) were applied on apple slices. Apple slices were osmotically dehydrated in 50% sucrose solution at 40 degrees C until their total dry matter content (TDM) reached to 40%. The effect of pretreatment conditions on the change of water loss and solid gain during osmotic dehydration was investigated, and effective diffusion coefficients were determined. The time needed to reach up to 40% TDM content was predicted by using the numeric solution of unsteady state mass transfer equations and diffusion coefficients via MATLAB code written. The electrical pretreatments reduced the osmotic dehydration time by in the range of 26-64%. The final water and solid distributions of apple slices were simulated in ANSYS. Modeling and simulation results were in good agreement with experimental data (p < 0.05). Industrial relevance: Since the electrical pretreatment both shortens the osmotic dehydration time and increases the water removed per unit energy used, its application prior to osmotic dehydration processes in the commercial productions will be economical. The proposed modeling and simulation approach for assessment of the effects of electrical pretreatments on osmotic dehydration characteristics may provide valuable information on the scaling up of these conditions in the industrial scale systems. (C) 2016 Elsevier Ltd. All rights reserved.
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    CHANGES IN β-CAROTENE, CHLOROPHYLL AND COLOR OF SPINACH PUREE DURING OHMIC HEATING
    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), beta-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 beta-carotene contents (P < 0.05). This increase could be caused by the possible enhancing effect of ohmic heating on beta-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 beta-carotene. PRACTICAL APPLICATIONS The present study suggests that ohmic heating could be used to heat the spinach puree faster than conventional heating by adjusting voltage gradient. Moreover, this treatment resulted in high retention of color attributes. In this study, detailed information was given about the effects of ohmic heating parameters such as temperature, voltage gradient and holding time on chlorophyll, beta-carotene and color values of spinach puree. There are no published data in the open literature about effects of ohmic heating on beta-carotene and chlorophyll, to the authors' knowledge. These data could be used in designing of ohmic heating units for functional foods.
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    Peroxidase inactivation and colour changes during ohmic blanching of pea puree
    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 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.
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    Ohmic and Conventional Heating of Pomegranate Juice: Effects on Rheology, Color, and Total Phenolics
    Yildiz, H; Bozkurt, H; Icier, F
    Ohmic heating is an alternative fast-heating method especially for liquid foods. In this study, pomegranate juice samples, prepared by two different extraction methods, were heated ohmically by matching the same thermal history, with that of the conventional method. The ohmic heating application was conducted by changing the voltage gradient (10-40 V/cm) at 50 Hz. The samples were heated from 20 degrees C to 90 degrees C and held at 90 degrees C for different treatment times (0, 3, 6, 9 or 12 min). Although rheological properties, color, and total phenolic content (TPC) values changed at the initial heating up period, there were no significant changes during holding period (p<0.05). Non-Newtonian (power law) rheology model had higher regression coefficient than Newtonian model, and the extraction method affected the consistency of pomegranate juice samples (p<0.05). Color values of juice extracted from arils (APJ) was better than that of juice extracted from whole fruits (PPJ), as PPJ contained higher amount of TPC (p<0.05). Since the heating method did not affect the rheological properties, color, and TPC values, it could be said that there was no electrical effect rather than thermal effects during ohmic heating of pomegranate juice. Ohmic heating could be recommended as an alternative fast-heating method for fruit juices.
