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Öğe Adsorption Isotherm and Kinetic Modelling of ?-Galactosidase Immobilization onto a Basic Resin (Duolite A568)(Asian Journal Of Chemistry, 2011) Gurdas, Sevim; Gulec, Haci Ali; Mutlu, MehmetThis study aimed to determine adsorption characteristics of Aspergillus oryzae beta-galactosidase onto a basic resin Duolite A568. The experimental data were analyzed by the Langmuir and Freundlich isotherm to describe the adsorption equilibrium. The equilibrium data fitted well with the Langmuir model which confirmed that the Duolite A568 was favourable for adsorption of P-galactosidase enzyme under conditions studied. The maximum adsorption capacity was found to be (5.1 +/- 0.49) x 10(-2) mg/g at 35 degrees C. The kinetic data were fitted. to pseudo-second-order kinetic model of Ho by linear and non-linear regression methods. The enthalpy change (Delta H degrees), the entropy change (Delta S degrees) and the Gibb's free energy change (Delta G degrees) for the:sorption processes were calculated to be 15.5 kJ/mol, 30.4 J/mol K and -9.4 kJ/mol, respectively. The positive Delta H degrees value indicated that the adsorption process was endothermic. Delta G degrees and Delta S degrees values showed that adsorption process occurred by physical mechanism and spontaneously.Öğe Atmospheric pressure plasma jet treatment of wheat straw for improved compatibility in epoxy composites(Wiley, 2018) Huner, Umit; Gulec, Haci Ali; Huner, Irem DamarThe aim of this study was to investigate the effects of an atmospheric-pressure gas plasma jet treatment on the interior and exterior surface characteristics of wheat straw and on the mechanical properties of epoxy composites reinforced with wheat straw. Dry air was used as the process gas in the plasma system. A distance between the nozzle and the substrate surface (DNSS) of 35mm was determined as the most effective parameter enabling remarkable decreases in the gamma(p)(S) (surface energy) values of both the interior and exterior surfaces of virgin wheat straw. Increased intensities of the peaks related to carbon-rich species and 11% to 43% decreases in the oxygen/carbon ratios on the surfaces confirmed the more hydrophobic nature of the plasma-treated wheat straw. A further increase in the DNSS decreased the effectiveness of the plasma treatment, while a decrease in the DNSS caused an inverse effect on the gamma(p)(S) value, probably due to the etching effect of the plasma action, which was supported by the atomic force microscopy analysis. The overall results indicated that the increased hydrophobicity and valley-like occurrences without sharp pits created by the plasma action improved the compatibility of the wheat straw with the epoxy matrix, which contributed to superior mechanical properties of the composites. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45828.Öğe Clarification of Apple Juice Using Polymeric Ultrafiltration Membranes: a Comparative Evaluation of Membrane Fouling and Juice Quality(Springer, 2017) Gulec, Haci Ali; Bagci, Pelin Onsekizoglu; Bagci, UfukThe aim of this study was to evaluate the performance of three different commercial polymeric ultrafiltration (UF) membranes during clarification of raw apple juice, comparatively. The influence of membrane pore size, roughness, and hydrophobicity on flux profile and fouling was investigated. The initial flux was simultaneously decreased at the beginning of the process, and quite steady flux was obtained in the membranes with rougher surface and more hydrophobic nature. As the pore size and hydrophobicity increased, the reversible fouling became the major resistance, while cake formation was more prominent for the membranes with narrower pore size. The overall quality results revealed that the main quality characteristics of the raw juice can be better retained by using the membranes that have higher resistance to fouling.