Structure-function relationships of pectic Fibers from pitaya Peel in astaxanthin-loaded emulsion systems

Two kinds of dietary fiber, designated acid-soluble dietary fiber (ADF) and alkali-soluble dietary fiber (ASF), were sequentially extracted from pitaya peel. The galacturonic acid contents of ADF and ASF were 79.79% and 80.40%, respectively. The droplet size of ADF-stabilized emulsion (1.24 μm) was higher than that of ASF-stabilized emulsion (0.88 μm). After 7 days of storage, the astaxanthin (AST) retention rate in ADF-stabilized emulsion (66.4%) and ASF-stabilized emulsion (62.8%) were both higher than that of free AST (30.6%). Following 8 h of UV irradiation, the AST retention rate in ADF-stabilized emulsions (56.4%) was significantly higher than that in ASF-stabilized emulsions (41.4%). During simulated gastrointestinal digestion, the bioaccessibility of AST in ADF-stabilized emulsions reached 55.4%, compared with 46.5% for ASF-stabilized emulsions and 22.8% for free AST. In conclusion, both ADF and ASF provide effective protection for AST during storage, UV exposure, and digestion, highlighting their potential as food-grade emulsifiers.