Person: TOKSOY ÖNER, EBRU
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TOKSOY ÖNER
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Publication Metadata only Rheological characteristics of exopolysaccharides (EPSs) produced by Brevibacillus thermoruber(ELSEVIER SCIENCE BV, 2012) TOKSOY ÖNER, EBRU; Yildiz, Songul Yasar; Ozer, Tugba; Radchenkova, Nadia; Genc, Seval; Oner, Ebru Toksoy; Kambourova, MargaritaPublication Open Access Evaluation of the Potential Use of Levan Polysaccharide in Paper Conservation(WILEY-HINDAWI, 2020-08-10) TOKSOY ÖNER, EBRU; Saglam, Rumeysa Ozen; Genc, Seval; Oner, Ebru ToksoyConservation of paper-based materials, namely, manuscripts, includes repair of tears, gap filling, consolidation, and fixation, which requires the use of adhesives. The adhesive in use for these purposes should be compatible with the chemical and physical properties of paper and should present good aging characteristics. In this study, we conducted a set of experiments with paper samples on which fructan-based biopolymer Halomonas levan (Hlevan) was applied for the first time and compared with glucan-based adhesive starch. Adhesive-applied samples were initially prepared by the application of different historical recipes of sizing and ink. Then, they underwent accelerated thermal aging. Chemical and physical changes of paper samples (crystallinity, pH, and color) were analyzed. Finally, Principal Component Analysis was performed to identify dominating factors affecting sample behavior with applied adhesives. This study demonstrates the aging characteristics of Hlevan on cellulose-based materials. The results showed that there is a color shift from blue to yellow for all samples after aging, but it is more pronounced for some samples with Hlevan. In addition, Hlevan is slightly less acidic than starch in all cases and acted as a plasticizer for a specific kind of sizing material. The methodology of this research is also efficacious in terms of understanding the interaction of paper media with the adhesives and their effects on aging.Publication Open Access Synthesis and characterization of interpenetrating network (IPN) based levan-polyacrylamide hydrogels and their application in conservation of cultural heritage(2023-11-01) ÜNAL YILDIRIM, SEMRA; OKTAR, FAİK NÜZHET; GENÇ, SEVAL; TOKSOY ÖNER, EBRU; Özen Sağlam R., Ünal Yıldırım S., Oktar F. N., Genç S., Erdem G., Toksoy Öner E.In this study, an IPN based enzymatic levan-polyacrylamide hydrogel (EL-PA) was developed and characterized for its structural, morphological, rheological properties and swelling kinetics to underline hydrogel properties and its potential use in paper conservation. The addition of levan also led to changes in the viscoelastic behavior of the hydrogels, with the complex viscosity of EL-PA samples showing pronounced dependence on shear rate. The swelling and the overall surface area of the hydrogels were increased with the addition of levan into the polymer network. Source associated structural differences were found to be negligible such that both microbially produced linear and enzymatically produced branched forms of levan performed equally well. Solvent loaded hydrogels were then applied on an artifact, a 19th century book of Namık Kemal, and investigated using FTIR, SEM, XRD and colorimetric analysis. Old adhesive layers were successfully removed, and hydrogels showed good compatibility and ease of application. This study has shown that levan has improved hydrogel properties and levan based systems bear high potential in conservation science.Publication Metadata only Synthesis and characterization of levan hydrogels and their use for resveratrol release(SAGE PUBLICATIONS LTD, 2021) TOKSOY ÖNER, EBRU; Selvi, Sinem Selvin; Haskoylu, Merve Erginer; Genc, Seval; Toksoy Oner, EbruConsidering the need for systematic studies on levan based hydrogels to widen their use in drug delivery systems and biomedical applications, this study is mainly focused on the synthesis and comprehensive characterization as well as drug release properties of hydrogels based on Halomonas levan (HL) and its chemical derivatives. For this, hydrolyzed and phosphonated HL derivatives were chemically synthesized and then cross-linked with 1,4-Butanediol diglycidyl ether (BDDE) and the obtained hydrogels were characterized in terms of their swelling, adhesivity, and rheological properties. Both native and phosphonated HL hydrogels retained their rigid gel like structure with increasing shear stress levels and tack test analysis showed superior adhesive properties of the phosphonated HL hydrogels. Moreover, hydrogels were loaded with resveratrol and entrapment and release studies as well as cell culture studies with human keratinocytes were performed. Biocompatible and adhesive features of the hydrogels confirmed their suitability for tissue engineering and drug delivery applications.Publication Metadata only Halomonas smyrnensis as a cell factory for co-production of PHB and levan(ELSEVIER SCIENCE BV, 2018) KASAVİ, CEYDA; Tohme, Souha; Haciosmanoglu, Gul Gulenay; Eroglu, Mehmet Sayip; Kasavi, Ceyda; Genc, Seval; Can, Zehra Semra; Oner, Ebru ToksoyLevan is a fructan type polysaccharide that has long been considered as an industrially important biopolymer however its limited availability is mainly due to the bottlenecks associated with its large-scale production. To overcome such bottlenecks in the commercialization of this very promising polysaccharide, co-production of levan with polyhydroxyalkanoates (PHAs) by halophilic Halomonas smyrnensis cultures has been proposed in this study for the first time. After in silico and in vitro assessment of PHA accumulation, fermentation profiles for levan and PHA concentrations were obtained in the presence of sucrose and glucose and the PHA granules observed by TEM were found to be poly(3-hydroxybutyrate) (PHB) after detailed structural characterization by GC-MS, DSC, FTIR and NMR. Six nutrient limitation strategies based on nitrogen (N) and phosphorus (P) were tested but highest levan and PHB yields were obtained under unlimited conditions. H. smyrnensis is proved to co-produce PHB and levan while using inexpensive carbon sources which is a commercially successful microbial cell factory system showing a great potential in lowering manufacturing costs and aiming for a zero waste policy within the biorefinery concept. (C) 2018 Elsevier B.V. All rights reserved.