The statistical data presented in Table 2 showed that WAI was affected by extrusion temperature (linear and square terms), NaOH concentration and interactions between these two variables. WAI increased when the NaOH concentration and temperature increased (Fig. 2). The effect of NaOH was more pronounced when the temperature was higher. These results indicated that the combined effects of extrusion and alkaline pH caused a granule structure modification that increased the hydration capacity. As previously shown in Fig. 1, when the NaOH level increased more phosphorus was bound and this conferred a greater stability on the starch granule. Lim and Seib (1993) observed that the conventional phosphorylation increased water uptake of starch derived from wheat and corn.