Effects of wet-media milling on multi-scale structures and in vitro digestion of tapioca starch and the structure-digestion relationship

This work aims to understand the relation between multi-scale structural changes and in vitro digestion of tapioca starch modified by wet-media milling. The native starch granules were smooth and difficult to digest due to the hindrance of enzymes entry into the granules by the concentric shell architecture. However, 1-min milling could break the smooth surface of starch granules, weakening shell architecture and increasing k1 (digestion rate). Moreover, 5-15-min milling could greatly disrupt the short-range ordered structure and transform it into the amorphous phase to enhance k1. The increase of milling time to 30-420 min mainly interrupted the glycosidic bonds of the amorphous phase, allowing the production of amylose and amylopectin fragments, achieving continuous increase of k1. Despite the increasingly severe damage caused by milling to multi-scale structures, the disruption of shell barrier on the starch surface was the most critical for digestion, followed by short-range ordered structure breakage.