Öğe The combined effect of probiotic cultures and incubation final pH on the quality of buffalo milk yogurt during cold storage(Wiley, 2018) Akgun, Abdullah; Yazici, Fehmi; Gulec, Haci AliThe combined effects of starter culture type (SCT) and incubation final pH (IFpH) on the physicochemical and organoleptic properties of buffalo milk yogurt containing 3g100g(-1) milk fat were investigated throughout 20days of storage at 4 degrees C. The postacidification kinetics fitted to zero-order reaction for all buffalo milk yogurt samples. The reaction rate constants of the buffalo milk yogurt samples containing YC-X11, ABY-2, and ABT-4 cultures were 0.010, 0.007, and 0.004g100g(-1)day(-1), respectively. Regardless of the IFpH, the absence of Lactobacillus delbrueckii subsp. bulgaricus in the starter culture increased the syneresis. L*, a*, and b* values were not affected by the IFpH and the SCT. ABY-2 culture increased the amount of organic acids during cold storage in comparison with the YC-X11, while its effect on the proportions of saturated and unsaturated fatty acids was not significant. The results of sensory evaluation revealed that a more acceptable buffalo milk yogurt can be manufactured by using probiotic ABY-2 culture.Öğe Concentration of whey proteins by ultrafiltration: Comparative evaluation of process effectiveness based on physicochemical properties of membranes(Elsevier Sci Ltd, 2020) Damar, Irem; Cinar, Kadir; Gulec, Haci AliPermeate flux, solute rejection, membrane fouling and permeate flux recovery in ultrafiltration (UF) acid bovine cheese whey was investigated for RC70PP (regenerated cellulose acetate), ETNA10PP (composite fluoro polymer) and GR73PP (polyethersulphone) commercial UF membranes (all 10 kDa nominal pore size). Pore morphology dominantly affected water permeability; active layer porosity affected intrinsic membrane resistance. Membrane roughness was the main factor in irreversible fouling resistance; the high roughness of ETNA10PP increased the rejection of the common whey proteins and lactose. A positive surface free energy of interaction of RC70PP resulted in comparable low fouling propensity regardless of the zeta-potential. The surface charge of two hydrophobic membranes (ETNA10PP and GR73PP) significantly affected fouling resistance. The recovery ratio of initial permeate flux after cleaning was directly related to the membrane hydrophilicity. The RC70PP membrane offered much better efficiency for the concentration of whey proteins due to its high antifouling performance despite its poor selectivity. (C) 2020 Elsevier Ltd. All rights reserved.Öğe Coupling reverse osmosis and osmotic distillation for clarified pomegranate juice concentration: Use of plasma modified reverse osmosis membranes for improved performance(Elsevier Sci Ltd, 2019) Bagci, Pelin Onsekizoglu; Akbas, Meryem; Gulec, Haci Ali; Bagci, UfukIn this study, a low pressure nitrogen plasma (LPNP) activation was implemented to modify the surface characteristics of a commercial thin film composite (TFC) polyamide reverse osmosis (RO) membrane. The free energy of interaction (Delta G(iwi)) results showed that the hydrophobic nature of untreated TFC RO membrane became considerably hydrophilic with the effect of LPNP treatment. Among various plasma powers and exposure times tested, a general decreasing trend was observed for the water contact angle with increasing plasma duration, reaching a minimum of 13.2 +/- 0.8 degrees for 90 W at 15 min. A remarkable increase in water flux of the LPNP modified RO membrane was observed throughout the RO process, which promoted higher soluble solids content (SSC) values in the concentrated juice at the same period of time with the plain one. The higher SSC values achieved by the modified RO membrane enabled 30% time-saving during further osmotic distillation process.Öğe Effect of gas type and application distance on atmospheric pressure plasma jet-treated flax composites(Sage Publications Ltd, 2017) Huner, Umit; Gulec, Haci Ali; Damar Huner, IremThis study reports on the effect of atmospheric pressure plasma jet treatment on the flax fiber and flax-reinforced epoxy. The atmospheric pressure plasma jet was carried out by using four different gasses and various application distance in the range of 30-40mm. The treatments were investigated by means of contact angle, attenuated total reflectance-Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy and mechanical tests. Depending on the application parameters, the rate of increase in water contact angle varied from 49% to 92%. While atomic force microscopy and scanning electron microscopy investigations exhibited changed surface morphology, FTIR presented interactions at the molecular level. Improvement in mechanical properties was obtained for all atmospheric pressure plasma jet applications, while the increase in tensile strength in the composite material reached 180%, and the increase in flexural strength was 140%. The atmospheric pressure plasma jet method, according to similar plasma applications, came to the forefront with the short processing time and the intensity of the effect it created.