Study On Thickening, Emulsifying Properties And Mechanism Of Chitosan

In China chitosan has been approved as a food thickener since 2007, but there is little information about the thickening mechanism and the relationship between thickening, emulsifying properties and structure of chitosan, which restricts the applications of chitosan in food industry. Therefore, on the basis of preparation of chitosan with narrow molecular weight distribution, the thickening rheological properties, interaction between chitosan and proteins as well as other food thicheners, emulsifying properties were investigated in this study to enhance the development and application of chitosan in food industry. This work will be of great importance for understanding the thickening mechanism and expounding the relationship between thickening, emulsifying properties and structure of chitosan. And it will also provide a solid theoretical basis for chitosan to develop functional food additive and ingredient.Measuring method of molecular weight of chitosan by gel permeation chromatography (GPC) was established:sample concentration of 4 mg/mL and the buffer of 0.2 M AcOH /0.15 M NH4OAc as the mobile phase. Preparing technique of chitosan with narrow molecular weight distribution through ultrasonic processed was investigated. Results showed that temperature, concentration of chitosan and acetic acid had great effects on the polydispersity of chitosan after ultrasonic processed;when the temperature was 24℃, the concentration of acetic acid was 0.27 mol/L and the concentration of chitosan was 1% according to the actual situation, the polydispersity was minimum and decreased from 11.51 to 4.25 after ultrasonic processed, while the degree of deacetylation(DD) of chitosan had not changed.Thickening rheological properties of chitosan solutions were investigated by studying the effects of molecular structure (molecular weight and DD), environment factors (concentration, shear rate, temperature, pH, ionic strength) on viscosity of chitosan solutions and intra-molecular interactions in solutions. Results showed that viscosity increased with the increase of molecular weight (Mw) and initially decreased and then increased with the increase of DD, reached the minimum at 70.8% within the range DD60.5% to 86.1%. Chitosan solutions exhibited shear thinning behavior. Viscosity increased with the rise of concentration, decreased with the increase of temperature and initially decreased and then increased with the increase of pH between 3.9 and 5.9, reached the minimum at pH 4.9. With the increase of ionic strength viscosity of chitosan solutions decreased excessively. Electrostatic interactions and hydrogen bonding forces are main forces in chitosan solution, which have great influence on viscosity of chitosan solutions. Viscosity of chitosan solution was related with the charged chitosan molecules and solution.Interaction between chitosan and salt-soluble meat proteins (SSMP) and thickening mechanism of chitosan were investigated by studying the effects of chitosan on the gel properties of SSMP. Results showed that chitosan could enhance the gel properties of SSMP. With the increase of chitosan concentration, storage modulus, penetration forces and WHC of SSMP gels increased proportionally. In the same chitosan concentration, storage modulus, penetration forces and WHC of SSMP gels increased with increasing amount of molecular Mw. When chitosan with DD77.3% was added, SSMP gels exhibited the highest storage modulus, penetration force and WHC. Microstructure of SSMP gels changed from granular structure to netwoks and texture of SSMP gels became more fine and uniform when chitosan was added. Interaction between chitosan and SSMP was confirmed by these results and the interaction mechanism was that chitosan contributed to the enhancement of texture of the SSMP gels by electrostatic interactions and hydrogen bondsInteracton between chitosan and other food thickeners were studied and complex gums containing chitosan were developed. Results showed that chitosan had no synergistic effects with other polosaccharides but had synergistic effects when the ratio of gelatin/chitosan was between 9:1(w/w) and 32:1(w/w).With the increase of Mw, viscosity and gel strength of complex gums increased while decreased with the rise of DD, and gel strength of complex gums was all lower than that of gelatin. Interaction between chitosan and gelatin was confirmed by the observation of dynamic rheological properties. When the ratio of gelatin/chitosan was 16:1(w/w) and the complex gums were added into the yogurt, the texture of yogurt was enhanced and the postacidification problem was solved.Emulsifying properties of chitosan were determined using turbidimetric method and integrated light scattering technique and the effects of chitosan concentration, molecular structure (Mw and DD), environment factors (pH, ionic strength) on emulsifying properties of chitosan were studied. Results showed that chitosan had excellent emulsifying properties. Comparison with 1% gum Arabic,1% chitosan exhibited the same excellent emulsifying activity and superior emulsifying stability. Emulsifying activity of chitosan initially increased, arrived at the peak at 0.75% and then declined, while emulsifying stability continuously increased with a rise of chitosan concentration from 0.25% to 1.25%. Emulsifying activity and stability of chitosan initially decreased and reached the minimum, then increased with the rise of DD. Chitosan with DD 60.5% and 86.1% showed superior emulsifying activity and stability. Chitosan with low Mw exhibited better emulsifying activity than those with high Mw and Chitosan with Mw 410 kDa and 600 kDa showed superior emulsifying activity in the test range. Emulsifying stability of chitosan increased with a rise of Mw. Emulsifying activity and emulsifying stability of chitosan increased with a rise in pH values from 3.9 to 5.9 and exhibited the superior emulsifying properties at pH5.9. And emulsifying activity of chitosan initially increased with consistent rise in ionic strength and reached a peak at ionic strength of 0.34mol/L and then decreased as ionic strength continued to increase while ionic strength had no distinct influence on emulsifying stability.In this study, the thickening rheological properties, interaction between chitosan and proteins as well as other food thicheners, emulsifying properties were elucidated on the basis of preparation of chitosan with narrow molecular weight distribution. The relationship between thickening properties and structure was cleared and the thickening mechanism of chitosan was initially revealed.