Encapsulation of a PUFA-rich oil in alginate-protein hydrogels

Njangsa seed oil (NSO), valued for its high polyunsaturated fatty acid (PUFA) content and bioactive properties, is highly susceptible to oxidation. This study aimed to enhance its oxidative stability and controlled delivery through encapsulation, optimized using a three-factor-five-level central composite design to assess the effects of alginate (1.5–2.5 g/dL) and protein (3–6 g/dL) concentrations, and NSO load (3–6 mL/dL) on encapsulation efficiency (EE). Optimal formulations using alginate (2.5, 2.5, and 2.8 g/dL) with Bambara grondnut protein isolate (3 g/dL) (ALG-BPI), Bambara groundnut protein concentrate (5 g/dL) (ALG-BPC) and soy protein isolate (7 g/dL) (ALG-SPI) carriers, and 6, 6, and 8.25 mL/dL NSO load, achieved EE values of 88.08, 87.21, and 84.30 %, with average sizes of 1.98, 2.38, and 1.70 mm, and sphericity factors of 0.04, 0.047, and 0.06, respectively. Fatty acid composition remained unchanged post-encapsulation. Confocal and scanning electron microscopy showed uniform oil distribution and a highly porous internal structure, particularly in ALG-BPI-NSO. FTIR analysis confirmed successful encapsulation. Among the three formulations, ALG-SPI-NSO exhibited delayed NSO release, and retained higher total phenolic content (2.05 mg/g), and antioxidant activity (63.03 % DPPH, 34.29 % ABTS) during simulated gastric digestion. However, ALG-BPI-NSO demonstrated superior oxidative stability, as indicated by a higher onset temperature (252 °C) linked to effective retention within the hydrogel and higher emulsifying property of BPI. Our findings suggest that the three formulations, particularly ALG-SPI-NSO and ALG-BPI-NSO, are promising for food and nutraceutical applications due to their enhanced stability and preservation of phenolic and antioxidant properties of NSO. • NSO encapsulation was optimized using CCD. • Properties of NSO hydrogels was influenced by polymer type and concentration. • Predicted encapsulation efficiency was close to experimental values, reaching >84 %. • Protein inclusion in the wall material enhanced hydrogels' key characteristics. • PDSC showed improved oxidative stability of encapsulated NSO. • Similar amount of fatty acids were determined in both free NSO and hydrogels.