Low-pressure plasma modification of the rheological properties of tapioca starch

Starch is an important biopolymer widely used in the pharmaceutical, food and textile industries. In this study, low-pressure (0.5 atm) cold plasma was used as an novel technique to modify the rheological behaviours of native tapioca starch using four different feeding gases (air, carbon dioxide, argon, and helium). The induced changes in starch samples were studied by rapid visco analyser (RVA), Rheometer, Fourier transform mid-infrared (FTIR) spectroscopy and scanning electron microscope (SEM) images, respectively. The plasma significantly (P < 0.05) increased peak viscosity, trough viscosity and breakdown viscosity of the treated starch compared to the control. FTIR spectral absorption peaks of the different plasma treated samples were observed at 924, 994, 1149, 1335 and 3274 cm⁻¹, which are related to C–O–C asymmetric stretching, C–OH bending, C–O–C asymmetric stretching, C–H bending and O–H stretching bonds, respectively. The differences in absorbance intensity at these frequencies revealed chemical changes in the corresponding functional groups. The results of FTIR spectral data support the theory that cross-linking reactions occur between starch molecules during plasma treatment, resulting in changes of pasting and rheological properties. However, there was no obvious fissures or cavities observed on the surface of starch granules observed using SEM imaging.