Rheological characterization of corn starch isolated by alkali method

The pasting properties of alkali-isolated corn starches obtained from corn grits, as well as the rheological behaviour of their 8% gels were investigated. The alkali isolation was performed using different conditions concerning alkali concentration (0.15% and 0.30%), steeping time (30 min and 90 min) and temperature (25 °C and 50 °C).Alkali-isolated starches exhibited lower pasting temperatures and higher peak viscosities than the wet-milled starch. With respect to the steady shear measurements, alkali starch gels showed higher viscosities and greater extent of thixotropy.Changes in alkali isolation conditions did not influence the changes in gelatinization and peak temperature values. On contrary, peak viscosity was significantly influenced by these factors. Steady shear, as well as dynamic shear tests, showed that gels formed from starch isolated using higher alkali concentration were stronger than those obtained from starch isolated at lower alkali concentration. However, isolation at higher steeping temperature and longer steeping time resulted in starch with weak gel-like behaviour.

Isolation of starch by alkali method, instead of more conventional wet milling method, is more favourable due to economic and ecological reasons.However, the nature of alkali method, as well as the conditions during the alkali isolation, can influence the changes in pasting and rheological properties of starch. By detecting those changes, one can get better insight into the relationships between structure and flow, and thus establish handling and storage conditions of alkali–starch based products.Figure optionsDownload as PowerPoint slide