Nedim Albayrak - Academia.edu (original) (raw)

Papers by Nedim Albayrak

DergiPark (Istanbul University), Aug 26, 2022

DergiPark (Istanbul University), Aug 30, 2022

Cellulose acetate ultrafiltration membranes (CAs) were modified by plasma polymerization (PP) of ... more Cellulose acetate ultrafiltration membranes (CAs) were modified by plasma polymerization (PP) of ethylenediamine (EDA) to prepare extremely hydrophilic nanofiltration membranes. Low-Frequency (LF) and Radio-Frequency (RF) excitations were used for this purpose. The contact angle results showed that the grafted amino groups caused great increase on the polar nature of the CAs studied. The best treatment results were obtained at 120 W and 10 min. for LF-modified CAs and 80 W and 30 min. for RFmodified CAs. A complete and permanent hydrophilic modification of a CA is achieved by LF plasma treatment while polymer layer deposited by RF plasma was not as stable as expected. Therefore, only LF-modified CAs were characterized in details by Fourier Transform InfraRed (FTIR) spectroscopy with Horizontal Attenuated Total Reflection (HATR) attachment and Scanning Electron Microscopy (SEM). This study illustrates the importance of selecting the right plasma system and parameters for cellulose ac...

Ozet Lipaz aktivitesinin spektrofotometrik yontemle olculmesinde p-nitrofenol esterleri tercih ed... more Ozet Lipaz aktivitesinin spektrofotometrik yontemle olculmesinde p-nitrofenol esterleri tercih edilmektedir. Yontem, bu substratlardan lipaz hidrolizi ile ac›k sar› renkli p-nitrofenol ( pNP) oluflturulmas›na dayanmaktad›r. Bu cal›flmada, lipaz aktivite olcumunde kullan›lan p-nitrofenil propiyonat ( pNPP) substrat›n›n kararl›l›¤›na ve pNP urununun ›fl›k sourmas›na cevresel koflullar›n etkisi incelenmifltir. Bekletme s›cakl›¤› veya suresi artt›kca, daha fazla oranda pNPP'nin kendiliinden parcaland›¤› gorulmufltur. On gunluk bir depolama sonunda, 4° C'ye k›yasla 20° C'de 10 kat› oran›nda pNPP (0.512 mM) kendiliinden parcalanm›flt›r. Birbirini takip edecek flekilde 30, 60 ve 95° C'lerde s›ras›yla 90, 20 ve 5 dakika inkubasyon sureleri, dakikada 0.0014, 0.0154 ve 0.0456 absorbans art›fllar›na neden olmufltur. Ote yandan, oluflan pNP urununun 400nm civar›nda gosterecei absorbans deeri pH 6-8 aral›¤›nda ortam pH's›na oldukca duyarl› iken; tampon kapasitesi artt›kca (0....

Enzyme Microb Technol, 2002

Immobilization of Aspergillus oryzae -galactosidase on cotton cloth activated with p-toluenesulf... more Immobilization of Aspergillus oryzae -galactosidase on cotton cloth activated with p-toluenesulfonyl chloride (tosyl chloride) was studied. Enzyme immobilization on the tosylated cotton followed a nucleophilic substitution mechanism as evidenced by UV spectra. NaOH mercerization before tosylation and adding pyridine at a tosyl (g)/pyridine (ml) ratio of 0.2–0.4 increased the final activity of the immobilized enzyme by six-fold. The optimal pH for enzyme immobilization was found to be 4.5. Among different fibrous matrices tested, the knitted cotton cloth showed the highest immobilized enzyme activity. About 50 mg enzyme was immobilized onto each gram of cotton cloth with a protein coupling efficiency of ∼85% and enzyme activity yield of ∼55%. The immobilized enzyme had half-life of ∼50 days at 50 ◦C, and more than 1 year at 40 ◦C, an improvement of 25–28-fold as compared to free enzyme. The enzyme immobilized on cotton cloth can be used in a plug-flow reactor for continuous production of galacto-oligosaccharides (GOS) from lactose. The reactor performance was stable, and there was no loss in enzyme activity at 40 ◦C for the 15-day period studied. The immobilized enzyme also showed same pattern and level of GOS formation from lactose as those from free enzyme reaction, indicating that the reaction kinetics was not affected by immobilization and there was no significant diffusion limitation in the immobilized enzyme reactor. The method to prepare tosylated cotton cloth for enzyme immobilization is simple, inexpensive, and scaleable for industrial applications. Thus, tosylated cotton cloth can be used as a low cost support for highly active and stable biocatalyst.

