Encapsulation of quercetin in pea protein-high methoxyl pectin nanocomplexes: Formation, stability, antioxidant capacity and in vitro release profile

Quercetin (Que) is a popular polyphenol with various activities. However, its application was limited due to its poor water solubility, stability, and low bioavailability. In this study, pea protein isolate (PPI) and high methoxyl pectin (HMP) complexes were fabricated to encapsulate and protect Que. Soluble PPI-HMP complexes at pH 5 and pH 6 were selected based on phase diagram of the two biopolymers during acidification. Fluorescence quenching experiments indicated that complex at pH 5 showed higher binding affinity towards Que than that at pH 6. Complexes at pH 5 displayed considerably higher encapsulation efficiency and loading ability with Que than those at pH 6. XRD results indicated that Que may be transformed from crystalloid to amorphous state after encapsulation. Photochemical and thermal stabilities of Que were improved by complexing with PPI-HMP nanocomplexes at both pH values. Encapsulation improved the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis (2-ethylbenzothiazoline-6-sulfonate) (ABTS) free radical scavenging ability of Que and complex at pH 6 had higher antioxidative ability. The in vitro release study showed that Que displayed initial burst release followed by sustained release in simulated intestinal fluid and higher percentage of Que was released in complex at pH 6 than at pH 5. Data obtained may provide useful information for fabricating pea protein based effective delivery system for Que.