Microencapsulation of flaxseed oil using polyphenol-adducted flaxseed protein isolate-flaxseed gum complex coacervates

Abstract

This study aimed to evaluate the applicability of polyphenol-adducted flaxseed protein isolate (FPI)-flaxseed gum (FG) complex coacervates to encapsulate flaxseed oil (FO). FPI was covalently adducted with flaxseed polyphenol (FPP) or hydroxytyrosol (HT). β-sheet was major secondary structure of FPI and its covalent conjugation with polyphenols further increased the β-sheet content. The extent of increase of this ordered structure was found to depend on the type of aducted polyphenol. Subsequently, complex coacervation between polyphenol adducted FPI and FG was studied in terms of optimum complex coacervation pH and protein-to-gum ratio. Compared to FPI and FPI-polyphenol adducts, FPI/FG, (FPI-FPP)/FG and (FPI-HT)/FG complex coacervates had significantly higher random coil and significantly lower β-sheet contents suggesting that these complex coacervates had less ordered structure. Finally, the spray-dried microcapsule powders of FO were produced using FPI/FG, (FPI-FPP)/FG and (FPI-HT)/FG as shell materials. Physicochemical properties of these microcapsules, including surface oil, microencapsulation efficiency and stability against oxidation, were determined. The optimum pH for complex coacervation between FPI/FG, (FPI-FPP)/FG and (FPI-HT)/FG was very close (4.6 ± 0.1) and the optimum protein-to-gum ratio of 6.0 was also identical. All these microcapsules had irregular shape with wrinkled surface morphology. The microcapsules produced using (FPI-HT)/FG complex coacervates had lowest surface oil (1%, w/w) and highest microencapsulation efficiency (95.4%). The microcapsules encapsulated using (FPI-FPP)/FG complex coacervates had the highest stability against oxidation as measured by peroxide value and p-anisidine value. Overall the complex coacervates produced using polyphenol adducted FPI and FG were found to be better than FPI/FG complex coacervates as encapsulating shell materials for oxygen-sensitive oil.