Bu calismada, bazi toprak ve su orneklerinden amilolitik bakteri ve mayalar izole edilerek, bunla... more Bu calismada, bazi toprak ve su orneklerinden amilolitik bakteri ve mayalar izole edilerek, bunlarin amilaz enzimlerinin ozellikleri arastirilmistir. Calismalarda izole edilen 10 maya ve 49 bakteri izolatindan 17 bakterinin amilolitik aktivite gosterdigi anlasilmistir. Sivi ve kati ortamlarda yapilan amilolitik aktivite olcumlerinde: dogal sicak su ve toprak orneklerinden izole edilen bakterilerin, digerlerine kiyasla, daha fazla aktivite gosterdikleri ve yuksek aktivite gosteren izolatlarin cogunun Bacillus cinsine ait oldugu belirlenmistir. Sicak su kaynagindan izole edilen B. subtilis 5a-2 susunun; maya ozutu-pepton-nisasta besiyerinde (YPS Broth) 40. saatte 24 U/ml a-amilaz ve 32. saatte 13 U/ml ile en yuksek pullulanaz aktivitesine erismistir. Ayni bakterinin amilaz aktivitesine etkisi arastirilan karbohidratlardan, mono- ve disakkaritlerin onemli bir etkisibulunmazken, dekstrin' in en etkili karbohidrat oldugu saptanmis ve ortamda dekstrin kullanilmasi ile amilaz aktivitesi 36 u/ml'ye ulasmistir. Termostabilitesi ve sicaklik optimumu arastirilan Bacillus subtil is 5a- 2 a-amilazi; 50°C de en yuksek aktivite gostermis, 50 ve 90°C sicaklik araliginda aktivite degeri yaklasik %90'in ustunde bulunmustur. Pullulanaz ise 60°C 'de en yuksek aktiviteye erismis olup 60 ve 90°C sicaklik arali ginda aktivite degeri yaklasik %95'in ustunde bulunmustur. Sicaklik stabilitelerinin saptanmasi amaciyla 100CC deki su banyosunda 2 saat inkubasyon sonunda; a-amilaz aktivitesinde %23, pullulanaz aktivitesinde ise % 5 azalma olmustur. Ayni bakterinin a-amilazinin pH 5 ve pullulanazinin pH 4-6 arasinda maksimum aktivite gosterdigi saptanmistir. Elde edilen ham enzim ekstrakti +4°C 'de 4 gun bekletildiginde toplam aktivitede % 5 'lik bir azalma gozlenmistir. Abstract In this study, amylolytic yeasts and bacteria strains were isolated and identified from different soil and water samples and determined some specifications of their amylolytic enzymes. From the samples, 10 yeasts and 49 bacteria strains were isolated, but only 17 bacteria showed amylolytic activity. Isolated amylolytic bacteria were clasified according to their total amylolytic activity on a liquide and a solid media. As a result, a Bacillus subtilis 5a-2 from hot spring sample and some other Bacillus strains from soil showed the highest activity. Hot-spring isolate, Bacillus subtilis 5a- 2 showed 24 U/ml a-amylase activity at 40. hours and 13 U/ml pullulanase activity at 32. hours as it is maximum on the YPS Broth.IV The effects of different C-sources on amylase activity were tested and dextrin was found to be the most effective carbohyrates with 36 U/ml of total activity. Thermostability and optimum temperature of a-amylase of Bacillus subtil is 5a-2 was determined. It was shown that the highest activity at 50°C and between 50°C-90°C the activity was as high as over 90% approximately. The pullula- nase activity has a maximal at 60°C and between 60°-90°C the activity was over 95% approximately, a-amylase has shown an activity of 77% and pullulanase 95 % at the end of incubation for 2 hours in a water bath of 100 °C. Optimum pH was 5 for a-amylase and pH 4-6 for pullulanase. Crude enzyme solution lost 5 % of their total amylase activity after 4 days at +4°C.

Biofuels - Status and Perspective, 2015

p-Nitrophenol alconate esters are preferred substrates for spectrophotometric measurement of lipa... more p-Nitrophenol alconate esters are preferred substrates for spectrophotometric measurement of lipase activity. The method relies on lipolytic release of chromogenic p-nitrophenol (pNP) from the substrates. The study aimed to investigate susceptibility of p-nitrophenyl propionate (pNPP) substrate against non-enzymatic hydrolysis and absorptivity of pNP under various conditions. In general, greater amounts of pNPP were self-hydrolyzed upon increases in storage temperature or duration. Compared to refrigeration temperature, the storage at room temperature for 10 days resulted in ten-fold increase in spontaneous hydrolysis from 0.512 mM pNPP solution. Upon sequential incubation at 30, 60 and 95° C for the corresponding durations of 90, 20 and 5 minutes, the rates of non enzymatic hydrolysis were 0.0014, 0.0154 and 0.0456 absorbans per min, respectively. pNP product absorbans at 404 nm was strongly affected by pH between 6 and 8. Also, increasing buffer capacity from 0.1 to 1.0 M resulted...

Journal of Membrane Science, 2010

The aim of this study is to illustrate the low-pressure plasma modified cellulose acetate (CA) me... more The aim of this study is to illustrate the low-pressure plasma modified cellulose acetate (CA) membranes can display a fractionation capability that can be of major importance for the operation of continuous enzymatic membrane reactors. For this purpose, low-frequency ( ...

