Extrusion of cassava starch with either variations in ascorbic acid concentration or pH

Thermal mechanical extrusion is used to make cassava products that are later expanded by frying. During extrusion the native starch granules are broken down and starch polymers degraded. This continuum of change to the starch has been termed starch conversion. Inclusion of ascorbic acid promoted starch conversion as measured by a range of techniques including measurement of water solubility, water absorption, hot paste and alkaline viscosities. It was found that the Rapid Visco Analyser (RVA, Newport Scientific, NSW, Australia) was particularly sensitive in the monitoring of the changes owing to extrusion. Expansion of the extruded product was increased at the higher starch conversions caused by ascorbic acid addition. Changes in; starch conversion were greater in the presence of ascorbic acid compared with general acid treatment at equivalent pi-Is. Although the general acidification did encourage more starch conversion there was no measured change in the expansion properties.