ساختار و شرايط تشكيل كمپلكس بين صمغ كتيرا و پروتئين بتالاكتوگلوبولين

چكيده انگليسي :

Structure and Conditions of Complex Formation between Tragacanth Gum and Lactoglobulin Mahla Amir m amir@ag iut ac ir October 18 2010 Department of Food Science and Technology Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Ali Nassirpour Ali Nasirpour@cc iut ac ir Abstract Polymer interactions are used in a variety of fields i e medical biochemical food science and polymer chemistry Interactions between oppositely charged proteins and polysaccharides are of particular interest in food science especially with respect to functional foods The nature of interactions between proteins and polysaccharides whether repulsive or attractive will lead to different behaviors as segregative or associative phase separation respectively The associative phase separation can be a consequence of a complexation process Such phenomenon is initiated at themolecular scale through attractive electrostatic interactions between one polysaccharide molecule and one or more protein molecule When two polymers are oppositely charged an electrostatic complex can be formed The electrostatically bound complexes can be either soluble or insoluble The insoluble complexes concentrate in liquid coacervate droplets that further coalesce and phase separate to form a separate coacervate layer As a result one phase of the mixture is concentrated in the two polymers and the other phase contains mainly the solvent Proteins and polysaccharides are widely used in food products As the two biopolymers are often used simultaneously understanding their interactions has great importance in control of structure and texture of manufactured foods In this study interactions between lactoglobulin BLG and tragacanth gum TG were studied in aqueous solution at pH ranging from 3 5 to 5 5 and at different concentrations of the biopolymers BLG and TG solutions were prepared in distilled water under gentle stirring at 20 C The dispersions were kept at 4 C for 18 h to allow complete hydration of biopolymers Different biopolymers concentrations were mixed and pH value was adjusted by HCl Absorbance of the mixtures were measured at 650 nm using spectrophotometer The measured absorbances were plotted against pH After mixing of biopolymers in specific ratios and adjusting pH value the phase diagram was obtained In this study pHC pH and pHopt were identified and measured for different biopolymers solutions The formation of intrapolymer complexes is believed to be initiated at pHc By decreasing pH value of the biopolymers mixture firstly the biopolymers complexes were observed and mixture absorbance was increased When pH value was dropped under certain value phase separation was observed The pH at which complexes or phase separation occurred depended on protein polysaccharide ratios and by increasing BLG quantity in the mixtures critical pH was near the isoelectric pH of BLG Result showed that TG has an interesting phase diagram comparing other gums and phase diagrams of BLG and TG showed that the phase separation observed during experiments is an association phase separation Rheological studies showed an increase in viscosity in first step of solutions complex formation and after that the viscosity of biopolymers mixtures solutions were decreased This is because at pH molecular shrinkage complex association and phase separation were occurred Complex sizes increased between pHC and pH because of soluble complexes formation and a decrease in complex sizes was observed and this decrease in caused by neutralization of initiate complexes and solubilization of biopolymers complexes This wide range complex formation helps product developer to use tragacanth gum in a large range of formulations Keywords Protein polysaccharide interactions Associative phase separation Electrostatic interactions Phase diagram Light scattering Rheology

امير، مهلا

ساختار و شرايط تشكيل كمپلكس بين صمغ كتيرا و پروتئين بتالاكتوگلوبولين

واكنش هاي پروتئين-پلي ساكاريد , جداشدن فاز با تجمع ذرات , واكنش هاي الكترواستاتيكي , فاز دياگرام , پراكنش نوري , رئولوژي