Browsing by Author "Gul O."

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A novel spectrophotometric method based on Seliwanoff test to determine 5-(Hydroxymethyl) furfural (HMF) in honey: Development, in house validation and application
(2021-03-01) Besir A.; Yazici F.; Mortas M.; Gul O.
A new spectrophotometric method for the determination of 5-(Hydroxymethyl) furfural (5-HMF) in honey was proposed. In the proposed method based on the qualitative Seliwanoff test, quantitative determination was carried out by measuring the red color formed by reacting the HMF and Seliwanoff reagent (resorcinol-HCl). Central Composite Design (CCD) was used to obtain optimum reaction parameters. The limit of detection, LOD (2.69 mg kg−1) and limit of quantification, LOQ (8.97 mg kg−1) were established in the model honey matrix. Precision (as RSD for inter and intraday precision) was in the range of 2.52–5.14%. Accuracy results obtained exhibit a good recovery (from 95.83% to 96.65%). Good selectivity and linearity (R2 > 0.99) were also observed. HMF amounts in honey samples determined by the proposed method were found to be in a relatively good agreement with those obtained by the spectrophotometric Winkler method (r = 0.9880) and HPLC-UV method (r = 0.9888).
Development and characterization of black mulberry (Morus nigra) pekmez (molasses) composite films based on alginate and pectin
(2020-10-01) Cakıroglu K.; Dervisoglu M.; Gul O.
Production of composite films is an important approach to improve functionality of edible films, by combining different polysaccharides, proteins, and lipids. Carbohydrate-based composite films are most attractive, which have good film-forming ability due to their unique colloidal properties. Fruit purees include high polysaccharide content that plays a role to have desirable film properties including mechanical resistance, efficient barrier properties, and selective permeability against oxygen transmission. The purpose of this study was to characterize physical, barrier, mechanical, thermal, and water sorption properties of composite films formulated with different mulberry pekmez concentrations (26, 32, and 38 °Brix) based on alginate or pectin. All film-forming solutions were showed shear thinning behavior with higher yield stress and viscosity-shear rate data were fitted to Ostwald de Waele model (R2 ≥ 0.943). A noticeable decrease in tensile strength of films with increasing concentration was determined, but films prepared with high concentration showed more flexible. The mechanical properties of pectin films exhibited weakened properties compared to alginate films. Increasing pekmez concentration in the film matrix improved the water vapor permeability of alginate films, whereas pectin films showed reverse behavior as resulting in cracks and crack propagation within the structure. The sorption isotherms of films showed a typical profile of foods contain high soluble components and the Guggenheim–Anderson–deBoer (GAB) model gave a good fit for all of the obtained data. The results showed that mulberry pekmez films based alginate have a potential for food applications depends on the physical properties and for the replacement of non-biodegradable plastic packaging.
Effect of high pressure homogenization on microstructure and rheological properties of hazelnut beverage cold-set gels induced glucono-δ-lactone
(2021-05-01) Gul O.; Saricaoglu F.T.; Atalar I.
In this study, high pressure homogenized (HPH) hazelnut beverage samples were acidified with glucono-δ-lactone (GDL) and rheological, structural and gel strength properties of the cold-set gels were characterized. Hazelnut beverage at a concentration of 10 g 100 mL−1 was treated with HPH up to 150 MPa pressure and then mixed with GDL (2 g 100 mL−1). Gelation of hazelnut beverages was observed with small deformation oscillatory measurements during 150 min. Hazelnut beverages acidified with GDL displayed shear thinning behavior due to decreasing viscosity with increasing shear rate, however, HPH led to an increase in apparent viscosities of cold set hazelnut beverage gels. Cold set hazelnut beverages were characterized as weak gel-like macromolecular dispersions due to storage modulus (G′) was higher than loss modulus (G″). Angular frequency dependence of complex modulus (G*) was studied to measure the strength of the cross-linking protein network of suspension systems by calculating a constant order of relaxation function (α) and concentration-dependent stiffness parameter (Aα). This study revealed for the first time that hazelnut proteins can form good gel structures with acidification, and gel properties can be improved by HPH treatment.
