Rapeseed Refined: Extraction of Polyphenols, Glucosinolates, Phytate, and Protein from Whole Dehulled Rapeseed Using Natural Deep Eutectic Solvents

Natural deep eutectic solvents (NADES) have been shown to provide excellent extraction capabilities for phenolic compounds from plant materials. In this study, we investigated the kinetics and efficiency of choline chloride- and betaine-1,2-propanediol-based NADES to extract phenolic compounds, glucosinolates, phytate, and proteins from whole dehulled rapeseed kernels. These NADES were compared to 1,2-propanediol, water, and 60% aqueous ethanol. Solvent temperature (55 °C) and solid-to-liquid ratio (1:10 w/w) were kept constant. The extraction rate constant for phenolic compounds and glucosinolates increased more than ten times with increasing water content in the range of 10–40% w/w in NADES or 1,2-propanediol. Choline chloride-based NADES extracted the highest amounts of total phenolic compounds, up to 6.79 g kg^–1, while betaine-based NADES extracted the highest amounts of glucosinolates, up to 3.48 g kg^–1. Phytate solubility increased with increasing water content in NADES and 1,2-propanediol. Protein extraction also increased with an increasing water content but followed slower kinetics than the extraction of phenolic compounds. Limiting solvent water content and extraction duration will help exploit differences between the analytes’ extraction kinetics, ensuring low protein coextraction. The extracted rapeseed could be further processed to recover purified, white, and plain-tasting oleosomes, rapeseed protein, and fiber.