Öğe Effect of reduced fat content on the physicochemical and microbiological properties of buffalo milk yoghurt(Elsevier, 2016) Akgun, Abdullah; Yazici, Fehmi; Gulec, Haci AliThe objective of this study was to investigate the effect of reduced fat content in buffalo milk on textural, chemical and microbiological characteristics of plain buffalo yoghurt during storage at 4 degrees C. Four yoghurt samples were manufactured with different fat ratios (1.5-6 g/100 g) and analysed on the first, 10th and 20th days of storage. Increasing the fat content of the yoghurt increased the La value, viscosity, and cohesiveness and decreased the a* value, syneresis, hardness, and springiness. Fat reduction did not cause any significant changes in the adhesiveness, gumminess, titratable acidity, b* value, and Streptococcus thermophilus population of buffalo yoghurt samples. Storage time had no significant effect on adhesiveness, springiness, and L* value of buffalo yoghurts. A decrease in S. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus populations during storage was detected. It was concluded that more acceptable buffalo yoghurt could be produced from milk with 3 g/100 g fat. (C) 2016 Elsevier Ltd. All rights reserved.Öğe Enzymatic synthesis of prebiotic carbohydrates from lactose: Kinetics and optimization of transgalactosylation activity of ?-galactosidase from Aspergillus oryzae(Wiley, 2020) Cinar, Kadir; Gunes, Gurbuz; Gulec, Haci AliThe aim of the study was to analyze galactooligosaccharide (GOS) synthesis catalyzed by beta-galactosidase from Aspergillus oryzae by applying experimental data to optimization and kinetic parameter estimation methods. The apparent kinetic parameters were determined in varying initial lactose concentrations by using six-step, 11-parameter GOS synthesis mechanism. The results revealed that GOS yield was mainly dependent on initial lactose concentration; on the other hand, all of the reaction parameters affected the required time to achieve maximum GOS yield (TMGY) significantly. The values of 32 degrees Brix, 36.8 degrees C, and 8.32 U/g lactose solution were determined as the optimum reaction experimental set which offers 26.73% GOS yield and 369.82 min TMGY. The increased enzyme-galactose complex dissociation ratio (k(3)/k(-3)) with decreasing initial lactose concentration resulted to low GOS productivity although GOS production/GOS dissociation rate ratio (k(4)/k(-4)) increased with decreasing initial lactose concentration. This result signified that hydrolysis characteristics dominated the reaction medium at low initial lactose concentration. The role of monosaccharide inhibition became important on GOS synthesis for increasing initial lactose concentration. Practical Applications The proposed study deals with investigation of the effects of initial lactose concentration, enzyme concentration, and temperature on enzymatic synthesis of galactoligosaccharide (GOS) from lactose by beta-galactosidase from Aspergillus oryzae (beta gAO) and estimation of apparent kinetic rate constants of the reaction which is important to design of futuristic strategies improving the GOS yield. Low GOS yield is the main concern of the prebiotic food industry due to thermodynamic and kinetic realities of the reaction. Deeper evaluation of the reaction mechanism will contribute valuable data to the partners in the scope of designing more productive engineering methods.