Pasting properties of cassava starch modified by heat-moisture treatment under acidic and alkaline pH environments

Abstract

Effect of pH adjustment before heat-moisture treatment (HMT) on pasting properties of modified cassava starch was investigated. After soaking in acidic water, cassava starch contained smaller molecules, while starch soaked in alkaline water had a more negative charge. These starches with a moisture content of 25% were subsequently heat treated at 100 °C for 16 h. Pasting profile analyses revealed that starch modified by HMT without pH adjustment (HMT_water) had a much higher viscosity than those adjusted pH to 11 and 3 prior to HMT (HMT_pH11 and HMT_pH3). Granules of HMT_water were completely disrupted, whereas the gels of HMT_pH3 and HMT_pH11 still contained particulates that distributed in dispersed starch chains. The appearance of gels varied from sticky with a springy surface for HMT_water to white-turbid, non-sticky and spoonable (yoghurt-like) for HMT_pH3 and brown-turbid, non-sticky, stable and spoonable (pudding-like) for HMT_pH11. These appearances correlated to their gel morphologies and starch structures before HMT.