Transglutaminase-modified Properties Of Whey Protein-hydroxypropyl Methyl Cellulose Composite Films

Whey protein and hydroxypropyl methylcellulose were used as the main film-forming materials for edible packaging composite films modulated by transglutaminase(TG)and glycerol as the plasticizer.The mechanical properties,light transmittance,water vapor transmittance and solubility of films were taken as index,and the influence of the hydroxypropyl methyl cellulose,TG enzyme concentration and glycerol content on whey protein-hydroxypropyl methylcellulose composite films were examined,and the significant impact factor for mechanical properties was selected for optimization of composite film-forming conditions.The structure and properties of films prepared were analyzed using SDS-PAGE electrophoresis test,fourier infrared spectrometer(FT-IR),color difference meter,the contact angle,rheometer,thermal stability(DSC)and scanning electron microscope(SEM),to reveal the modification effect of the hydroxypropyl methylcellulose and TG enzyme on whey protein based film.The main results are as follows:1.Optimization experiments showed that in comparision with whey protein film,the mechanical properties,light transmittance and solubility of the composite films improved to a certain extent under the condition of 3%HPMC,the amount of glycerol at 2.2-2.5:1(WPC/GLY,w/w)and enzyme concentration of 6U/g protein.2.SDS-PAGE results showed that compared to whey protein,TG enzyme induced whey protein to form covalently copolymer.The rheological property of film-forming solution was analyzed,and the results showed that the viscosity of polymer solution increased gradually with the HPMC content,TGase promoted the viscosity of composite film-forming solution increase at different addition of hydroxypropyl methyl cellulose.3.FT-IR analysis showed that of whey protein-hydroxypropyl methyl cellulose blend film structure changed compared with whey protein film,the absorption peak of blend film enhanced,After TG enzyme catalysis,absorption peak of whey protein film was enhanced,indicating self crosslinking of whey proteins induced by TG.4.Total difference in color of composite film increased gradually with hydroxypropyl methyl cellulose addition,but there was no obvious change after TGase catalysis.As for contact angle,there was no significant difference in WPC-HPMC blend film with the increase of HPMC content,then contact angles of crosslinked films increased,the smaller the contact angle was,the more hydrophilic was Thermal stability property of whey protein-hydroxypropyl methylcellulose crosslinked films were lower than the blend films.Through SEM analysis,the texture of alone whey protein film and hydroxypropyl methyl cellulose film were relatively uniform and smooth,comparing with the blend films.The surfaces of the blend films became rough with cellulose addition and that of composite films were smooth upon TGase catalysis.5.After HPMC content increased from 5%to 25%,the light transmittance of blend films decreased,there were no significant changes in water vapor permeability,and elongation decreased,tensile strength increased,the viscosity of film solution increased significantly,the infrared absorption spectral band widened and moved towards the high wave number when HPMC addition of 15%-25%,indicating that intermolecular hydrogen bond of whey protein and hydroxypropyl methylcellulose enhanced.The surface of films became rough,some films has holes and crack phenomenon.After TG enzyme catalysis,the solubility of all composite films decreased,elongation and tensile strength improved,crosslinked films formed dense and uniform structure and relatively smooth surface.