Supercritical fluid extraction of oil from millet bran

Proso millet bran [Panicum miliaceum (L.)], variety Dakota White, was extracted with supercritical carbon dioxide (SC‐CO2) to yield crude oil. The effects of operating parameters (pressure, temperature, and specific solvent flow) and of features of the raw material (moisture content and particle size) on oil extraction were investigated. Complete de‐oiling of ground millet bran pellets was achieved under 300 bar at 40°C with a specific solvent flow of 2–10 h−1 within 200 to 500 min. Solvent requirements were 20–30 kg CO2/kg raw material. Composition of crude SC‐CO2 oil extracted under optimal conditions, i.e., fatty acid profile, amount of unsaponifiables, tocopherols, free fatty acids, sterols, sterol esters, waxes, hydrocarbons, and phospholipids, was compared to that of crude oil obtained by petroleum ether extraction. These two oils were similar in terms of fatty acid profile and amount of free fatty acids, unsaponifiables, peroxides, and tocopherols. They differed in respect to phospholipids (present in petroleum etherextracted oil and absent in SC‐CO2 extracted oil), metals, and waxes (lower levels in SC‐CO2 extracted oil). The effects of extraction procedures on oxidative stability of crude SC‐CO2 oil were studied. Ensuring that all pieces of the extractor in contact with the oil were in stainless steel; cleaning the separator, i.e., washing with KOH, rinsing, purging with N2 and CO2, and heating; performing a couple of extractions before the main extraction; and achieving the extraction without interruption all positively influenced the oxidative stability of the oil. Conversely, increasing CO2 purity above 99.5% had no effect. Oxidative stability of the SC‐CO2 oil extracted under these conditions was only slightly lower than that of the oil extracted with petroleum ether.