Physicochemical Properties And Structure Characterization Of Cassava Starch Phosphate

Starch phosphate (SP) is one kind of starch derivative produced from esterification of starch and phosphate. SP with low degree of substitution(DS)(DS≠0.02) was usually applied in the past. Now SP with higher DS(DS>0.02) is widely used in paper-making, textile, food industry and so on. So the investigations about synthesis, structures and physicochemical properties of SP with high DS are becoming more and more important.Firstly, mixture of orthophosphate (MP) or sodium tripolophosphate (STP) was used as esterifying agent in preparation of cassava starch phosphaite by dry process. The effects of different reaction conditions on DS and reaction efficiency (RE) were testified by single factor experiments. The influence factors include amount of esterifying agent, reaction temperature, reaction time, reaction pH and amount of urea. Results show that the optimum reaction conditions for preparing SP with high DS by dry process as follows: the range of reaction temperature was 140~150℃, the reaction time was 2h, the pH was 5.0 and the range of urea amount was 4%~5%. By adjusting the amount of esterifying agent, SP with DS 0.02~ 0.09 can be prepared easily while RE is about 60%~ 70%.Secondly, the structures of cassava starch phosphate were characterized by infrared spectrum (FTIR), scanning electron microscopy (SEM), x-ray diffraction (XRD), differential scanning calorimetry (DSC) and analysis of starch-iodine compound absorption spectrum. Furthermore, its physicochemical properties were investigated. Structure analysis indicated that -PO4 groups were added in glucose units of starch but it can't be manifested in the FTIR spectra. There were a certain of dents and splits on SP granules surface. Esterification of starch not only occurred in the amorphous region of starch granule, but also damaged its crystalline region. After esterification of starch, the pasting temperature will decrease and the pasting enthalpy get lower and the range of pasting temperature will get narrow. And partial starch chains were ruptured and partial helix structures of starch were destroyed. The experimental results of SP physicochemical properties indicated that cassava starch paste and SP paste were of the pseudoplastic characteristics. Viscosity of SP paste was relatively stable in high(95℃) or low(55℃) temperature. Transparency of SPpaste with DS ≤0.084 was higher than that of cassava starch. Retro gradation and freeze-thaw stability of SP paste were improved.Finally, the feasibility of preparation cassava starch phosphates by dry process was discussed. The costing and the economic balance about SP prodution and marcketing were evaluated.