Ultrasound-assisted pectin extraction from 'Lane Late' navel orange: RSM optimization, structural identification and anti-alcoholic liver injury potential.

'Lane Late' (LL) is a late-ripening navel orange consumed in spring and summer. Increased orange production and consumption generate peel waste. To utilize the pectin resource from LL orange peel, this study optimized the ultrasound-assisted extraction of polysaccharides through response surface methodology and characterized the purified fraction (LLLP-1), achieving a crude yield of 12.0% and a pectin isolation yield of 18.4%. LLLP-1 was homogeneous (Mw 53.55 kDa, polydispersity index 1.40), amorphous, low-methyl-esterified and acetylated, with a water solubility of 80 mg/mL at 25 °C. Its HG region consisted of α-D-GalpA (45%, molar ratio), while the RG-I region contained α-L-Araf (26%) and α-D-Galp (21%) residues linked to α-L-Rhap. The RG-II region contained →4)-β-D-Xylp-(1 → (2.3%), →3,4)-β-D-GlcpA-(1 → (1.4%), as well as trace amounts of →4)-β-D-Glcp-(1 → (0.84%), →4)-β-D-Manp-(1 → (0.62%) and L-Fucp (0.42%). LLLP-1 exhibited anti-oxidative and anti-inflammatory activities against alcoholic liver injury. 16S rRNA sequencing revealed enrichment of pectin-degrading bacteria (Bacteroidia and Clostridia) together with beneficial taxa (Akkermansia and Eubacterium coprostanoligenes), alongside suppression of inflammation-associated Helicobacter and Lachnospiraceae UCG001. KEGG pathway prediction suggested regulation of secondary bile acids, carbohydrate and vitamin metabolism, validated by elevated levels of ursodeoxycholic acid, tauroursodeoxycholic acid, pantothenic acid, glucuronic acid, and gut short-chain fatty acids (acetate, propionate, and butyrate). In conclusion, this study provides a foundation for the utilization of LL orange peel as a functional ingredient against alcoholic liver injury.