Stabilization of double emulsions with anthocyanins using a plant protein-inositol hexaphosphate complex.

Background: Double emulsions (water-in-oil-in-water - W/O/W) offer a promising strategy for encapsulating sensitive bioactive compounds like anthocyanins. Their performance depends on the choice of stabilizing agents and the structural integrity of the interfacial layer, particularly under processing conditions such as spray drying. This study combined plant-based proteins (pea and rice) with inositol hexaphosphate (IP6) to investigate their coacervation behavior and effectiveness in stabilizing anthocyanin-loaded double emulsions.

Results: Eight formulations were evaluated, varying in protein type (pea - PP or rice - RP), protein-to-IP6 ratios (1:1 or 2:1), and wall-to-emulsion ratios (2:1 or 4:1). The highest anthocyanin retention (94.4%) was observed in RP-1:1-2:1, and the lowest (30.6%) occurred in RP-2:1-4:1. Scanning electron microscopy (SEM) revealed that higher wall-to-emulsion ratios led to smaller and more uniform microcapsules but retention efficiency decreased. Fourier-transform infrared (FTIR) analysis showed that rice protein systems exhibited higher α-helix content and α-helix:β-sheet ratios, correlating with better film cohesiveness, interfacial integrity, and controlled release. In contrast, pea protein systems were dominated by β-sheet and random coil structures, leading to more disordered matrices, greater surface irregularities, and increased anthocyanin leakage. These structural differences reflect protein-specific interactions with IP6 and are consistent with literature reporting superior mechanical and barrier properties for α-helical structures. Physical characterization showed that pea protein capsules retained more moisture and had higher tapped density, whereas rice protein capsules were lighter in color.

Conclusion: The use of protein-IP6 complexes is a viable strategy for stabilizing anthocyanin-rich double emulsions. Rice protein, due to its α-helical-rich structure, contributes to greater stability and encapsulation efficiency, whereas pea protein provides flexibility and moisture retention but lower structural cohesion. These findings highlight the importance of protein secondary structure in designing efficient plant-based encapsulation systems for food, pharmaceutical, and cosmetic applications. © 2025 Society of Chemical Industry.