Determination of thermo-rheological properties of okra mucilage

In this thesis, the mucilage portion of the okra which is a valuable product in terms of nutrition and health was obtained by ultrasound assisted extraction, and the structural, thermal and rheological properties of this polysaccharide extract were determined by chemical and physicochemical methods. In the determination of phase change enthalpy by investigating the glass transition temperature and enthalpy, the differential scanning calorimetry was used. At various solid / solvent ratios (1:10, 1:25 1:30 1:50) and extraction times of 5 and 30 minutes, the glass transition temperatures of the samples were found to be approximately 50oC and melting temperatures in the range of 166-170°C. Thermogravimetry (TG) and differential thermogravimetry (DTG) techniques were used to analyze the thermal stability of Okra polysaccharides and the results showed that the thermal stability of the okra mucilage was good. Thermal conductivity was measured by 3 ω method and it was determined that the thermal conductivity values of okra polysaccharide were not much different from water. FTIR analysis was carried out for the characterization of polysaccharides obtained by different extraction times and different rates of okra / distilled water, which provide detailed information about the composition of the extracts, to illuminate the bonds of polysaccharides. The main components of okra which were galactose, rhamnose and galacturonic acid can be observed in the FTIR analysis spectrum. In the study, flow behavior characteristics of the polysaccharides extracted at different okra / distilled water ratio (1:10 and 1:30), at different concentrations of polysaccharides (1%, 2, 3, 4; w / v) of the extracts at different temperatures (10, 20, 40, 60, 80oC) were investigated. The rheological properties were analyzed according to the Power Law model and the parameters were calculated. It was observed that okra polysaccharides showed non-Newton pseudoplastic flow characteristics. Flow behavior index varied between 0.234 and 0.947, and the consistency coefficient varied between 0.00437 and 0.2445 Pa.sn. The consistency coefficient (K), and the flow behavior index (n) decreased as the temperature increased. In the same way, the K value increases as the concentration increases. The flow behavior index (n) values did not show a regular behavior with concentration. The effect of temperature on apparent viscosities of okra polysaccharide samples was investigated at five different temperatures between 10 – 80oC. At the end of the measurements, a graph of change of consistency coefficient with temperature was drawn and the effect of temperature on the consistency index was modeled by the Arrhenius equation. In two samples with a 1:10 and 1:30 solid / solvent ratio, the activation energy increased as the concentration increased, and the highest activation energy value was reached for the 1:10, 4% concentration (275,8434 kj / mol). As a result, these polysaccharides can be used in the food industry as a thickening agent due to their adhesive and viscous structure and in the wastewater treatment systems with their high adsorption capacity, and their use as emulsifier and suspension agent in the fields such as pharmaceuticals.