Food Protein-Chitosan Interaction And Its Application In Food System

The exploitation of protein-polysaccharide interactions offers opportunities for thedesign of new food structures with different functional properties and it has been of greatconcern in food research field. As the second largest abundant natural polysaccharide in theworld, chitosan (CS) and its derivatives shows wide application prospect due to its cost andfunctional properties. So far, the investigations regarding using food protein-chitosaninteraction to tailor the food structure are limited, especially in soy protein-based foodsystem.Consequently, this thesis systematically studied the effect of pH, mixing ratio, ionicstrength and temperature on the mechanism of interaction between food protein and chitosan.The formed complex and coacervate with different functional properties were theninvestigated in food emulsion and food gel to show their application. The main results are asfollows:(1) This study explored the interaction between the β-conglycinin (7S) and glycinin (11S)and chitosan (CS) and investigated the influence of pH (pH3-8), mixing ratio (0.05、0.1and0.2g g-1), chitosan molecular weight (150、350and500kDa), ionic strength (100mM) andheat treatment (95°C). The turbidity versus ζ-potential pattern showed that, independent ofprotein, the coacervation of7S-CS and11S-CS mixtures were all obtained at chargeneutralization pH while soluble complex were all obtained atζ-potential of+20to+30mV,indicating the7S-CS and11S-CS mixtures were electrostatically driven. The molecularweight of chitosan showed less effect on the stability of mixtures. Mixing ratio as well as heattreatment and ionic strength, however, showed great effect on the stability of mixtures.(2) The formation and interfacial adsorption of11S-CS soluble complex wereinvestigated at acidic pH. The stability of the mixed emulsion stabilized by the complex wasalso evaluated at pH4.5. Turbidimetric analysis, isothermal titration calorimetry (ITC) anddynamic light scattering were used to characterize the dynamic formation of the complex. Theresults showed that soluble complexes were formed at pH4.5and saturated at mixing ratio of0.1g g-1, showing theζ-potential of+27.95mV. It also can be found that the soluble complexshowed improved interfacial adsorption. The droplet size and confocal observation of themixed emulsion fabricated with11S-CS soluble complex displayed improved stability at mixing ratios of0.1-0.2g g-1, suggesting the synergistic effect of the two molecules. Weconcluded that interfacial and emulsifying properties of glycinin could be improved byformation of11S-CS soluble complex at acidic pH.(3)To fabricate a soy protein emulsion with good storage stability against microorganism,we investigated the stability and antimicrobial activity of7S-CSmixed emulsion at acidicpHs.Results of droplet size and microstructure showed7S/CS mixed emulsions were stable atacidic pHs. Agar well diffusion experiment suggested that the mixed emulsions inhibited allthe microorganisms (S. aureus, B. subtilis, E. coli andSalmonella).As for the storage test,results showed that7S-CS mixed emulsion displayed an significantly (p <0.05) improvedstorage stability than control both under un-inoculated and inoculated condition because thepresence of chitosan. The fabrication of7S-CS mixed emulsion illuminated a new idea thatantibacterial agent can be used on the oil-water interface and can play a multifunctional rolein increasing acidic stability and antimicrobial activity of emulsion in order to extendshelf-life.(4) The SPI-CS coacervation and its application in inhibition of lipid oxidation wereinvestigated. Results showed that the coacervate formed between the negatively chargedcarboxyl group on SPI and the positively charged amino group on CS. The coacervates withhighest viscosity were formed at pH6.5-7.0, mixing ratio0.1-0.2g g-1, showing a weakgel-like rheological properties (G’> G"). A coated emulsion with high encapsulationefficiency can be fabricated in this way thereby reducing the lipid-air contact and inhibition oflipid oxidation.(5)This study explored the microstructure, textural and physical properties of WPI-CSmixed gels at pH3.5and4.0. The results of microstructure showed that WPI-CS mixed gelsdisplayed a total different gel structure at different pH. Phase-separated gel structure wasobtained at pH3.5while coupled structure was obtained at pH4.0because differentinteraction occurred. Ionic strength showed greater effect on coupled gel. The results in thispaper suggested that segregative phase separation can be used to alter the fracture and waterholding properties of WPI gels formed below their pI, in a way similar to that seen above theirpI, indicating that the microstructure decide the textural and physical properties. WPI-CSmixed gels with protein continuous network showed higher gel strength and water holding value while mixed gels with coarse stranded network showed poor gel strength and waterholding value.(6) A stable positively charged (+30mV) chitin microfiber (CMF) suspension wasfabricated by a facile Microfluidizer approach without changing its chemical structure. Theobtained CMFwere then developed in a transglutaminase cross-linked7S gel.Themorphological and rheological characterizations of the7S-CMF gels were done as a functionof the protein and CMF concentrations. Results showed that the presence of CMF networkimproved the gel strength significantly. This effect was CMF content dependent and wasrelated to the formation of sponge-like porous microstructure. We inferred that the CMFprovided an initial framework for gel formation and added structural rigidity to the protein gel.The role of protein was to participate in network development as an electrostatic coating andgelation component.