Rapeseed protein refining using 1,2-propanediol and natural deep eutectic solvents

Natural Deep Eutectic Solvents (NADES) represent a novel class of food grade and non-toxic solvents that have a high solubilization capacity for phenolic compounds. The objective of this study was to investigate the kinetics of the selective extraction of total polyphenols, phytate, and glucosinolates from dehulled rapeseed. The aim was to improve both, the sensory and nutritional properties by maximizing the reduction of off-taste, off-flavor, color, and antinutrients of dehulled rapeseed.

NADES was prepared from food grade chemicals, choline chloride and 1,2-propanediol (ChChPro_13) or betaine and 1,2-propanediol (BetaPro_14). Extractions using aqueous 1,2-propanediol, aqueous ethanol, and water were used as a reference. A bicinchoninic acid test was used for both the quantification of proteins and polyphenols in extracts from batch extraction. Phytic acid and glucosinolates were determined using a colorimetric test and HPLC, respectively. A three-stage percolation column sequential extraction was investigated for scale-up using the same analytical methods.

NADES extraction yields of total polyphenolic compounds as compared to aqueous 1,2-propanediol or ethanol were significantly higher (α > 0.05). The extraction rate constant of polyphenols increased with increasing water content in both NADES and 1,2-propanediol. ChChPro_13 and BetaPro_14 yielded extraction yields of total polyphenols of up to 670 mg L^-1 while 1,2-propanediol yielded up to 550 mg L^-1 at a 1:10 solids-to-liquid ratio. Protein solubility was highest in water and increased in NADES and 1,2-propanediol with increasing water content. The extraction efficiency of phytate and glucosinolates in NADES increased to around 240 mg L^-1 phytate and 0.3 mg L^-1 glucosinolates at 20% water content. Pure water extracted 1,323 mg L^-1 and 2 mg L^-1 phytate and glucosinolates, respectively. The pilot-scale column extraction data showed similar trends and allowed to refine more material while reducing solvent and water consumption.