Effect of sesame protein isolate modified by high-pressure homogenization, high-intensity ultrasound, and high-pressure processing on the colloidal stability of sesame paste: Determination of physicochemical, rheological, microstructural properties and storage stability
(2024-08-01) Gul O.; Sahin M.S.; Saricaoglu F.T.; Atalar I.
Effect of ultrasonication treatment on structural, physicochemical and bioactive properties of pasteurized rosehip (Rosa canina L.) nectar
(2020-01-01) Atalar I.; Saricaoglu F.T.; Odabas H.I.; Yilmaz V.A.; Gul O.
The effect of ultrasonication process (US) on the physical and bioactive properties of pasteurized rosehip nectar was investigated. In order to solve sedimentation problem, two amplitude levels (50 and 100%) and different treatment times (5, 10, 15 and 30 min) were applied to rosehip nectars. Mean particle size decreased as amplitude and treatment time increased. US treatment caused to increase in redness and yellowness values of nectars and also color change was found noticeable as 1.9–2.6 at 100% amplitudes. US treated samples showed no sedimentation during storage for 15 days while control sample displayed 74% colloidal stability. All samples showed shear-thinning behavior and were characterized as weak gel network. Total phenolic and carotenoid contents and antioxidant activity was increased by US treatment, however, ascorbic acid content decreased. US treatment can be an alternative technology preventing sedimentation problems during shelf life with minimally affecting bioactive and physical properties of rosehip nectar.
Improved physicochemical, rheological and bioactive properties of ice cream: Enrichment with high pressure homogenized hazelnut milk
(2021-07-01) Atalar I.; Kurt A.; Gul O.; Yazici F.
High pressure homogenized hazelnut milk (HM) as a functional food compound was incorporated into ice cream as a replacer of cow milk (0-25-50-75-100%) to investigate its effect on the rheological, textural, physical, functional, and sensory properties of ice cream. Rheological experiments showed that the water-holding properties, flow behaviors, and emulsifying capacity of ice creams were improved by increasing HM ratio (p < 005) due to the more developed structure and a higher degree of molecular connectivity. At higher HM concentrations, the reduced melting rates and retarded first dripping time values were observed (p < 005) for ice creams, exhibiting higher consistency, material stiffness values, total phenolic content and antioxidant activity. The usage of HM up to 75% concentrations in ice cream production improved the acceptability of the product enhancing their sensory parameters. The enrichment of ice cream with HM may help to enhance the functional, structural, and also nutritional characteristics of dairy products.
Influence of pH and ionic strength on the bulk and interfacial rheology and technofunctional properties of hazelnut meal protein isolate
(2023-07-01) Gul O.; Gul L.B.; Baskıncı T.; Parlak M.E.; Saricaoglu F.T.
The functional, bulk, and interfacial shear rheological properties of hazelnut protein isolate were studied at different pH values between 3.0 and 8.0 and ionic strength levels between 0.0 and 1.0 M. The results showed that pH significantly affected protein solubility, emulsion properties, water and oil holding capacities, foam stability, surface hydrophobicity, and free -SH groups. The highest surface hydrophobicity, free -SH groups, and better functional properties were observed at pH 8.0. Protein solubility also increased with increasing ionic strength up to 0.6 M. The emulsion and foam stability of hazelnut protein isolate showed similar changes with protein solubility. The flow behavior of hazelnut protein suspensions was found to be shear thinning with the highest consistency index at pH 3.0 and the lowest at pH 6.0, however, the ionic strength did not significantly affect the consistency coefficient but did cause a significant change in the flow behavior index, with the lowest value observed at 0.6 M. The best gel structure in hazelnut proteins was observed at pH 3.0 and 4.0. The addition of ions at 0.4 and 0.6 M concentrations resulted in an improved viscoelastic character. The hazelnut protein isolate was also found to form solid-like viscoelastic layers at both air-water and oil-water interfaces, with the interfacial adsorption behavior affected by both pH and ionic strength. Overall, these results suggest that pH and ionic strength have significant effects on the functional and rheological properties of hazelnut protein isolate, which may have the potential as an auxiliary substance in food systems.
