Acid and enzyme hydrolyses followed by ball milling were applied to fracture cassava starch granules. Microscopic and chromatographic evidence suggested different mechanisms of the two hydrolyses. Using the enzyme process, granules with a sponge-like structure and shells with the interior hydrolysed were produced. Amylose and amylopectin were subjected equally to multiple attacks by enzymes, with no significant change in granule crystallinity. The hydrolysed residues could not be effectively broken down by ball milling, although the crystallinity was destroyed. In contrast, the acid treatment caused superficial external corrosion, mainly at the amorphous lamellae, ie the branch points of amylopectin. Acid-lintnerised starch granules were mostly of Degree of polymerization, DP 10-15 and exhibited increased crystallinity and brittleness, making them more susceptible to breakdown upon milling. Ball milling, although destroying some degree of crystallinity, could effectively reduce the size of acid-hydrolysed starch, with no further degradation of amylodextrin molecules. By a combination of lintnerisation and ball milling, smaller particle starch (3-8 µm compared with 3-30 µm for native starch) could be produced. It is clear that removal of the amorphous phase prior to milling is critical for effective rupture of the granules.

Acid hydrolysis followed by ball milling was applied to cassava starch in order to fracture the granules. Lintnerisation led to degradation first in the amorphous domains and increased the crystallinity. The resulting increase in internal defects and brittleness made the granules more susceptible to breakage upon milling. Ball milling, although leading to some degree of crystallinity loss, could effectively reduce the size of acid-hydrolysed starch while the total double helix remained relatively unchanged. The resulting small-particle starch was structurally more heterogeneous (wider T m range). Swelling of small-particle starch was accompanied by solubilisation of water-soluble fragments at a temperature greater than 60°C. The properties of individual granules are strongly influenced by the hydration and physicochemical properties of their amorphous and crystalline domains.