Effects of combining ultrasound and dual enzymolysis with hydroxypropylation, acrylate grafting, or phosphate grafting on the physicochemical and functional properties of oil palm mesocarp expeller dietary fiber

Oil palm mesocarp expeller is an abundant and low-cost dietary fiber resource, but its poor hydration and adsorption properties limit its utilization in foods. Therefore, ultrasound and enzymolysis combined with hydroxypropylation, acrylate grafting, or phosphate grafting were used to improve the adsorption properties of oil palm mesocarp expeller fiber (OPMEDF) for the first time. The results revealed that these composite modifications made the microstructure of OPMEDF more porous, and significantly increased its soluble fiber content, surface area, hydration properties, and sorption abilities of glucose, nitrite, copper, and lead ions but decreased its brightness. OPMEDF modified by ultrasound, enzymolysis, and acrylate grafting had the highest content of extractable polyphenol and sorption abilities on oil and nitrite ion. OPMEDF subjected to ultrasound, enzymolysis, and phosphate grafting showed the highest water-swelling volume (3.84 mL g⁻¹) and sorption abilities of copper (II) and lead (II) ions. Notably, OPMEDF modified by ultrasound, enzymolysis, and hydroxypropylation exhibited the highest soluble fiber content (14.72 g∙100 g⁻¹), water-retention ability (5.22 g g⁻¹), viscosity (13.90 cp), and glucose adsorption capacity (38.18 g∙100 g⁻¹). These results indicated that these composite modifications are good options to improve the adsorption capacities of OPMEDF and can expand its potential hypoglycemic and hypolipidemic effects.