Modifications to structural, techno-functional and rheological properties of sesame protein isolate by high pressure homogenization
(2023-10-01) Baskıncı T.; Gul O.
Optimization of cryoprotectant formulation to enhance the viability of Lactobacillus brevis ED25: Determination of storage stability and acidification kinetics in sourdough
(2020-04-01) Gul L.B.; Gul O.; Yilmaz M.T.; Dertli E.; Con A.H.
In this study, various kinds of cryoprotectant (skim milk, lactose, and sucrose) formulations were tested to enhance the survival of Lactobacillus brevis ED25 after freezing and freeze-drying. A Box–Behnken experimental design was used to optimize cryoprotective medium and the highest cell survival was observed with the 17.28% skim milk, 2.12% lactose, and 10% sucrose cryoprotectant as the optimum condition. The structural and physicochemical characteristics of freeze-dried powder were acceptable for application with regards to particle surface morphology, moisture and water activity (Aw), glass transition temperature (Tg), Fourier transform infrared spectra, X-ray structure, and also storage stability under the refrigeration and room temperature conditions. Accelerated storage test based on Arrhenius equation could be used to predict the freeze-dried bacterial shelf life but only with a certain degree of predictability for long-term storage. The acidification kinetics of fresh and stored culture in sourdough fermentation was also described on the basis of the Gompertz equation. Practical applications: Freezing and storage are crucial factors for the viability and acidification power of starter culture. Therefore, various types and concentrations of cryoprotectants have been used to preserve the microorganisms. L. brevis ED25 has been a good potential for the manufacture of industrial sourdoughs and this research has aimed to investigate long-term protective effects of optimum cryoprotectant formulations on the viability of bacteria and also determine the acidification power in sourdough. The results showed the potential value of freeze-dried L. brevis ED25 culture for commercialization.
Optimization of fermentation conditions for sourdough by three different lactic acid bacteria using response surface methodology
(2022-01-12) Gul L.B.; Gul O.; Con A.H.
This study aimed to investigate optimal fermentation conditions for sourdough by freeze-dried Lactobacillus curvatus N19, Weissella cibaria N9 and Lactobacillus brevis ED25 isolated from Turkish sourdough previously. The central composite rotational design was applied to the optimization of fermentation parameters (temperature and time). The fermentation was carried out under a simulated sourdough system and biomass concentration, total acidity, and lactic and acetic acid formation were chosen as response variables. Results showed that the models developed for all variables were significant (p < 0.05) and there was no lack of fit in any of quantifications (p > 0.05), indicating the suitability for representing the relationship between variables and factors. While both of the independent parameters were effect the response, fermentation time was the most significant factor influencing the response. The validation experiments using the optimized condition showed a good agreement between the experimental and predicted values except the lactic and acetic acid formation for W. cibaria N9. In conclusion, freeze-dried L. curvatus N19 can be used as a starter culture to sourdough fermentation for bread industry due to optimum fermentation conditions (29oC temperature and 23h time).
Potential Use of High Pressure Homogenized Hazelnut Beverage for a Functional Yoghurt-Like Product
(2022-01-01) Gul O.; Atalar I.; Mortas M.; Saricaoglu F.T.; Besir A.; Gul L.B.; Yazici F.
