Halbay Turumtay
Karadeniz Technical University, Energy System Engineering, Faculty Member
Huge energy demand with increasing population is addressing renewable and sustainable energy sources. A solution to energy demand problem is to replace our current fossil fuel-based economy with alternative strategies that do not emit... more
Huge energy demand with increasing population is addressing renewable and sustainable energy sources. A solution to energy demand problem is to replace our current fossil fuel-based economy with alternative strategies that do not emit carbon dioxide. Plant biomass is one of the best candidates for this issue. Plants use solar power to convert carbon dioxide and water into sugars, which can be used in fermentation reactions to produce both energy and materials. However, the desired sugars are trapped in the highly recalcitrant cell wall as building blocks of cellulose chains. Moreover, the complexity of the plant cell wall structure hinders the hydrolysis of cellulose into fermentable sugar monomers. Although pretreatments are used to change the physical and chemical properties of the lignocellulosic biomass and improve hydrolysis rates, these pretreatments often use harsh and polluting chemicals and severely increase the cost of biofuel production. The goal of the review is to summarize recent researches, which describe generating plants with a modified cell wall and improve hydrolysis of cellulose without applying any or less pretreatment methods. Since pretreatment of lignocellulosic biomass is the most cost effective step in biofuel production, generating autodigestible plants could reduce the production cost of biofuels and bio-based biomaterials. One of the strategies to improve biomass conversion efficiency is the modification of the cell wall by heterologous expression of cell wall-modifying proteins. These cell wall-modifying proteins could alter the cell wall structure and reduce cell wall recalcitrance. The use of such transgenic technologies would consume less energy and chemicals when cellulose is more accessible for enzymatic hydrolysis.
Research Interests:
To study the effect of short N-acetylglucosamine (GlcNAc) oligosaccharides on the physiology of plants, N-ACETYLGLUCOSAMINYLTRANSFERASE (NodC) of Azorhizobium caulinodans was expressed in Arabidopsis (Arabidopsis thaliana). The... more
To study the effect of short N-acetylglucosamine (GlcNAc) oligosaccharides on the physiology of plants, N-ACETYLGLUCOSAMINYLTRANSFERASE (NodC) of Azorhizobium caulinodans was expressed in Arabidopsis (Arabidopsis thaliana). The corresponding enzyme catalyzes the polymerization of GlcNAc and, accordingly, beta-1,4-GlcNAc oligomers accumulated in the plant. A phenotype characterized by difficulties in developing an inflorescence stem was visible when plants were grown for several weeks under short-day conditions before transfer to long-day conditions. In addition, a positive correlation between the oligomer concentration and the penetrance of the phenotype was demonstrated. Although NodC overexpression lines produced less cell wall compared with wildtype plants under nonpermissive conditions, no indications were found for changes in the amount of the major cell wall polymers. The effect on the cell wall was reflected at the transcriptome level. In addition to genes encoding cell wall-modifying enzymes, a whole set of genes encoding membrane- coupled receptor-like kinases were differentially expressed upon GlcNAc accumulation, many of which encoded proteins with an extracellular Domain of Unknown Function26. Although stress-related genes were also differentially expressed, the observed response differed from that of a classical chitin response. This is in line with the fact that the produced chitin oligomers were too small to activate the chitin receptor-mediated signal cascade. Based on our observations, we propose a model in which the oligosaccharides modify the architecture of the cell wall by acting as competitors in carbohydrate-carbohydrate or carbohydrate-protein interactions, thereby affecting noncovalent interactions in the cell wall or at the interface between the cell wall and the plasma membrane.
Research Interests:
Phenolic compounds of Thymus praecox Opiz subsp. caucasicus var. caucasicus were analyzed by high performance liquid chromatography equipped with an ultraviolet detector (HPLC-UV). Quercetin (co-eluting with luteolin) and caffeic acid... more
Phenolic compounds of Thymus praecox Opiz subsp. caucasicus var. caucasicus were analyzed by high performance liquid chromatography equipped with an ultraviolet detector (HPLC-UV). Quercetin (co-eluting with luteolin) and caffeic acid were among the most abundant compounds identified. In addition syringic, ferulic, p-coumaric, protocatechuic,p-hydroxybenzoic and vanillic acid as well as the flavonoids catechin, epicatechin, and kaempferol were identified and quantified in the plant extracts. Acidic hydrolysis was used to gain additional information on the glycosylation state of the phenolics. Although chromatographic profiles changed considerable upon hydrolysis, quercetin and caffeic acid remained among the most abundant compounds identified. In addition the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activities of different tissues were determined and correlations were found between phenolic or flavonoid content and antioxidant property with strongest radical scavenging activity in hydrolyzed flower extracts.
Research Interests:
Tea with different parts (flower, leaf, seed) of Sideritis condensate infused at different temperatures (60 and 100°C) and times (5, 10 and 30 minutes) were assessed for their phenolic composition and antioxidant activities. Leaf tea had... more
Tea with different parts (flower, leaf, seed) of Sideritis condensate infused at different temperatures (60 and 100°C) and times (5, 10 and 30 minutes) were assessed for their phenolic composition and antioxidant activities. Leaf tea had the highest total phenolic content where as seed tea had the lowest.Leaves soaked at 100°C for 10 minutes had the highest total phenolic content. Total phenolic content of flower tea increased with increase in extraction temperature and time. Radical scavenging activities of leaves infused at 60°C for 5, 10 and 30 minutes were statistically in the same group but lower than those of leaves soaked at 100°C for 5, 10 and 30 min. The major phenolic compound identified from almost all aqueous infusions was the p-coumaric acid. The conditions of tea prepared from leaves of the Sideritis condensata at 100°C for 5, 10 and 30 minutes are the most appropriate conditions in regard to extraction of the highest total phenolics and the strongest antioxidant activity.