Protein-Polysaccharide Complexes as Delivery Systems for Quercetin: Mechanisms, Microstructure, and Applications in High-Protein Beverages

Abstract

Quercetin is a dietary flavonol, which has been reported with antioxidants, anti-inflammatory and anti-cancer properties. In food application, its use is limited due to low aqueous solubility, susceptibility to thermal degradation and low bioavailability. To overcome these limitations, protein-polysaccharide complexes are a biocompatible, biodegradable and edible solution. This review summarises the available literature in this field but provides new information regarding the application of protein-polysaccharide complex to deliver quercetin in a new environment (high protein beverages) with physicochemical and sensory issues. Another significant contribution of this review is that it incorporates recent developments and highlights the need to translate molecular-level mechanisms of complex formation from bench research to food and nutrition innovation. Specifically, this review examines and systematically analyse the mechanisms for noncovalent complexation due to electrostatic, hydrogen bonding, and hydrophobic interactions, as well as covalent interactions (Maillard reactions, carbodiimide cross-linking and enzymatic complexation) and correlate these interactions with advanced microstructural characterisation methods on a molecular level. Thereafter, the review discusses how these interactions affect measurable functional properties such as encapsulation efficiency, loading capacity, stability, and bioavailability enhancement. Moreover, it compares various delivery architectures like nanoemulsions, Pickering emulsions, HIPEs and stimuli-responsive hydrogels to both technical and sensory constraints of high-protein beverages and contrasts their behaviours, particularly when using whey protein, and other polysaccharides. Finally, a detailed discussion of the barriers to scale up, batch consistency, cost-effectiveness and regulatory aspects of the industry and a summary of the emerging research areas such as advanced cross linking, personalised and stimuli responsive systems, sustainable green processing and clinical translation. Overall, this review shows that protein-polysaccharide complexes have great importance at the functional ingredient delivery and commercial beverage formulation interface. Thus, it proposes an innovation strategy that advances both scientific understanding and practical application.