Synthesis and characterisation of phosphorylated sago (Metroxylon sagu) starch

Abstract

Sago (Metroxylon sagu) starch is a main carbohydrate source in many areas of Indonesia, Papua New Guinea, and Malaysia. It is isolated from the trunks of wild and cultivated sago plants spread over South East Asia. Sago yields higher amount of starch (2-3 tons/ha-year) compared to other crops such as cassava or maize, and therefore is a potential source of raw material for modified starch industry. In particular, sago starch has the potentiality to be used as a raw material for the the preparation of commercial food thickeners. In this research, sago starch was phosphorylated to give products with improved thickening properties. The chemical modification was performed at temperatures of 110-130°C and pH level of 9, using a mixture of sodium tripolyphosphate and sodium tripolyphos (STPP and STMP, weight ratio of STPP/ STMP= 7.5:3) and an intake of 7.5%-weight STPP based on dry starch. The experimental result shows that the Degree of Substitution (DS) of the phosphorylated products is accessible in the range of 0.006-0.011. The pasting properties of the product has been characterised using Rapid Visco Analyzer (RV A) instrument. The peak and final viscosity of phosphorylated sago starch (2471 cP and 1695 cP, respectively) are significantly higher compared to peak viscosity (1246 cP) and final viscosity (962 cP) of native sago starch. The swelling power of phosphorylated sago starch (5.77 gig) is also higher compared to native sago starch (3.78 g/g). The result suggests that phosphorylation is a promising method to modify sago starch for food thickener applications.