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    Characterization of a glucansucrase from Lactobacillus reuteri E81 and production of malto-oligosaccharides
    (Taylor & Francis Ltd, 2019) Ispirli, Humeyra; Yuzer, Mustafa Onur; Skory, Christopher; Colquhoun, Ian J.; Sagdic, Osman; Dertli, Enes
    Glucansucrases, which can be produced by different Lactic Acid Bacteria (LAB), catalyze the synthesis of alpha-glucans with different structures and properties using sucrose as substrate. In this study, a novel glucansucrase (GTFA) from Lactobacillus reuteri E81 was identified and heterologously expressed. Alignments of GTFA with other glucansucrases revealed its novelty and a putative 3D model structure was obtained. The biochemical properties of the truncated enzyme without the N-terminal variable region, GTFA-Delta N, was characterized. The K-m and V-max were found to be 7.5 mM and 1.49 IU/mg, respectively, and it showed optimum activities at pH 7 and at 50 degrees C. The GTFA-Delta N produced in vitro an alpha-glucan with (alpha 1 -> 3) and (alpha 1 -> 6) glycosidic linkages using sucrose as the substrate. Importantly, GTFA-Delta N synthesized DP = 9 oligosaccharides using sucrose and maltose as the donor and acceptor sugars, respectively, as detected by TLC, HPLC, LC-MS and NMR analysis.
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    Diversity and functional characteristics of lactic acid bacteria from traditional kefir grains
    (Wiley, 2020) Purutoglu, Kubra; Ispirli, Humeyra; Yuzer, Mustafa Onur; Serencam, Huseyin; Dertli, Enes
    Traditional kefir grains were collected from distinct parts of Turkey, and their microbial profile was determined. A wide bacterial biota was observed formed by distinct lactic acid bacteria (LAB) in which Lactococcus lactis strains appeared to be dominant. Yeast species were also identified in kefir grains. Significant levels of antifungal and antibacterial activities were monitored in kefir isolates. All tested LAB produced an exopolysaccharide (EPS) containing glucose and galactose, and some strains formed a fructan-type EPS. Importantly, low levels of antibiotic resistance were observed among the kefir isolates.
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    Effect of Heat Treatment on Storage Stability of Sheep Tail Fat
    (Sidas Medya A.S., 2024) Bozdemir Akçil, Merve; Gençcelep, Hüseyin; Yuzer, Mustafa Onur
    In this study, the effects of various physical, chemical, and technological properties of sheep tail fat (fresh and ghee) as well as different storage durations, storage temperatures, and the use of additives on the storage stability of thermally processed sheep tail fat (ghee tail fat) were investigated. To prevent lipid oxidation and other degradation factors during use after long-term storage, salt and antioxidant additives were used. Samples were stored in glass jars at 25ºC, +4ºC, and -18ºC for 90 days. The moisture, protein, fat, and ash contents of fresh tail fat was determined as 11.2%, 3.47%, 85.0%, and 0.07%, respectively. In clarified fat, the moisture content was determined as 0.4%, protein content as 2.98%, fat content as 96.0%, and ash content as 0.05%. Additionally, the cholesterol content in tail fat was 60 mg/100 g in fresh tail fat and 58 mg/100 g in ghee tail fat. The pH values of fats were determined as 5.7 in fresh samples and 6.2 in ghee samples. The fatty acid compositions of samples revealed that the dominant fatty acid groups in both fresh and ghee sheep tail fat were palmitic, stearic, and oleic acids. Fresh tail fat stored at room temperature deteriorated in terms of chemical properties (FFA, peroxide, and TBA) within 7 days, while those stored at +4ºC deteriorated within 15 days. However, thermally processed samples were preserved without deterioration for 60 days at these storage temperatures. © 2024 Sidas Medya A.S.. All rights reserved.
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    Effect of sesame protein/PVA nanofibers on oil separation and rheological properties in sesame paste
    (Wiley, 2024) Yuzer, Mustafa Onur; Genccelep, Huseyin
    This study aimed to prevent or minimize the oil phase separation that occurs during storage (0-90 days) of sesame paste at room temperature. In order to determine the changes during storage in the sesame paste samples, the zeta potential, rheological properties, and the separated oil ratio were determined. Significant (p < 0.01) effects of applied storage time and additives on the amount of oil separated in sesame pastes were determined. The oil separated in sesame paste samples varied between 3.83% and 16.29%. While the rate of separated oil increased three times in the control group over time, it showed an insignificant (p > 0.05) increase especially in the samples where 2% nanofiber was added. It was determined that the separation of the oil phase from the structure could be prevented up to 24.73% with the addition of SPI and up to 63.02% with addition of SPINL (nanofiber containing protein isolate) compared to the control.Practical applicationsDuring storage, the particles in the sesame paste tend to precipitate, causing oil separation and residue cake, thus negatively affecting the acceptability of consumers. Additives were added in order to prevent or minimize oil phase separation, which occurs in sesame paste stored at room temperature and is not desired by consumers. As additives, nanofibers containing sesame proteins produced by the electrospinning method and sesame protein isolates (SPIs) were added. Added additives acted by preventing the separation of the oil phase from the structure. It has been determined that the addition of SPI to sesame pastes does not completely prevent the problem of oil separation in sesame paste, but is effective in delaying and reducing it. Since the oil decomposition can be reduced, the amount of oil separated and therefore the part that can sink to the bottom will decrease, so sesame paste will be consumed more appropriately and will contribute to the country's economy.
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    Optimization of Hemp Seed (Cannabis sativa L.) Protein Extraction and Glycation Conditions by Response Surface Methodology: Physicochemical, Functional, and Thermal Characteristics
    (Wiley, 2025) Yuzer, Elvan; Kutlu, Naciye; Yuzer, Mustafa Onur
    In this study, first, optimization using the response surface method was implemented to obtain the highest yield of protein isolate from defatted hemp seed under different extraction conditions. Optimum extraction conditions were determined with 0% salt concentration, 12 pH value, and 49 degrees C temperature. The protein isolate produced under optimum conditions was subjected to the glycation process, and the glycation conditions were also optimized. The optimum conditions for glycation were determined as a protein isolate: sugar ratio of 1.6:1, temperature of 60 degrees C, and time of 90 min, providing the most suitable glycation degrees and browning indices. There was no statistical difference between the glycated protein isolate obtained under these conditions and the nonglycated protein isolate in terms of emulsifying activity index and emulsion stability index. For total phenolic-flavonoid compounds and antioxidant activity, the sugar complex caused a decrease in these values. In addition, there was a high positive correlation between bioactive compounds. SEM micrographs showed relationships between hemp seed protein isolate and sugar, and these interactions led to a spongy three-dimensional microstructure. When the FTIR results were analyzed, the glycated isolate had stronger absorption at 3300-3200 cm-1 compared to the nonglycated isolate. In conclusion, this study reports important findings in terms of functional and characteristic properties of how monosaccharides affect glycation.