Effect of salt on the glass transition of condensed tapioca starch systems

- Sodium and calcium ions interact with condensed tapioca starch to alter structural characteristics.
- Sodium and calcium interactions produce distinct mechanical properties from the starch-water matrix.
- Sodium and calcium ions are equally effective in increasing the Tg of condensed tapioca starch.

This work examines the effect of including hydrated NaCl and CaCl2 (up to 6% w/w) on the physicochemical properties of condensed tapioca starch. Samples were prepared by hot pressing at 120 °C to produce condensed systems that covered a range of moisture contents from 7.34% w/w (23% relative humidity) to 19.52% w/w (75% relative humidity). Tensile storage modulus and heat flow measurements were taken using DMA and MDSC, which were accompanied by FTIR, WAXD and ESEM. Increasing the salt level enhances the mechanical strength of starch in the glassy state and shifts the glass transition temperature to a higher value. Antiplasticising effects of NaCl and CaCl2 on the non-phosphorylated tapioca starch are indistinguishable from each other. Observations are complemented by intensification of absorbance peaks in FTIR spectra and a systematic change in shape and intensity of diffraction patterns with increasing addition of salt consistent with interactions between added ions and macromolecule.