Sibel Tunç

A method for the measurement of the oxygen permeability and the development of edible films to reduce the rate of oxidative reactions in fresh foods

Abstract A method involving the flow of O 2 and N 2 gasses from the two sides of an edible film coupled with a simple wet chemical analysis at the end, was developed to measure the oxygen permeability of edible films. The proposed method was employed to determine the oxygen permeability of methyl cellulose (MC)-based edible films of various composition with the aim of finding the optimum composition for minimising oxidative degradation of foods. The effects of the presence of stearic acid (SA), ascorbic acid (AA) and citric acid (CA), in varying amounts in the film composition, on the oxygen permeability (OP) of MC based edible films were examined. The OP increased with increasing SA content of the film and decreased with the inclusion of AA or CA in the film composition. The films, with various compositions and with the measured oxygen permeabilities, were then applied to mushrooms ( Agaricus bisporus ) and cauliflower ( Brassica botrytis ). It was found, from the analysis of these coated foods, that the coatings containing antioxidants slowed the browning reactions and reduced the vitamin C loss in both foods, the effects being greater in cauliflower. Moreover, the moisture loss of coated foods was less than that of uncoated.

Synthesis of magnetic oxidized multiwalled carbon nanotube-κ-carrageenan-Fe3O4 nanocomposite adsorbent and its application in cationic Methylene Blue dye adsorption

In this study, magnetic oxidized multiwalled carbon nanotube (OMWCNT)-Fe3O4 and OMWCNT-κ-carrageenan-Fe3O4 nanocomposites were synthesized and used as adsorbent for the removal of Methylene Blue (MB) from aqueous solution. Magnetic nanocomposites were characterized by using of specific surface area, Fourier transform infrared, X-ray diffraction, vibrating sample magnetometry, thermal gravimetric analysis, scanning electron microscope and transmission electron microscope measurements. The results of characterization analyses exhibited that OMWCNT was successfully modified with κ-carrageenan. Furthermore, OMWCNT-Fe3O4 and OMWCNT-κ-carrageenan-Fe3O4 nanocomposites were of a super-paramagnetic property. Adsorption studies revealed that the data of adsorption kinetics and isotherm were well fitted by the pseudo second-order kinetic model and Langmuir isotherm model, respectively. The adsorption amounts of magnetic adsorbents increased with contact time and initial dye concentration. Compared with magnetic OMWCNT-Fe3O4 nanocomposite, magnetic OMWCNT-κ-carrageenan-Fe3O4 nanocomposite showed a better adsorption performance for the removal of MB from aqueous solution. Therefore, OMWCNT-κ-carrageenan-Fe3O4 nanocomposite may be used as a magnetic adsorbent to remove the cationic dyes from wastewaters.

The effect of fatty acid content on water vapour and carbon dioxide transmissions of cellulose-based edible films

Abstract Water vapour and CO 2 transmissions of methyl cellulose (MC)-based edible films with varying amounts of the fatty acids, stearic acid (SA), palmitic acid (PA) and lauric acid (LA) were studied and the results were compared with those obtained for a film without added fatty acid. Water vapour transmission rate (WVTR), water vapour permeance (WVPN) and water vapour permeability (WVP) values of films were determined by measuring the amounts of water vapour transmitted through the film and then adsorbed on anhydrous CaCl 2 as a function of time, using a static method. A recently-developed static method which utilises ascarite to adsorb carbon dioxide transmitted through the film was employed for the determination of carbon dioxide transmission rate (CO 2 TR), carbon dioxide permeance (CO 2 PN) and carbon dioxide permeability (CO 2 P) of films. Among the three fatty acids studied, SA was found to be the most effective in decreasing both the water vapour and the CO 2 transmissions of films. In general, it was observed that WVTR, WVPN and WVP values of films decreased with increasing fatty acid content in the film composition. CO 2 transmission parameters also decreased with increasing SA and PA contents but increased with increasing LA content of films.

Spectroscopic investigations of the interactions of tramadol hydrochloride and 5-azacytidine drugs with human serum albumin and human hemoglobin proteins.

