Curcumin-loaded microcapsules with soy and whey protein as wall material: In vitro release, and ex vivo absorption based on the rat small intestine

Plant proteins, serving as an environmentally friendly and cost-effective alternative to animal proteins, have gained widespread usage in encapsulating various bioactive compounds like curcumin. However, understanding how plant protein-based microcapsules compare to those made with animal proteins in terms of disintegration, release, and absorption in the gastrointestinal tract (GIT) remains limited. This study aims to investigate the impact of soy protein isolate (SPI) and whey protein isolate (WPI) as wall materials on the release, stability, and absorption of curcumin. Spray-dried SPI-based microcapsules (SPI–C) exhibited significantly lower encapsulation efficiency (77.1%) and loading efficiency (3.6%) compared to WPI-based microcapsules (WPI–C) (97.6% and 9.6%, respectively). Structural analysis revealed pleated hollow spherical structures for SPI-C and a concave surface with a single-chamber structure for WPI-C. SPI-C demonstrated higher proteolysis (55.8% vs . 44.1%) during in vitro digestion, leading to greater curcumin release ratio (67.9% vs . 59.2%) and digestive stability (97.9% vs . 93.7%) compared to WPI-C. Notably, SPI-C exhibited higher apparent permeability (0.97 × 10 −6  cm/s) to the ex vivo rat small intestine than WPI-C (0.44 × 10 −6  cm/s). These findings suggest improved gastrointestinal stability and absorption of curcumin encapsulated by SPI, indicating the potential for enhanced utilization of plant-derived proteins in encapsulating bioactive compounds.