Öğe Fouling behavior of poly(ether)sulfone ultrafiltration membrane during concentration of whey proteins: Effect of hydrophilic modification using atmospheric pressure argon jet plasma(Elsevier Science Bv, 2017) Huner, Irem Damar; Gulec, Haci AliThe aim of the study was to investigate the effects of hydrophilic surface modification via atmospheric pressure jet plasma (ApJPls) on the fouling propensity of polyethersulfone (PES) ultrafiltration (UF) membranes during concentration of whey proteins. The distance from nozzle to substrate surface of 30 mm and the exposure period of 5 times were determined as the most effective parameters enabling an increase in Delta G(iwi) value of the plain membrane from (-) 14.92 +/- 0.89 mJ/m(2) to (+) 17.57 +/- 0.67 mJ/m(2). Maximum hydrophilicity and minimum surface roughness achieved by argon plasma action resulted in better antifouling behavior, while the hydraulic permeability and the initial permeate flux were decreased sharply due to the plasma-induced surface cross-linking. A quite steady state flux was obtained throughout the UF with the ApJPls modified PES membrane. The contribution of R-frev to R-t, which was 94% for the UF through the plain membrane, decreased to 43% after the plasma treatment. The overall results of this study highlighted the ApJPls modification decreased the fouling propensity of PES membrane without affecting the original protein rejection capability and improved the recovery of initial permeate flux after chemical cleaning. (C) 2017 Elsevier B.V. All rights reserved.Öğe Hydrophilic modification of poly(ether)sulfone membrane by atmospheric pressure argon jet plasma: pH dependence of ultrafiltration performance and cleaning efficiency(Wiley, 2021) Damar, Irem; Gulec, Haci AliThe studies focused on plasma surface modification of poly(ether)sulfone (PES) ultrafiltration (UF) membrane show its potent effect on antifouling propensity but there are few data on the pH dependence of superior surface character achieved. This study examined UF performance and cleaning efficiency of atmospheric pressure argon jet plasma (AP-AJP) modified PES membrane in whey concentration at various operation pH compared to the plain membrane (UP020). The highest initial permeate flux for the UP020 at pH of 6.4 increased the cake layer formation and the irreversible fouling resistance. The plasma action led to greater intrinsic membrane resistance causing low water permeability compared with the UP020. This effect reduced cake layer resistance despite the fact that the irreversible fouling was more severe at all operation pH. The increase in pH caused to decrease in contribution of fouling to total resistance. For the UP020, the shift in operation pH from acidic point to neutral reduced the recovery in hydraulic permeability after chemical cleaning. The plasma action induced greater cleaning efficiency, which is the most obvious at pH of 6.4. The overall results showed that the AP-AJP may have the potential to maintain profit-making UF process in whey concentration at broad range of pH. Practical Applications In the industrial point of view, cost friendly, and sustainable operation in valorization of whey can be achieved by fouling resistant membranes. Atmospheric pressure argon jet plasma provides extremely hydrophilic character to poly(ether)sulfone membrane. The plasma action decreases fouling resistance and especially cake layer formation. This effect broadens the operating pH of whey without any pre-adjustment and results in easy to clean membrane surfaces.Öğe Immobilization of ?-galactosidase from Kluyveromyces lactis onto polymeric membrane surfaces: Effect of surface characteristics(Elsevier, 2013) Gulec, Haci AliThe aim of this study was to investigate the effects of surface characteristics of plain and plasma modified cellulose acetate (CA) membranes on the immobilization yield of beta-galactosidases from Kluyveromyces lactis (KLG) and its galacto-oligosaccharide (GOS) yield, respectively. Low pressure plasma treatments involving oxygen plasma activation, plasma polymerization (PlsP) of ethylenediamine (EDA) and PlsP of 2-mercaptoethanol were used to modify plain CA membrane surfaces. KLG enzyme was immobilized onto plain and oxygen plasma treated membrane surfaces by simple adsorption. Oxygen plasma activation increased the hydrophylicity of CA membrane surfaces and it improved the immobilization yield of the enzyme by 42%. KLG enzyme was also immobilized onto CA membrane surfaces through amino groups created by PlsP of EDA via covalent binding. Plasma action at 60 W plasma power and 15 min. exposure time improved the amount of membrane bounded enzyme by 3.5-fold. The enrichment of the amount of amino groups via polyethyleneimine (PEI) addition enhanced this increase from 