| In the present study,glutenin(Glu)and gliadin(Gli)from wheat were modified by protein-glutaminase(PG)to obtain soluble glutenin(PG-Glu)and gliadin(PG-Gli).PGGlu or PG-Gli was added to potato starch(PS)at various levels(0.5%,1.0%,and 1.5% of starch weight,w/w),and the gelatinization,rheological,retrogradation properties and digestibility of potato starch/protein blends were investigated.Moreover,the possible interactions between potato starch and modified proteins were explored.Firstly,the effects of modified protein on gelatinization and rheological properties of potato starch were studied.Glutenin and gliadin modified by protein-glutaminase affected the pasting and rheological properties of potato starch effectively and the influence was closely related to the modified proteins concentration.Rapid viscosity analyzer(RVA)results indicated that the addition of PG-Glu and PG-Gli significantly decreased the peak viscosity,final viscosity and setback values of potato starch and the effect of the influence was increased with the increased concentration of modified proteins.Dynamic rheological measurements revealed that the storage modulus and loss modulus of potato starch were affected by PG-Glu and PG-Gli markedly,and the effect on the storage modulus was more obvious.Steady shear experiments indicated that the yield stress and consistency coefficient were decreased by the addition of PG-Glu and PG-Gli.The pasting and rheological properties of starch/protein blends indicated that the pasting and the swelling of potato starch granules were inhibited by the addition of PG-Glu and PGGli,which could be confirmed by the results of the confocal laser scanning microscope.Secondly,the effects of modified protein on the retrogradation and digestibility properties of potato starch were investigated.The short-term and long-term retrogradation of potato starch were promoted by the addition of PG-Glu and PG-Gli.The short-term retrogradation of potato starch was investigated by the rheological experiments,and the effects of modified proteins on the long-term retrogradation of potato starch were investigated by the DSC,LF-NMR,XRD,FT-IR and Raman spectrum.The enthalpy values of starch/protein blends were fitted to the Avrami equation,and the long-term retrogradation of potato starch was promoted by the modified proteins.The Low FieldNuclear Magnetic Resonance data showed that the motility of water in the potato starch decreased with the addition of PG-Glu and PG-Gli.The relative crystallinity of starch/protein blends calculated from X-ray diffraction pattern showed that the recrystallinity of potato starch was elevated with the increasing addition level of PG-Glu and PG-Gli.The in vitro digestion experiments of potato starch demonstrated that the RS content in the potato starch was elevated by the addition of modified proteins,and the fitting results of the first-order kinetic equation also revealed that the in vitro enzyme hydrolysis rate was depressed by the addition of PG-Glu and PG-Gli.The last part analysed the interactions between modified protein and potato starch.The hydrogen bonds between PG-Glu,PG-Gli and potato starch were researched through the rotational rheometer.The ultraviolet and fluorescence spectra results revealed that the hydrophobic interaction was the prominent interactions between PG-Glu or PG-Gli and amylose.The morphological distribution of potato amylose,potato amylopectin,amylose/PG-Glu,amylose/PG-Gli,amylopectin/PG-Glu,and amylopectin/PG-Gli blends were obtained by the atomic force microscope.The images showed that the aggregation of amylose was accelerated by PG-Glu or PG-Gli and the height of the clusters was obviously improved,which confirmed that PG-Glu or PG-Gli could promote the retrogradation of potato starch. |
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