Resistant structure of extruded starch: Effects of fatty acids with different chain lengths and degree of unsaturation

This study investigated the formation mechanism of enzyme-resistant structures in extruded starch, specifically, fatty acid–starch complexes (FASCs). The effects of fatty acids (FAs) with different carbon-chain lengths (C12–C18) and degrees of unsaturation (C18:0–C18:2) on complex formation were evaluated, with fluorescence microscopy verifying complex formation. The complexed-lipid content and degree of relative crystallinity increased with the carbon-chain length and degree of FA unsaturation. FAs with fewer carbons were more likely to generate stable complexes (e.g., form II, melted at 100–120 °C), while FAs with more carbons tended to produce relatively unstable complexes (e.g., form I, melted at 80–100 °C). After reheating and cooling, a new amylose–lipid complex and an amylose-amylopectin network was formed in the unsaturated FASC samples, which restricted the penetration of enzymes into starch granules. A starch-linoleic acid complex exhibited the highest resistant starch content (15.7%) and lowest predicted glycaemic index (88.4).