Studies On The Rheological Properties Of Sodium Caseinate,Fenugreek Gum,N,O-carboxymethyl Chitosan And Complex Hydrogel

Natural polymer, as food additives and drug carriers, are widely used in the food and pharmaceutical fields. Rheological properties play an important role in food texture, storage, transport and processing, while the sol-gel conversion process and the gel properties provide important technological support for preparation of drug carrier. Rheological properties of sodium caseinate(SC), fenugreek gum and N,O-carboxymethyl chitosan were firstly studied in this paper, and then the pH-sensitive hydrogel composed of sodium caseinate(SC) and N, O-carboxymethyl chitosan was prepared. The gelation process and structure formation were also analyzed by structure parameters. The hydrogel have not been reported by other literatures,therefore, the paper aimed at providing rheological properties of polymers and preparing a new hydrogel which could be used for application in food and medicine.The research contents were based on: 1) measurement of steady-shear flow properties to find a well rheology model; 2) evaluation of the thixotropy and dynamical viscoelasticity properties at different concentrations; and 3) comprehensive analysis of the rheological properties using multiwave-temperature ramp test under the condition of temperature and frequency changed synchronously. 4) Gel formation, gel strength and structure formation were also investigated.1.Steady-shear flow, thixotropy and dynamical viscoelasticity tests were systemically carried out under a range of SC concentration(0.01~25%, w/v) and temperature(0~80 °C). The results showed that SC solutions exhibited two different flow behaviors due to the variation of concentration. Shear-thinning regions were observed and found to be well correlated to the Cross model for high concentrations of SC(>15%, w/v). Moreover, the pseudoplastic behaviors exhibited concentration dependence, i.e., the behaviors increased with the rise of concentration. However,when the concentration of SC was below 15%(w/v), the system exhibited obvious characteristic of Newton fluid. Dynamical viscoelastic properties showed a transition from gel-like to fluid-like structure with the decrease of frequency, and the appearance of cross point was dependent on the concentration of SC. The variation of the hysteresis loops area suggested a stronger thixotropic behavior as the polymerconcentration increased. Multiwave temperature ramp test for 20%(w/v) SC solution showed the viscoelasticity behavior had a strong dependence on temperature rather than frequency, which was consistent with previous results.2. Steady-shear flow, thixotropy and dynamical viscoelasticity tests were systemically carried out under a range of FG concentration(0.05~2.0%, w/v) and temperature(0~80°C). The results showed that FG aqueous solutions exhibited Newtonian plateaus followed by shear-thinning regions which were found to be well correlated to the Carreau model. It was also found that the pseudoplastic behaviors of the FG aqueous solutions exhibited a concentration dependence. When the concentration of FG was above 1%(w/v), the system exhibited a gel-like behavior.Dynamical viscoelastic properties also showed a solid, elastic-like viscoelastic behavior. The variation of the thixotropic index ? showed a stronger thixotropic behavior as the polymer concentration increased, which indicated a typical elastic behavior of FG solutions with high concentration. Multiwave temperature ramp test for 1.0%(w/v) FG aqueous solution showed that the solid-like behavior had a strong dependence on frequency rather than temperature, which was consistent with the results of oscillatory frequency sweep test. These results could provide a useful indicator for the applications of FG in food industry and other fields.3.The flow behavior, thixotropy and dynamical viscoelasticity of N,O-carboxymethyl chitosan solutions were measured by steady-shear and small-amplitude oscillatory experiments, respectively. Power-law and Cross models were used to analyze the flow properties of the systems. The results showed that N,O-carboxymethyl chitosan solutions exhibited two different flow behaviors due to the variation of concentration. When the N, O-carboxymethyl chitosan solutions was in low concentrations(0.01%~1%, w/v), the systems exhibited obvious characteristic of Newton fluid. However, shear-thinning regions were observed and found to be well correlated to the Cross model for high concentrations of N, O-carboxymethyl chitosan solutions(5%~15%, w/v). The variation of the hysteresis loops area suggested a stronger thixotropic behavior as the polymer concentration increased. Dynamical viscoelastic properties showed a transition from fluid-like(G?>G?) to gel-like(G?>G?)structure with the increase of frequency, and the appearance of cross point was dependent on the concentrations of N, O-carboxymethyl chitosan solutions.4.The pH-sensitive hydrogels composed of sodium caseinate(SC) and N,O-carboxymethyl chitosan(NOCC) were prepared and a new method to characterize the gelation process was presented in this work. Reological tests suggested that RSC/NOCC = 3/7(the weight ratio of SC and NOCC) was the best ratio of hydrogel. The well-developed three-dimensional network structures in the hydrogel were confirmed by AFM. Two structural parameters, tIS and tCS, denoted as the initial and critical structure formation time, respectively, were used to provide an exact determination of the start of structure formation and description of gelation process. The gelation process strongly depended on temperature changes, a high temperature resulted in an early start of gelation. The non-kinetic model suggested the higher activation energy in the higher temperatures was disadvantageous to structure formation, and vice versa.Due to the smart gel reported here was very stable at room temperature, we believed that the gel could be used in drug delivery in the future.