Chitosan-coated zein microcapsules for rumen-protected docosahexaenoic acid delivery and enrichment in goat milk

A zein-chitosan composite microcapsule was developed for rumen-protected DHA delivery. • Microcapsules exhibited high encapsulation efficiency (>90%) and strong structural stability. • In vitro digestion showed 85.76% ruminal passage and > 75% intestinal release. • Compared with algal oil, the DHA conversion rate of milk reached 21.82% after adding microcapsules. Docosahexaenoic acid (DHA) is a long-chain omega-3 polyunsaturated fatty acid with significant nutritional value. Natural DHA-enriched milk is an excellent source, but DHA is lost in the rumen, limiting its enrichment in milk. Herein, a novel zein-chitosan (CS) composite microcapsule system was developed to bypass ruminal degradation and enable controlled post-ruminal DHA release. Zein-CS microcapsules and two zein-only formulations, namely freeze-dried zein microcapsules (Zein-FD) and spray-dried zein microcapsules (Zein-SD), were physically and chemically characterized. Addition of chitosan increased particle size, surface positive charge, and polydispersity index of nanoemulsions. For dried microcapsules, chitosan increased encapsulation efficiency and decreased surface oil. Fourier transform infrared spectroscopy and X-ray diffraction confirmed strong hydrogen bonding, electrostatic, and hydrophobic interactions among zein, chitosan, and DHA. In vitro simulated rumen digestion assays revealed that zein-CS microcapsules achieved a ruminal DHA passage rate of 85.75%, markedly outperforming Zein-FD (34.07–63.70%) and Zein-SD (45.60–58.05%), because chitosan suppressed burst release and premature lipid exposure in the rumen. Total DHA release during simulated stomach and intestinal digestion reached ≥75% for zein-CS capsules. Only Zein-CS preserved alpha-diversity and community structure of rumen microbiota comparable to untreated controls; conversely, oil, Zein-FD, and Zein-SD treatments reduced microbial richness and diversity, and stimulated Lachnospiraceae . Animals fed Zein-CS produced milk containing 10.40 mg/100 mL DHA, higher than goats fed algae oil (3.57 mg/100 mL), with a DHA transfer efficiency of 21.82%. Therefore, Zein-CS microencapsulation effectively shields DHA from ruminal biohydrogenation, preserves rumen microbial homeostasis, enables targeted gastrointestinal release, and enhances milk DHA enrichment.