Optimization of reaction conditions for resistant Canna edulis Ker starch phosphorylation and its structural characterization

Response surface methodology was employed to study phosphorous (P) and resistant starch (RS) content of resistant Canna edulis Ker starch phosphate monoester by starch phosphorylation with sodium mono- and dihydrogen orthophosphate. A five-level-four-factor central composite design was used for maximizing the P and RS content. The optimal reaction conditions obtained were NaH2PO4·2H2O to Na2HPO4·12H2O molar ratio of 1:0.44, phosphate sodium to starch weight ratio of 1.76:1, reaction temperature of 131.6 °C and reaction time of 2.43 h. The theoretical P and RS content were attained to about 0.58 and 73.17%, respectively. P and RS content experimentally obtained were 0.55 and 71.93%, in agreement with the predicted values. In addition, the structural characteristic of the purified starch phosphate monoester was investigated by 31P-nuclear magnetic resonance (31P-NMR), fourier transform-infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).