The interactions of tramadol hydrochloride (THC) and 5-azacytidine (AZA) drugs with human serum albumin (HSA) and human hemoglobin (HMG) proteins were investigated by fluorescence, UV absorption and circular dichroism (CD) spectroscopy at pH 7.4 and different temperatures. The UV absorption spectra and the fluorescence quenching of HSA and HMG proteins indicated the formation of HSA-THC and HMG-THC complexes via static quenching mechanism. AZA did not interact with HSA and HMG proteins. It was found that the formation of HMG-THC complex was stronger than that of HSA-THC complex. The stability of HSA-THC and HMG-THC complexes decreased with increasing temperature. The number of binding site was found as one for HSA-THC and HMG-THC systems. Negative enthalpy change (ΔH) and Gibbs free energy change (ΔG) and positive entropy change (ΔS) values were obtained for these systems. The binding of THC-HSA and HMG proteins was spontaneous and exothermic. In addition, electrostatic interactions between protein and drug molecules played an important role in the binding processes. The results of CD analysis revealed that the addition of THC led to a significant conformational change in the secondary structure of HSA protein, on the contrary to HMG protein.

Study on the bindings of dichlorprop and diquat dibromide herbicides to human serum albumin by spectroscopic methods

The interactions of dichlorprop (DCP) and diquat dibromide (DQ) herbicides with human serum albumin (HSA) protein were studied by UV absorption, fluorescence, synchronous fluorescence and circular dichroism (CD) spectroscopy. Both DCP and DQ quenched the fluorescence emission spectrum of HSA through the static quenching mechanism. The Stern-Volmer quenching constant, binding constant, the number of binding sites and thermodynamic parameters were determined at 288K, 298K, 310K and 318K. In HSA-DCP and HSA-DQ systems, an increase in temperature led to a decrease in the Stern-Volmer quenching constant and binding constant. One binding site was obtained for DCP and DQ on HSA. It was found that DCP can bind to HSA with higher affinity than DQ. Negative ΔH and positive ΔS values were obtained for the binding processes between protein and herbicide molecules. This result displayed that electrostatic interactions play a major role in the formation of HSA-DCP and HSA-DQ complexes. The binding processes were exothermic reactions and spontaneous. In addition, synchronous fluorescence and CD spectra of HSA revealed that the binding of DCP to HSA did not cause a significant conformational change in protein, but the interaction of DQ with HSA led to an alteration in the protein structure.

Electrokinetic Properties of Vermiculite and Expanded Vermiculite: Effects of pH, Clay Concentration and Mono- and Multivalent Electrolytes

Abstract In this study, the zeta potential values of vermiculite and expanded vermiculite were measured to determine the effect of pH, clay concentration, and various mono- and multivalent electrolytes including NaCl, KCl, NH4Cl, NaNO3, NaClO4, Na2SO4, Na2CO3, Na3PO4·12H2O, MgCl2·6H2O, CaCl2·2H2O, BaCl2, SrCl2·6H2O, CuCl2·2H2O, CoCl2·6H2O, NiCl2, AlCl3, and CrCl3·6H2O on the electrokinetic properties of vermiculite samples. It was found that generally the measured zeta potential values of expanded vermiculite for the studied systems were slightly more negative than that of vermiculite. The pH profiles of vermiculite and expanded vermiculite at acidic, natural, and basic pH values were obtained to determine the effect of time on the pH values of clay suspensions. The zeta potential measurements showed that the surface charge of clay particles was negative in water. The isoelectric point of vermiculite and expanded vermiculite were determined as pH 2.30 and 2.57, respectively. Divalent cations (Mg2+, Ca2+, Sr2+, and Ba2+), heavy metal ions (Cu2+, Ni2+, and Co2+) and trivalent cations (Al3+ and Cr3+) were potential determining ions for vermiculite and expanded vermiculite particles. Moreover, divalent and trivalent cations caused the change of surface charge from negative to positive. On the other hand, monovalent cations (Na+, K+ and NH4 +), monovalent anions (Cl−, NO3 −, and ClO4 −) and multivalent anions (SO4 2−, CO3 2−, and PO4 3−) acted as indifferent ions for these clay particles.

Effects of montmorillonite on properties of methyl cellulose/carvacrol based active antimicrobial nanocomposites.