3.5-fold to 4.5-fold. Although high enzyme loading was achived (65-83%), both of the methods dramatically decreased the enzyme activity (11-12%) and GOS yield due to probably negative effects of active amino groups. KLG enzyme was more effectively immobilized onto thiolated CA membrane surface created by PlsP of 2-mercaptoethanol with high immobilization yield (70%) and especially high enzyme activity (46%). Immobilized enzymes on the CA membranes treated by PlsP were successively reutilized for 5-8 cycles at 25 degrees C and enzymatic derivatives retained approximately 75-80% of their initial activites at the end of the reactions. (c) 2012 Elsevier B.V. All rights reserved.Öğe Immobilization of Aspergillus oryzae ?-Galactosidase on Low-pressure Plasma-modified Cellulose Acetate Membrane Using Polyethyleneimine for Production of Galactooligosaccharide(Korean Soc Biotechnology & Bioengineering, 2010) Gulec, Haci Ali; Gurdas, Sevim; Albayrak, Nedim; Mutlu, MehmetThe aim of this study was to produce galacto-oligosaccharides (GOS) from lactose using beta-galactosidase from Aspergillus oryzae immobilized on a low-pressure plasma-modified cellulose acetate (CA) membrane Specifically, a novel method was developed for multilayer enzyme immobilization involving polyethyleneimine (PEI)-enzyme aggregate formation and growth on a CA membrane A large amount of enzyme (997 mu g/cm(2) membrane) was immobilized with 66% efficiency The K(m) value for the immobilized enzyme was estimated to be 48 mM, which indicates decreased affinity for the substrate, whereas the Vmax value was smaller The immobilized enzyme showed good storage and operational stability The half-life of the immobilized enzyme on the membrane was about 1 month at 30 degrees C and similar to 60 h at 60 degrees C Maximum GOS production of 27% (w/w) was achieved with 70% lactose conversion from 320 g/L of lactose at pH 4 5 and 60 degrees C Trisaccharides were the major types of GOS formed and accounted for about 75% of the total GOS produced Based on these results, immobilized enzyme technology could be applied to GOS production from lactoseÖğe Immobilization of Aspergillus oryzae ?-Galactosidase onto Duolite A568 Resin via Simple Adsorption Mechanism(Springer, 2012) Gurdas, Sevim; Gulec, Haci Ali; Mutlu, MehmetIn this study, a rapid, simple and economic method of enzyme immobilization was developed to hydrolyze lactose. Duolite A568 resin was used for the immobilization of beta-galactosidase via simple adsorption mechanism. The effects of immobilization parameters such as time, pH, and temperature were studied. Immobilization parameters for maximum enzyme activity were estimated at 35 A degrees C temperature, pH 4.5, 5 mg/mL enzyme concentration, and approximately 60 min immobilization time. A significant amount of enzyme was immobilized with high catalytic activity. Enzyme immobilization procedure explained in this study slightly affected the enzyme kinetic. The value of Michaelis constant K (m) for immobilized enzyme was significantly larger, indicating decreased affinity by the enzyme for its substrate. It was observed that both free and immobilized enzyme showed maximum activity at 65 A degrees C reaction temperature. Immobilized beta-galactosidase was significantly more active at all temperatures as compared to its free form. However, optimal pH of immobilized enzyme was slightly affected by immobilization procedure. The optimum pH of immobilized enzyme was shifted up 0.5 unit to a more alkaline value of 6.0 compared to the free enzyme.Öğe Performance enhancement of ultrafiltration in apple juice clarification via low-pressure oxygen plasma: A comparative evaluation versus pre-flocculation treatment(Elsevier Science Bv, 2018) Gulec, Haci Ali; Bagci, Pelin Onsekizoglu; Bagci, UfukThe aim of this study was to improve ultrafiltration (UF) performance during clarification of raw apple juice through surface modification of commercial polysulfone membranes (US100) by low-pressure oxygen plasma treatment (LP-OPlsT). A Plasma power of 90 W and exposure time of 10 min were determined as the most effective parameters enabling an increase in the Delta G(iwi) value of the plain membrane from (-) 25 +/- 2 mN m(-1) to (+) 30 +/- 1 mN m(-1). Improved hydrophilicity achieved by LP-OPlsT remarkably enhanced the performance of US100 throughout the clarification of raw apple juice without the need of an additional pre-flocculation step. While R-frev (86%) was the dominant resistance controlling the fouling during UF of raw apple juice through the plain membrane, the contribution of R-frev to R-t decreased to 56% after pre-flocculation step. LP-OPlsT further decreased this ratio, up to 46%, confirming the charge repulsion between the modified membrane and the foulant particles.