Influence of starch type and inulin on the physical stability and structural changes of enteral food formulations during gastrointestinal digestion

The performance of enteral formulations depends on the organization and interactions among their components, which may also influence structural changes during gastrointestinal digestion. Starches with different amylose/amylopectin ratios and soluble fibers such as inulin may affect physical stability and digestive behavior. This study evaluated how starch type and inulin affect the physical stability of enteral food formulations and investigated digestion-induced structural changes in a selected regular-starch formulation with and without inulin during simulated gastrointestinal digestion. Twenty formulations containing soy protein, flaxseed oil, gum arabic, and different corn starches were developed. Commercial corn starch (Maizena®, Unilever, Brazil), regular corn starch (Amisol® 3408), high-amylose starch (Hylon VII®), and high-amylopectin starch (Amisol® 4000) (Ingredion, Brazil) were evaluated with 0–6% (w/w) inulin (Beneo/Univar Solutions, São Paulo, Brazil). After preliminary screening, four formulations containing 4% inulin, one for each starch type, were selected and evaluated during 7 days of storage by phase separation, pH, instrumental color, laser-diffraction particle size distribution, and optical microscopy. The regular-starch formulation, with and without inulin, was subjected to static in vitro gastrointestinal digestion and particle size distributions (D10, D50, and D90) were evaluated after gastric and intestinal phases. Starch type influenced physical stability. The regular-starch formulation containing 4% inulin showed the lowest phase separation (5.3 ± 1.9% after 7 days versus 8.7–16.6% for the other starches). Across the selected formulations, pH ranged from 5.74 to 6.12. Color parameters ranged from 73.16 to 76.00 for L* (lightness), −1.11 to −0.72 for a* (green–red axis), and 28.31 to 31.05 for b* (blue–yellow axis), with variations in a* among formulations and throughout storage, while b* showed a decrease over time. During storage, the regular-starch formulation showed small changes in D50, from 26.44–26.56 µm at day 0 to 21.77–24.38 µm at day 7, whereas D90 increased from 111.81–152.65 to 228.67–279.24 µm. Optical microscopy indicated changes in matrix organization. During gastric digestion, D50 values were similar with (25.96–26.31 µm) and without inulin (27.21–28.08 µm), whereas D90 was lower with inulin (41.91–42.15 µm) than without inulin (137.67–278.77 µm), revealing distinct distributions. After intestinal digestion, D50 ranged from 57.52–177.08 µm with inulin and 74.59–121.93 µm without inulin, while D90 reached 345.85–394.36 and 286.44–439.47 µm, respectively. The limited change in D50 during the gastric phase may reflect the absence of amylase, whereas pancreatin during the intestinal phase promoted greater matrix restructuring. Starch type and inulin influenced the physical stability of enteral matrices, with regular corn starch combined with 4% inulin showing the best technological performance. Gastrointestinal digestion altered particle size distributions, highlighting the importance of evaluating the complete distribution rather than isolated median values.

Acknowledgments: FAPESP (Process 2026/03052-1).