pH-responsive emulsion gels based on low acyl gellan gum stabilized by yeast protein for enhanced astaxanthin protection.

Astaxanthin (AXT), a powerful natural antioxidant, suffers from limited oral bioavailability owing to its chemical lability and weak water solubility. Microbial-derived biopolymers have received increasing attention for sustainable emulsification in food delivery systems. In this work, highly bioactive AXT was extracted from Haematococcus pluvialis using soybean oil as a green solvent. pH-responsive emulsion gels were fabricated using heat-treated yeast proteins (HYPs) as Pickering stabilizers and low-acyl gellan gum (LAG) as an in situ gelling agent to enhance AXT stabilization. The composite system was characterized by macroscopic/microscopic techniques, and LF-NMR instrument. The effects of LAG concentration and ionic stress (Na+/Ca2+) on stability were investigated, and oral pH responsiveness was validated via in vitro gastrointestinal digestion. It was demonstrated that heat treatment increased the hydrophobicity and interfacial activity of HYPs, leading to strengthened HYPs-LAG interactions and an optimized network structure. The 3% LAG formulation exhibited optimal integrity, droplet size (14.57 ± 11.37 μm), and water-holding capacity. In vitro digestion experiments confirmed that the "gastric protection and intestinal release" behavior effectively improved the bioaccessibility of AXT. Specifically, 3% LAG minimized gastric leakage of AXT, increasing its bioaccessibility from less than 2% to approximately 10%. In a word, a novel carrier integrating green extraction and smart release for oral AXT delivery was presented, thereby providing experimental support for its application in the food and nutraceutical fields.