Structural and digestive properties of tiger nut starch-lauric acid complexes: Insights from multiscale...

Starch-lipid complexes were prepared using tiger nut starch (TNS) and lauric acid (LA) and characterized for their structural, physicochemical, and digestive properties. Multi-scale characterization techniques such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the addition of 7.5% lauric acid optimized the formation of V-type crystalline structures, achieving the highest relative crystallinity (21.58%) and the complex index (80.70%). Specifically, its complexing index (CI) was 2.04-16.93% higher than other LA groups (p < 0.05). The 7.5% LA complex had lower enzyme digestibility (k = 0.065 ± 0.002 min^-1 vs. 0.070-0.072 min^-1 in 5-12.5% LA groups, p < 0.05). And it had 15.88% higher resistance starch (RS) content (44.96 ± 1.25%) compared with native TNS, which was also 2.68-11.06% higher than that of other LA groups (p < 0.05). However, excess LA (>7.5%) led to surface aggregation of unbound fatty acids and weakened structural integrity. Physicochemical analyses showed altered solubility and swelling power (higher than native TNS but gradually decreasing with LA > 2.5%) and modified freeze-thaw stability (increased syneresis): e.g., 85 °C solubility and swelling power: 15.00 ± 0.22%/32.05 ± 0.09% (7.5% LA) vs. 17.61 ± 0.23%/34.50 ± 0.08% (2.5% LA), p < 0.05; syneresis of 7.5% LA group was 25.89 ± 0.15% (p < 0.05). All these physicochemical changes were significantly different from native TNS (p < 0.05), indicating a trade-off between digestion resistance and physicochemical stability. These findings provide a theoretical basis for the utilization of tiger nut starch-lipid complexes as functional ingredients in starch-based systems with tailored digestive properties and bioactive delivery systems.