Isolation of Acidic Mucilage from the Outer Seed Coat of Shaddock (Citrus grandis Osbeck) and Evaluation of Its Functional Properties

After water imbibition, the outer layer seed coat of shaddock (Citrus grandis Osbeck) produces transparent gel-like mucilage (MSS), but its characteristics have never been studied before. This study aimed to assess the physico-chemical and functional properties of MSS. Extractions of MSS with deionized water at room temperature yielded about 3.5% based on the dry weight of seed. The major components were neutral sugars and uronic acids in the amounts of 33.5% and 49.6%, respectively. The acidic nature of MSS was confirmed by ruthenium red staining. Its water holding capacity and viscosity were 44.53 g•g-1 DW and 1660 cP at 10 g/L, respectively. MSS showed a weak quenching activity against DPPH radical, and moderate ferrous ion-chelating and superoxide anion radical scavenging activities, with IC50 value of 1.5 g/L and 1.1 g/L, respectively. A methyl thiazolyl tetrazolium (MTT) assay demonstrated that MSS significantly stimulated the viability of mouse skin fibroblasts (NIH/3T3) at 5 - 300 mg/L. These results impart the potential usefulness of the MSS to food, cosmetics and other applications.