Polyphenols from rice husk: A review of emerging extraction techniques and potential applications

Rice husk is a valuable agri-food by-product and an underutilized biomass. Moreover, it constitutes a natural source of antioxidant compounds. Thus, this review compiles data on the total polyphenol content (TPC) in rice husk classified according to pigmentation. In particular, purple husks show high TPC levels (2.15 - 21.90 mg GAE/g) compared to straw (0.69–20.18), straw with a brown line (18.66–20.90), and speckled brown husks (1.08–1.72). In addition, this residue presents specific families of polyphenols like phenolic acids (ferulic, coumaric, caffeic, vanillic, and gallic acid) and flavonoids (quercetin, kaempferol, rutin, catechin, epicatechin, and naringenin). Additionally, conventional and emerging extraction techniques are compared based on their efficiency, solvent consumption reduction, and preservation of functional properties. We also highlight several patent claims focused on the development of rice husk-derived polyphenol products that demonstrate health benefits. Therefore, rice husk is a by-product that is rich in antioxidant compounds and serves as a key driver of sustainable innovations. Its use aligns with the principles of a circular economy, which aim to minimize waste and enhance value throughout the food system.