Öğe Pomegranate juice concentration through the consecutive application of a plasma modified reverse osmosis membrane and a membrane contactor(Elsevier, 2020) Bagci, Pelin Onsekizoglu; Kahvecioglu, Hayriye; Gulec, Haci Ali; Bagci, UfukA low-pressure nitrogen plasma (LPNP) modified commercial thin-film composite membrane was used for pre-concentration of the clarified pomegranate juice (C-PJ) by reverse osmosis (RO). Pre-concentrates then submitted to osmotic distillation (OD) for further concentration. The productivity of the integrated membrane process was benchmarked considering both the performance and the final product quality. The modified RO membranes had great potential for shortening duration of consecutive concentration process, enabling up to 36% time saving during concentration of the C-PJ from 15.6 degrees Brix to >65 degrees Brix. Aroma losses observed in stand-alone OD are also prevented by shortening the duration of OD. Lower retention of malic acid, gallic acid, glucose, and fructose was observed due to the increased permeability following LPNP modification. However, these losses did not seem to affect the total acidity, total phenolic content, and total antioxidant activity of the concentrates obtained. The total color change was also in the range of barely noticeable values. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.Öğe Production of concentrated whey beverage by osmotic membrane distillation: Comparative evaluation of feed effect on process efficiency and product quality(Elsevier Sci Ltd, 2021) Gulec, Haci Ali; Cinar, Kadir; Bagci, Ufuk; Bagci, Pelin OnsekizogluReconstituted whey powder (RCW), whey released after rennet-coagulation (PW) and microfiltration permeate of skim milk (IW) were used to produce concentrated beverage by osmotic membrane distillation (OMD). Effect of feed type on OMD performance and on final quality were evaluated. The use of IW not only promoted the greatest initial permeate flux but also reduced the operation time of OMD needed to reach 15.7 +/- 0.4 Brix, as compared with PW and RCW. Based on mineral and amino acid intake, the concentrated IW corresponded to 50 +/- 3% and 76 +/- 5% of equal amount of skim milk, respectively. While IW beverage was a good source of isoleucine, PW beverage provided adequate intake of valine besides leucine and isoleucine. Along with the better process performance, the use of IW in OMD resulted in obtaining plain concentrated whey beverage having comparable nutritive value with the PW and the RCW, and better clarity. (c) 2021 Elsevier Ltd. All rights reserved.Öğe Recovery of Phenolic Compounds from Pomegranate Peels by Sequential Processes of Water Base Extraction and Ultrafiltration: Modelling of the Process Efficiency and Fouling Analysis(Springer, 2022) Uca, Esra; Gulec, Haci AliThe goal of this study was to recover of phenolic compounds from pomegranate peels (Cortex Granati fructuum) with high yield by sequential processes of water base extraction and ultrafiltration (UF). The effects of transmembrane pressure (TMP), process temperature (T) and initial total phenolic content (TPC) of feed on UF performance were modelled by Box-Behnken method. The optimum conditions were TPC of feed of 524 mg gallic acid L-1 extract, T of 37 degrees C and TMP of 150 kPa providing the maximum 8.5-fold increase in TPC and the acceptable 20% decrease in initial permeate flux. The TMP was the most significant parameter affecting the solute rejection and the membrane fouling. Increase in the TMP caused to threefold increase in the cake layer resistance while the irreversible fouling resistances were negligible for all the operations. As a result, the UF process through the extremely hydrophilic membrane provided efficient phenolic recovery with membrane fouling at a reasonable level can serve more profit-making process to the industry.
