Extraction and purification and microcapsulation of sea buckthorn seed proanthocyanidins using deep eutectic solvent-assisted extraction

This study aimed to develop a green deep eutectic solvents (DES) extraction strategy to recover proanthocyanidins (PAs) from sea buckthorn ( Hippophae rhamnoides ) seeds, a followed by composite biopolymer microencapsulation to overcome the poor stability of PAs. Five choline chloride-based DES systems were screened, and the choline chloride/1,4-butanediol binary DES containing 50% ( v /v) water exhibited the highest extraction efficiency. Single-factor experiments combined with Box–Behnken response surface methodology optimized the extraction parameters: solid-to-liquid ratio of 41:1 mg/mL, extraction temperature of 61 °C, and extraction duration of 3.3 h, delivering a maximum PA yield of 48.025 mg/g seed powder. After purification via D101 macroporous resin, the purity of PA-rich powder reached 69.17%, and LC-MS/MS characterization confirmed the presence of epigallocatechin monomers and dimeric proanthocyanidin B1–B4 in the extract. In vitro antioxidant assays quantified the radical-scavenging capacity of extracted PAs as 4.61 μmol TE/mg (DPPH), 5.53 μmol TE/mg (ABTS) and 6.24 μmol TE/mg (FRAP). To improve thermal and digestive stability, sodium alginate-carboxymethyl cellulose composite microcapsules were fabricated by ionic gelation, achieving an encapsulation efficiency of 89.015%. TGA analysis verified that the composite wall significantly delayed thermal degradation of PAs; in simulated gastric fluid, free PAs reached 53.64% cumulative release after 180 min, while encapsulated PAs only released 21.99%, and the microcapsules exhibited sustained intestinal release up to 45.65% at 180 min. This integrated DES extraction and composite microencapsulation route realizes high-value utilization of sea buckthorn seed waste and provides stable, gastrointestinal-targeted PA ingredients for functional food applications.