Quercetin-loaded bioinspired soy protein isolate-zein delivery system enabling pest management and plant growth promotion in sustainable agriculture

Strategies that reduce dependence on synthetic pesticides while maintaining crop productivity are increasingly emphasized in sustainable agriculture. Here, we developed a bioinspired plant protein-based delivery system consisting of quercetin-loaded soy protein isolate (SPI)-zein nanocapsules. Spray drying was employed as a structural engineering strategy to assemble and immobilize nanocapsules into pomegranate-like hierarchical particulate aggregates. SEM, fluorescence spectroscopy, FTIR, UV-vis spectroscopy, XRD and TGA were adopted to characterise quercetin-loaded SPI-zein systems prepared at different SPI:zein ratios. Structural and morphological analyses revealed spherical nanocapsules embedded within interconnected protein aggregates. The formulation with an SPI:zein ratio of 1:2 exhibited the best overall performance, including an encapsulation efficiency of 75.2%, loading capacity of 3.23%, pH-responsive release behaviour, enhanced rainfastness, and improved photochemical and storage stability. Notably, pre-spray-dried nanocapsule dispersions did not significantly improve rainfastness or photoprotection, whereas the spray-dried hierarchical structures exhibited enhanced resistance to wash-off under rainfall conditions, improved protection against UV-induced quercetin photodegradation, and more sustained quercetin release. These findings highlight the functional importance of the engineered pomegranate-like hierarchical architecture. Furthermore, biological assays using pea seedlings (Pisum sativum L.) and black bean aphid (Aphis fabae) demonstrated effective pest deterrence and promotion of plant growth. Our delivery system represents a promising platform for dual-function agrochemical delivery.