Colloids and Surfaces B: Biointerfaces, 2012

In this study, cotton terry cloth fibrils were coated with 0.2% polyethyleneimine (PEI). Lipases ... more In this study, cotton terry cloth fibrils were coated with 0.2% polyethyleneimine (PEI). Lipases from Candida antarctica A (CALA) and Thermomyces lanuginosus (TL) were immobilized on this support through adsorption followed by cross-linking with 0.2% glutaraldehyde. PEI-enzyme aggregates formation and growth of aggregates on cotton cloth fibrils lead to multilayer immobilization of the lipases. PEI and lipase was mixed to form PEI-enzyme complex/aggregate. The highest amount of enzyme precipitate was obtained at the PEI to enzyme ratio of 1/20-1/40 for both lipases. The effect of pH was also investigated for aggregates formation. The results showed that when pH values were below 8, aggregation and precipitation were not occurred for C. antarctica A lipase. However, pH did not affect PEI-enzyme aggregate formation for T. lanuginosus lipase. Immobilized enzyme amount was approximately 180 mg/g support and 200 mg/g support for T. lanuginosus and C. antarctica A lipases, respectively. Effect of the reaction temperature on the relative activity of the free and immobilized lipases at various temperature (30-80 • C) was studied. It was found that immobilization had no effect on the optimum temperature and it was 60 • C for both free and immobilized enzymes. The effect of operational and storage stability on activity of free and immobilized lipases were also investigated. Immobilized lipases exhibited that they could be stored at room temperature with a little activity lost during 28 days.

Catalysis Communications, 2008

Kluyveromyces lactis was covalently immobilized onto a mPOS-PVA, using glutaraldehyde as activati... more Kluyveromyces lactis was covalently immobilized onto a mPOS-PVA, using glutaraldehyde as activating agent and its properties were evaluated. The enzymatic water insoluble derivative displayed the same optimum pH (6.5) and optimum temperature (50°C) of the soluble enzyme. The apparent K app m and activation energy for both soluble and immobilized enzyme derivative were found to be not significantly different. The mPOS-PVA b-galactosidase preparation presented a higher operational and thermal stability than the soluble enzyme. This immobilized b-galactosidase also was effective in hydrolyzing lactose from milk. Hence, one can conclude that mPOS-PVA is an attractive and efficient support for b-galactosidase immobilization.

Biotechnology Progress, 2002

The production of galacto-oligosaccharides (GOS) from lactose by Aspergillus oryzae-galactosidase... more The production of galacto-oligosaccharides (GOS) from lactose by Aspergillus oryzae-galactosidase immobilized on cotton cloth was studied. A novel method of enzyme immobilization involving PEI-enzyme aggregate formation and growth of aggregates on individual fibrils of cotton cloth leading to multilayer immobilization of the enzyme was developed. A large amount of enzyme was immobilized (250 mg/g support) with about 90-95% efficiency. A maximum GOS production of 25-26% (w/w) was achieved at near 50% lactose conversion from 400 g/L of lactose at pH 4.5 and 40°C. Tri-and tetrasaccharides were the major types of GOS formed, accounting for about 70% and 25% of the total GOS produced in the reactions, respectively. Temperature and pH affected not only the reaction rate but also GOS yield to some extend. A reaction pH of 6.0 increased GOS yield by as much as 10% compared with that of pH 4.5 while decreased the reaction rate of immobilized enzyme. The cotton cloth as the support matrix for enzyme immobilization did not affect the GOS formation characteristics of the enzyme under the same reaction conditions, suggesting diffusion limitation was negligible in the packed bed reactor and the enzyme carrier. Increase in the thermal stability of PEI-immobilized enzyme was also observed. The half-life for the immobilized enzyme on cotton cloth was close to 1 year at 40°C and 21 days at 50°C. Stable, continuous operation in a plug-flow reactor was demonstrated for about 3 days without any apparent problem. A maximum GOS production of 26% (w/w) of total sugars was attained at 50% lactose conversion with a feed containing 400 g/L of lactose at pH 4.5 and 40°C. The corresponding reactor productivity was 6 kg/L/h, which is several-hundred-fold higher than those previously reported.

Bioscience, Biotechnology, and Biochemistry, 2001

Biochemical Engineering Journal, 2010

In this study, Aspergillus oryzae β galactosidase was immobilized on concanavalin A layered calci... more In this study, Aspergillus oryzae β galactosidase was immobilized on concanavalin A layered calcium alginate-cellulose beads as a bioaffi nity support. Immobilized enzyme showed a remarkable broadening in temperature-activity profi les as compared to the native enzyme and exhibited 65% activity in the presence of 5% galactose. Michaelis constant (K m) was 2.57 mM and 5.38 mM for the free and the immobilized β galactosidase, respectively. Crosslinked β galactosidase showed greater catalytic activity in the presence of Mg 2+ and was more stable during storage at 4°C for 6 weeks. Immobilized enzyme hydrolyzed 67% lactose in milk in 8 h and 85% lactose in whey in 9 h in the stirred batch process at 50 o C. The continuous hydrolysis of lactose by crosslinked β galactosidase in spiral bed reactor exhibited 93% and 88% hydrolysis of lactose at fl ow rate of 20 ml/h and 30 ml/h, after 1 month operation, respectively.