Effect of enzymatic pretreatment on the synthesis and properties of phosphorylated amphoteric starch

Phosphorylated amphoteric starch was prepared from enzyme-modified tapioca starch in the aqueous alcoholic–alkaline medium. Optimization of the reaction parameters for maximum degree of substitution (DS) of phosphorylated amphoteric starch were carried out using response surface methodology (RSM). Optimum modification conditions were shown as following: NaOH concentration 3.71 g/100 g starch (dry basis), CHPTAC concentration 6.34 mL/100 g starch (dry basis), STP concentration 6.13 g/100 g starch (dry basis), water/ethanol ratio 1.16, reaction temperature 50 °C, reaction time 3 h, and the starch concentration 30%. Under the optimal condition, the maximum anion degree of substitution (DSA) and cation degree of substitution (DSC) were 0.0274 and 0.0408, respectively. Compared with the DS of the amphoteric starch prepared from native tapioca starch (NPTAS), the DS of the amphoteric starch from enzyme-pretreated tapioca starch (EPTAS) was higher at the same reaction conditions, suggesting enzymatic pretreatment improved the reaction processes significantly. Scanning electron microscopy and X-ray diffraction data showed that the granular shape and crystalline structure of EPTAS did not change. Compared with NPTAS, the pasting stability of EPTAS with the same DS was also significantly improved.