Maize starch biphasic pasting curves

The pasting of commercial maize starches was found to be a biphasic phenome non, exhibiting an expected first viscosity peak as well as an unexpected, relatively large second viscosity peak under specific cooking conditions wh en using a Rapid Visco Analyser (RVA). The second peak formed at long holdi ng times (between 32 and 45 min), holding temperatures within the range of 82 to 95 degrees C, starch concentrations from 8 to 13% with a wide range o f initial heating rates (0.5-10 degrees C/min) and shear conditions (150-50 0rev/min). The second pasting peak is attributed to the formation of comple xes between amylose and low levels of lipid present in maize starch. When l ipid was partially removed by extraction with methanol-chloroform (1:3 v/v) , the second pasting peak disappeared. When, however, the starch sample was treated with solvent and the solvent removed by evaporation, the second pe ak remained, but formed carlier. Increasing the holding temperature gave a slightly higher first viscosity peak, slightly earlier, and led to a decrea se in the area and height of the second viscosity peak. Increasing heating rate also led to an earlier, slightly higher first peak and earlier but low er second viscosity peak. Increasing starch concentration led to an increas e in height and area of both the first and second peaks and their, later oc currence. Increasing shear led to a decrease in height and area of both the first and second peaks and their later appearance. (C) 2000 academic Press .