Effect of cryo-milling on starches : functionality and digestibility

Four commercial starches, potato starch (PS), maize starch (MS), and two high amylose maize starches (HAMS), were cryo-milled, with and without hydration, for 20 min to study the effect of milling on physicochemical properties and enzyme digestibility. There was a significant increase in cold water soluble and damaged starch in cryo-milled samples in the order PS > MS > HAMS. Viscosity parameters of milled starches were significantly lower than for native starches, although changes in pasting temperature were not significant. In vitro digestion of native starches showed that enzyme resistance followed the order PS > HAMS > MS. A significant increase in enzyme digestion rate was observed after cryo-milling PS and HAMS but not MS. However, cryo-milled PS and HAMS were still less rapidly-digested than native MS. Scanning electron microscopy (SEM) of native, milled and digested starches showed a uniform 'inside-out' digestion pattern for MS, whereas a heterogeneous and nonspecific pattern was observed for PS and HAMS. This study suggests that milling has predominantly mechanical rather than thermal effects on starches and that the relative enzyme resistance of PS and HAMS granules compared with MS is due to the absence of the structural features of MS granules that allow internal access of enzymes.