Carboxymethyl high-amylose starch and astaxanthin inclusion complex: synthesis, characterization and controlled...

A pH-responsive carboxymethyl high-amylose maize starch (CMHAS, DS = 0.34) was developed as an efficient carrier for astaxanthin (ASTA) encapsulation via coprecipitation. The pH-dependent behavior of CMHAS was confirmed through swelling degree, light transmittance, and zeta potential analyses, demonstrating reversible structural transitions in acidic/neutral environments. Optimized ASTA/CMHAS complexes exhibited a loading capacity of 1.3 mg/g and 32.11 % encapsulation efficiency. Structural characterization revealed the formation of V-type crystalline inclusion complexes (27.4 % crystallinity) via X-ray diffraction, while NMR spectroscopy identified the six-membered ring of ASTA entered the cavity with its center near H-5, while its unembedded long chain remained outside amylose's spiral structure. From results of thermal gravimetric analysis, inclusion complex had the highest retention rates (25.01 %), determining the thermostability of the inclusion complex. Finally, the in vitro gastrointestinal model further confirmed that the inclusion complex exhibited a controlled and sustained-release behavior in 5-125 min (release rate of 45.9 %), but reached 91.3 % in 125-245 min, which protects its antioxidant activity from the destruction of gastric juice.