The effect of montmorillonite and carvacrol (as an antimicrobial agent) on the wettability, mechanical, gas barrier, thermal and color properties of methyl cellulose-based nanocomposite films was investigated. To make a comparison among the film samples, methyl cellulose (MC) film and methyl cellulose/montmorillonite (MC/MMT) and methyl cellulose/carvacrol/montmorillonite (MC/CRV/MMT) nanocomposite films with different clay concentration were prepared. The interactions among MMT, CRV and film matrix were characterized by FTIR spectroscopy. The contact angle value of MC film showed an increase of 2.5 fold with the incorporation of 60wt.% MMT into the film matrix. The addition of clay into the film matrix increased the melting point of MC film and improved the mechanical properties of film material. The tensile stress of pure MC film exhibited an increase of 9.2MPa in the presence of 60wt.% MMT. With the addition of MMT into the film matrixes, water vapor permeability values of MC film and MC/CRV film were decreased by 28% and 13%, respectively. The incorporation of 60wt.% MMT into the film matrix caused to a decrease of 47 fold for MC film and 16 fold for MC/CRV film in the oxygen permeability of film sample. The addition of CRV into MC film and MC/MMT nanocomposite films with different clay concentration reduced the mechanical strengths of film materials. Oxygen permeability values of MC film and MC/MMT nanocomposite films decreased with the inclusion of CRV into the film matrix.

Effects of Electrolytes on the Electrokinetic Properties of Pumice Suspensions

Zeta potential values of particles and their sign are very important in many applications. In this study, the zeta potential values of pumice were obtained in the presence of various monovalent (LiCl, NaCl, KCl, NaClO4, and NaNO3), divalent (MgCl2, CaCl2, SrCl2, BaCl2, CuCl2, MnCl2, NiCl2, Na2CO3, and Na2SO4) and trivalent (AlCl3 and Na3PO4) salts. The zeta potential measurements were performed as a function of pumice concentration, pH, ionic species and electrolyte concentration by electrophoresis technique. The pH profiles of pumice/water systems at different pH values were obtained to determine the stability of suspension pH. The results showed that the zeta potential values of pumice in water did not change significantly with pumice concentration, while they changed mostly with pH. The isoelectric point of pumice was at pH 2.70. It was found that monovalent cations and mono-, di-, and tri-valent anions were indifferent electrolytes for pumice particles, on the other hand, di- and tri-valent cations were potential determining cations for them.

The measurement of carbon dioxide transmission of edible films by a static method

A static method is proposed for the measurement of CO2 transmission of edible films. It is based on the absorption of CO2 transmitted through the film on an absorbent ascarite II. Water is evolved during absorption of CO2 by ascarite II and that is absorbed by a desiccant, anhydrous CaCl2. Total CO2 transmission is determined from the increase in weight of the absorbents. The transmission parameters, CO2 transmission rate (CO2TR), CO2 permeance and CO2 permeability (CO2P), are also calculated. The edible film used was composed of methyl cellulose and polyethylene glycol. An attempt was made to determine the optimum amounts of ascarite II and CaCl2 to be used. Finally, the effect of CO2 pressure on the transmission parameters was also examined. CO2TR was found to increase with increasing pressure while CO2 permeance and CO2P values were found to decrease with increasing pressure.

Control of aroma transfer by biopolymer based materials

Abstract Biopolymers such as proteins offer unique functional properties that can be used in the field of edible or biodegradable active packagings. Among the barrier properties of biopolymer based packaging, the knowledge of the aroma compound transfer is required (i) to control losses and sorption of aroma compounds which are important contributors to the sensory product quality (ii) or to emit desirable flavour from active packaging in a controlled way. Permeability of 2-heptanone in protein coated papers was investigated. It was demonstrated that coating by gluten or casein decreased the permeability of 2-heptanone and that coated papers had promising aroma barrier compared to other packaging materials such as sulphuric or paraffin papers or LDPE. The ability of biopolymer films to control aroma release was also demonstrated. An aroma compound (carvacrol) was incorporated in a gluten protein matrix, which showed adequate ability to maintain aroma compounds during film processing. The release of the aroma compound into the headspace was followed under accelerated conditions of temperature and relative humidity (30°C and 60% RH). It was shown that the release rate was not dependent on carvacrol amount. The gluten film delayed aroma compound emission into the headspace for more than a month.