Reaction efficiency enhancement of hydroxypropylated tapioca starch

Abstract

The hydroxypropylated tapioca starch was synthesized by etherification of starch and propylene oxide in the presence of sodium hydroxide. All the reactions were carried out with 40 wt% tapioca starch in solution at 40℃. The variables of this reaction in water, i.e. the concentration of sodium hydroxide, sodium sulfate and propylene oxide and reaction time were studied by varying one variable at a time as the others were kept constant. When the concentration of sodium hydroxide, sodium sulfate and propylene oxide increased, degree of substitution and reaction efficiency were higher. Although, the degree of substitution and reaction efficiency were increased with the reaction time but appropriated constant at 24 hours. Then the series of reactions with different concentration of sodium hydroxide, sodium sulfate and propylene oxide were carried out at 40℃ for 24 hours. Three level factorial design was used for assigning the concentration of sodium hydroxide, sodium sulfate and propylene oxide for the individual experiment. There were thus 27 experiments, 3³ factorial experimental design, were performed using sodium hydroxide 1, 1.5 or 2%, sodium sulfate 10, 15 or 20% and propylene oxide 8, 14 or 20% based on the dry starch weight. Another series of reactions in aqueous ethanol was also investigated using the same condition designed for reactions in water but no sodium sulfate was added and various percentages of ethanol in water 30, 50 or 70% were attempted. The degree of substitution of the hydroxypropylated starches were determined by ¹H-NMRtechnique. Their corresponding reaction efficiency were obtained by calculating from the individual degree of substitution. All the reactions at each condition were repeated three times and the degree of substitution of each hydroxypropylated starch was average from their three repetitions, which was the means of three determinations. It was found that the condition of the reaction in water that gave highest degree of substitution of 0.2797 and reaction efficiency of 71.5% was sodium hydroxide 2% sodium sulfate 20% and propylene oxide 14% based on the dry starch weight. The pasting property of the hydroxypropylated tapioca starch with various degree of substitution was examined and compared with the native tapioca starch. It was revealed that the gelatinization temperatures of all hydroxypropylated starches was lower and the peak viscosity was higher than the native tapioca starch. In addition, the granule morphology the hydroxypropylated tapioca starch was about the same as the native tapioca starch indicating that the hydroxypropylated did not damage the starch granule.