D Characterization Of Chemically Modified Chinese Yam Starch And Film-forming Properties Of Derivatives

In this thesis,fresh yam was used as raw materials,Optimal condition was obtained by single factor and orthogonal test and the optimal conditions of extraction of yam starch were temperature 45℃,pH9.5,solid-liquid ratio 1:11(w/v)and washing seven times.The scanning electron microscope(SEM),particle size analyzer,Rapid Visco Analyzer(RVA),differential scanning calorimetry(DSC)and other technology were used to observe Particle morphology,size distribution,gelatinization properties,viscosity of starches.Chemically modified Chinese yam starches were prepared with different amounts of propylene oxide,sodium trimetaphosphate(STMP)and sodium tripolyphosphate(STPP)showed different pasting temperature,viscosity,transparency.Starch films showed different mechanical properties and transparency.The FTIR can verifed that chemical reaction was occured between etherifying agent,crosslinking agent and starches.In comparison with the native yam starch,the surface of chemically modified Chinese yam starches were appeared significant embossment and dent.They were smooth and had no fissures.This may be due to propylene oxide,STMP and STPP are relatively modest modification reagent.It was also observed that the median diameter of native yam starch(NYS)was 22.98 um,which less than chemically modified yam starches,that was consistent with SEM.The crystalline types of native yam starch(NYS),modified yam starch(MYS)and dual-modified yam starch(DMYS)were C-type.However,the peak of MYS and DMYS at 6.30 was weaken than NYS.Result shows that the modification mainly in the non-crystalline regions of starch.The peak shape,in the 1150 cm-1 was C-0 and C-C and in 1000-1100 cm-1 was P-O and P=O.FTIR showed the peak shape of chemically modified yam starches was stronger in the 1150 cm-1 and 1000-1100 cm-1,that indicated the modifiction was occurred.Viscosity and gelatinization properties of MYS and DMYS were affected by the content of propylene oxide and the type of crosslinking agent.Gelatinization temperature and final viscosity of NYS were 79℃ and 5702cP,respectively;it was higher than corn and wheat starches.The gelatinization temperature and final viscosity of HPC1,HPC2 and HP were in the range 75.1-70.4℃,99-496cP,75.9-69.2℃,523-4100cP,74.2-68.8℃,4499-3624cP,which were lower than NYS.The final viscosity of HPC1 and HPC2 was increased with the volume fraction of propylene oxide increase.However,the gelatinization parameters showed an inverse trend.The peak viscosity of starch modified with propylene oxide was higher than that of NYS.The granular surface of MYS and DMYS appeared significantly embossed and indented.MYS film treated with 12%propylene oxide showed a more homogeneous fractured surface and best transparence.The final viscosity of HP6C1 and HP6C2 was 27cP and 45cP,which was too low to form starch film.