Hazelnut beverage is a plant-based beverage produced from hazelnut cake as a by-product obtained after cold press extraction. It has high nutritional value and a significant percentage of consumers show interest in it due to its health benefits. In this study, hazelnut beverage manufactured from by-products of hazelnut oil industry was incorporated into functional yoghurt production. Five formulations (ratio of 1/0, 3/1, 2/1, 1/1, 0/1, v/v, cow milk/hazelnut beverage) of yoghurt-like products were prepared to indicate the storage period of the samples and the analysis performed. For yoghurt production, hazelnut beverage and cows' milk were standardized to 14.5 g 100 g -1 with skimmed milk powder. The use of hazelnut beverage in yoghurt production negatively affected L. bulgaricus counts. Water holding capacity and viscosity values were improved by using hazelnut beverage. Increasing hazelnut beverage concentration led to an increase in the total phenolic compounds and antioxidant activity, malic acid levels and also unsaturated fatty acids, especially oleic and linoleic acid. Using the ratio of 3/1 was found the best in view of appearance, flavor and overall acceptability. Based on the structural, rheological and sensorial properties, this study could guide the dairy industry to use hazelnut beverage obtained from hazelnut cake.
Storage stability and sourdough acidification kinetic of freeze-dried Lactobacillus curvatus N19 under optimized cryoprotectant formulation
(2020-10-01) Gul L.B.; Con A.H.; Gul O.
In this study, the response surface methodology was used to optimize the cryoprotective agent (skimmed milk powder, lactose and sucrose) formulation for enhancing the viability of Lactobacillus curvatus N19 during freeze-drying and storage stability of cells freeze-dried by using optimum formulation was evaluated. Our results showed that the most significant cryoprotective agent influencing the viability of L. curvatus N19 to freezing and freeze-drying was sucrose and skim milk, respectively. The optimal formulation of cryoprotective agents was 20 g/100 mL skim milk, 3.57 g/100 mL lactose and 10 g/100 mL sucrose. Using the optimum formulation during freeze-drying, the cell survival was found more than 98%. Under the optimal conditions, although only storage of the cells at 4 °C for 6 month retained the maximum stability (8.85 log cfu/g), the employed protectant matrix showed promising results at 25 °C (7.89 log cfu/g). The storage stability of cells under optimized conditions was predicted by accelerated storage test, which was demonstrated that the inactivation rate constant of the freeze-dried L. curvatus N19 powder was 9.74 × 10−6 1/d for 4 °C and 2.08 × 10−3 1/d for 25 °C. The loss of specific acidification activity after the storage at 4 and 25 °C was determined.
Structural Characterization, Technofunctional and Rheological Properties of Sesame Proteins Treated by High-Intensity Ultrasound
(2023-05-01) Gul O.; Saricaoglu F.T.; Atalar I.; Gul L.B.; Tornuk F.; Simsek S.
Plant-derived proteins, such as those from sesame seeds, have the potential to be used as versatile food ingredients. End-use functionality can be further improved by high-intensity ultrasound treatments. The effects of high-intensity ultrasound on the properties of sesame protein isolates from cold-pressed sesame cake were evaluated. The SDS-PAGE demonstrated no significant changes in the molecular weight of proteins. Ultrasound treatments resulted in decreased particle size with a more uniform distribution, resulting in the exposure of hydrophobicity and free −SH groups and increased zeta potential. Although FTIR spectra of proteins were similar after ultrasonication, a partial increase in the intensity of the amide A band was observed. The ultrasound significantly (p < 0.05) affected the secondary structure of proteins. While optical micrographics revealed a dispersed structure with smaller particles after treatments, microstructural observations indicated more rough and irregular surfaces. Water solubility was improved to 80.73% in the sample subjected to 6 min of ultrasonication. Sesame protein solutions treated for 4 and 6 min exhibited viscoelastic structure (storage modulus (G′) > loss modulus (G′′)). In addition, the gelation temperature of proteins decreased to about 60–65 °C with increasing treatment time. Overall, ultrasound is a useful technique for the modification of sesame protein isolates.