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    Ohmic heating assisted vacuum evaporation of pomegranate juice: Electrical conductivity changes
    Icier, F; Yildiz, H; Sabanci, S; Cevik, M; Cokgezme, OF
    A novel electrical heating method, named as ohmic heating, was successfully integrated to vacuum evaporation system, and pomegranate juice was concentrated until its total soluble dry matter content reached to 40% by applying three different voltage gradients (7.5, 10, and 12.5 V/cm) at 180 mm Hg absolute pressure in this system. Total evaporation times were determined as 152, 78, and 53 min at the voltage gradients of 7.5, 10, and 12.5 V/cm, respectively. The concentration time of pomegranate juice was shortened about 56% by ohmic heating relative to conventional evaporation. The electrical conductivity values were increased up to reach 25% TSDM for 7.5 V/cm and at 35% TSDM for 10 V/cm, then showed a decreasing pattern. However, it was constant (0.55 0.01 S/m) during evaporation process at 12.5 V/cm. It is recommended that the ohmic heating method could be successfully integrated to vacuum evaporation process to shorten the processing time significantly. Industrial relevance: Ohmic heating has been utilized as alternative method for the purpose of heating, pasteurization, cooking etc., and relatively better products can be obtained by ohmic heating. Nowadays, energy efficient systems are needed in concentrated juice production. The integration of ohmic heating to the conventional vacuum systems could serve the production high quality juice concentrates with efficient use of energy. In present study, ohmic heating assisted vacuum evaporation of pomegranate juice was conducted, successfully. This method decreased the total process time for juice concentration, which is critically important for industrial scale productions. This novel method can be implemented to the fruit juice production lines by taking into account of design characteristics of ohmic systems such as electrical conductivity changes depending on both temperature and total soluble solids concentration. The effects of main process parameter, named as voltage gradient, on electrical conductivity changes during electrical heating assisted evaporation process has been also reported in the present study. (C) 2017 Elsevier Ltd. All rights reserved.
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    Performance analyses for evaporation of pomegranate juice in ohmic heating assisted vacuum system
    Cokgezme, OF; Sabanci, S; Cevik, M; Yildiz, H; Icier, F
    Pomegranate juice having 17.5% total soluble solids (TSS) content was evaporated to 40%TSS by ohmic heating assisted vacuum evaporation (OVE; 7.5 V/cm, 10 V/cm and 12.5 V/cm) and vacuum evaporation (VE) methods. Thermodynamics' first law and second law analyses were conducted for different TSS contents (20-40%) by taking into account of two different control boundaries; in terms of process boundary (PB) and system boundary (SB). Energy efficiency, specific water removal rate (SWRR) and exergy efficiency reached maximum values for 30% TSS content, then it decreased. It was determined that energetic and exergetic efficiencies of SB were lower than those of PB. For the same TSS content, exergy efficiency value increased and improvement potential (IP) value decreased as the voltage gradient increased. Since highest energy consumption (5844.20 +/- 29.89 J) was determined at 40% TSS content for 7.5 V/cm (p < 0.05) this process condition need the improvement most. It can be concluded that OVE method used the energy more efficiently than VE method for the purpose of the concentration of pomegranate juice. (C) 2017 Elsevier Ltd. All rights reserved.
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    Quality characteristics of pomegranate juice concentrates produced by ohmic heating assisted vacuum evaporation
    Sabanci, S; Cevik, M; Cokgezme, OF; Yildiz, H; Icier, F
    BACKGROUND Vacuum evaporation (VE) process is widely utilized in fruit juice evaporation to preserve quality attributes of final product. However, it has some disadvantages such as possible degradation of aroma components or volatile fatty acids due to long process time, and low energy efficiency of process. Pomegranate juice having 17.5% total soluble solid (TSS) content was evaporated to 40% TSS by ohmic heating assisted vacuum evaporation (OVE; 7.5, 10 and 12.5 V cm(-1)) and VE in the present study. The effects of the evaporation methods on pH, titratable acidity and colour values, antioxidant activity (AA), total monomeric anthocyanin (TMA), total phenolic content (TPC), hydroxymethylfurfural (HMF) and invert sugar content of pomegranate juice concentrates were compared. RESULTS The colour properties, TMA, TPC and AA values of pomegranate juice concentrates evaporated by OVE were more influenced than those evaporated by VE. The degradation of sugars was minimized for OVE processes at high voltage gradients (10 and 12.5 V cm(-1)), and HMF content of pomegranate juice concentrated by OVE was lower than VE. CONCLUSION It is thought that electrochemical reactions occurred because of the use of titanium electrodes during the OVE process caused these quality changes in pomegranate juice concentrates having high acidity. Hence, it was concluded that the utilization of relatively more electrochemically inert electrodes should be investigated in further studies to better evaluate the of influence of OVE method on quality attributes of different fruit juices. (c) 2018 Society of Chemical Industry
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    Processing of Fruits and Fruit Juices by Novel Electrotechnologies
    Evrendilek, GA; 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.