Effects Of Deacetyl Konjac Glucomannan On Gelatinization And Retrogradation Properties Of Wheat Starch

Since the poor gelatinization properties of natural wheat starch(WS)and the retrogradation of starch gel,the flavor and quality of some wheat starch-based foods deteriorated during the storage period.Therefore,it was of great significance to control the gelatinization and retrogradation of WS in food processing.Konjac Glucomannan(KGM)as a common food additive has high application value in the food industry.Deacetylation treatment effectively improve the gelation,thermal stability and film-forming charactetics of KGM,which broaden the application of KGM in the food processing field.At present,there are many studies on the combination of starch and hydrocolloid,but the effect of deacetyl konjac glucomannan(DKGM)on the gelatinization and retrogradation properties of wheat starch need further studies.Therefore,the objectives of this study were to investigate the effects of DKGM on the gelatinization and retrogradation properties of WS.The main results were as follows:1.Physicochemical property determination and structural characterization of konjac glucomannan with different degrees of deacetylation.With the increase of deacetylation degree,the viscosity and water holding capacity of KGM decreased significantly(p<0.05),and the thermal stability was improved.Fourier transform infrared spectroscopy(FT-IR)showed that the acetyl characteristic peak of DKGM around 1735 cm^-1 gradually weakened with the increase of deacetylation degree.X-ray diffraction(XRD)patterns displayed that KGM had a relatively obvious diffraction peak near 20°.However,two diffraction peaks in the XRD pattern of DKGM were observed near 11.96°and 20.07°,and the peak intensity presented strengthened trend with the increase of deacetylation degree.Scanning electron microscope(SEM)images indicated that deacetylation changed the micro-morphology of KGM,and the removal of acetyl group made the surface from smooth to rough.When the different degree of deacetylation(DD)was 72.70%,the micro-morphology of KGM was damaged obviously.2.Effects of deacetyl-KGM on gelatinization properties of wheat starch.KGM with or without deacetylation treatment both raised the peak viscosity(PV),trough viscosity(TV)and final viscosity(FV)of WS-DKGM mixed systems.The setback(SB)values of WS-DKGM mixed systems significantly decreased(p<0.05)in comparison with native WS and showed a positive correlation with the degree of deacetylation of KGM.The steady shear results demonstrated that all samples were Non-newtonian fluids and showed shear-thinning behavior.Dynamic viscoelasticity measurements indicated that the storage modulus(G?)of WS-DKGM gels was elevated in the presence of DKGM,suggesting that DKGM effectively improved the elasticity and promoted the network formation.3.Effects of deacetyl-KGM on retrogradation behavior of wheat starch.During the storage at 4°C for 7 days,the hardness of these gels showed a downward trend,suggesting the syneresis and recrystallization of starch.But the addition of KGM with deacetylation delayed the process of starch retrogradation,which was further verified by the low-field nuclear magnetic resonance(LF-NMR)and XRD data.Similarly,the growing rate of retrogradation enthalpy(?H_r)of mixed gels were slowed down as the deacetylation degree of KGM increased.FT-IR results displayed that the addition of DKGM reduced the orderliness of WS after stored at cold temperature.The above results suggested that the addition of DKGM effectively inhibited the retrogradation rate of WS.4.Effects of deacetylated Konjac Glucomannan on the quality of“Liangpi.”The hardness,chewiness and cohesiveness of“Liangpi”added with DKGM(DD=72.70%)were significantly lower than those of the blank group,and chewiness and cohesiveness showed a descending trend with the ascending of DKGM addition(0?3%).In the sensory evaluation,the toughness and viscosity scores of“Liangpi”were higher than those of the blank group(p<0.05).When the addition amount was 3%,the toughness and viscosity scores increased significantly(p<0.05).In vitro digestion experiment,with the increase of DKGM supplemental level(0?3%),the content of RDS in“Liangpi”declined while the RS was ascended.These results suggested that DKGM enhanced the anti-digestion performance of liangpi and was helpful in reducing the postprandial blood glucose level.