Effects of starch gelatinisation on the thermal, dielectric and rheological properties of extruded corn masa

The effects of processing on starch gelatinisation of corn masa prepared by extrusion were monitored by observing the changes in thermal diffusivity, starch crystallinity, peak viscosity and the differential dissipation factor (DDF). The results show that there is a threshold processing temperature (Tc), about 80 degrees C, above and below which different behaviour patterns for the measured properties are observed. The thermal diffusivity, starch crystallinity and the position of a peak in the DDF have a maximum at approximately Tc=80 degrees C. The peak viscosity decreases monotonically for Tc up to 80 degrees C and then remains constant. On the bases of textural characteristics of masa and tortilla, this work indicates that the degree of starch gelatinisation in the extruded masa is optimum at temperatures at approximately 80 degrees C where the room temperature thermal diffusivity and differential dissipation factors have maximum values. Textural analysis made in tortillas with masas prepared at various temperatures support the above conclusions. (C) 1998 Academic Press Limited.