Preparation and Simulated in Vitro Digestion Study of Gastrodia elata Polysaccharide-Iron Complex

To optimize the preparation process of Gastrodia elata polysaccharide-iron complex (GEP-I), characterize its structure and morphology, and evaluate the iron dissolution and dialysis properties under in vitro simulated gastrointestinal conditions. The effects of reaction time, temperature, and polysaccharide-to-iron ratio on the iron content of GEP-I were investigated using single-factor experiments combined with response surface methodology. The chemical structure and microscopic morphology of GEP-I were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The iron dissolution rate and dialyzability of GEP-I were determined and compared with FeSO₄ using in vitro simulated digestion experiments. The results showed that the optimal preparation conditions were as follows: reaction time of 2.2 h, temperature of 70 °C, and polysaccharide-to-iron ratio of 2:1, under which the iron content reached 23.25%±0.21%. Structural characterization indicated that, compared with Gastrodia elata polysaccharide (GEP), GEP-I exhibited a characteristic Fe-O absorption peak in the FTIR spectrum, and XPS analysis revealed Fe element signals along with changes in coordination-related peaks. SEM imaging showed a smoother and denser surface for GEP-I, confirming the successful preparation of the target product GEP-I. The in vitro digestion experiments demonstrated that GEP-I facilitated a slow release of iron in gastric juice and maintained a high dissolution level in intestinal juice. Upon digestion completion, both the iron dissolution rate (37.64%±0.54%) and dialyzability (54.27%±0.36%) of GEP-I were significantly higher than those of FeSO₄ (7.04%±0.35% and 6.55%±0.33%, respectively; P<0.05). These findings demonstrate that GEP-I possesses favorable iron release and dialyzability, highlighting its potential as a novel iron supplement for applications in the food industry.