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    Öğe
    Immobilization of Aspergillus oryzae ?-galactosidase on low-pressure plasma-modified cellulose acetate membrane using polyethyleneimine for production of galactooligosaccharide
    (2010) Güleç, Hacı Ali; Gürdaş, Sevim; Albayrak, Nedim; Mutlu, Mehmet
    The aim of this study was to produce galactooligosaccharides (GOS) from lactose using ?-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 ?g/cm2 membrane) was immobilized with 66% efficiency. The Km 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°C and ? 60 h at 60°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°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 lactose. © 2010 The Korean Society for Biotechnology and Bioengineering and Springer-Verlag.
  • [ X ]
    Öğe
    Immobilization of Candida antarctica A and Thermomyces lanuginosus lipases on cotton terry cloth fibrils using polyethyleneimine
    (2012) Ondul, Eda; Dizge, Nadir; Albayrak, Nedim
    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. © 2012 Elsevier B.V..
  • Küçük Resim
    Öğe
    Lipaz aktivitesinin spektrofotometrik yöntemle belirlenmesinde çevresel koşulların p-nitrofenil propiyonat substratının kararlığına etkisi
    (Gıda Teknolojisi Derneği, 2013) Özarslaner, Eylem; Albayrak, Nedim
    Lipaz aktivitesinin spektrofotometrik yöntemle ölçülmesinde p-nitrofenol esterleri tercih edilmektedir. Yöntem, bu substratlardan lipaz hidrolizi ile açık sarı renkli p-nitrofenol (pNP) oluflturulmasına dayanmaktadır. Bu çalıflmada, lipaz aktivite ölçümünde kullanılan p-nitrofenil propiyonat (pNPP) substratının kararlılığına ve pNP ürününün ıflık soğurmasına çevresel koflulların etkisi incelenmifltir. Bekletme sıcaklığı veya süresi arttıkça, daha fazla oranda pNPP’nin kendiliğinden parçalandığı görülmüfltür. On günlük bir depolama sonunda, 4° C’ye kıyasla 20° C’de 10 katı oranında pNPP (0.512 mM) kendiliğinden parçalanmıfltır. Birbirini takip edecek flekilde 30, 60 ve 95° C’lerde sırasıyla 90, 20 ve 5 dakika inkübasyon süreleri, dakikada 0.0014, 0.0154 ve 0.0456 absorbans artıfllarına neden olmufltur. Öte yandan, oluflan pNP ürününün 400nm civarında göstereceği absorbans değeri pH 6-8 aralığında ortam pH’sına oldukça duyarlı iken; tampon kapasitesi arttıkça (0.1-1.0 M) pNP ürünün gösterdiği absorbans (404 veya 348 nm) doğrusal artarak en az 2 kat düzeyine çıkmıfltır. Bu duyarlılıklar, substratın kendiliğinden hidrolizine neden olacak koflulların azaltılması, pH ve tampon kapasitesinin standardizasyonu ile minimize edilebilmektedir. Buna ilave olarak, enzim hariç tepkime karıflımının tüm bileflenlerini içeren bir "paralel kontrol" eflliğinde denemelerin yürütülmesiyle küçük hata kaynaklarının çoğunlukla sınırlandırılabileceği tespit edilmifltir.