CO2 assisted mechanical expression of fat from rendered materials

•Poultry meal fat content can be reduced from 12.1% to 2.3% (81%) with CO2 enhanced mechanical expression with 172 bar of CO2, Peff of 600 bar and a temperature of 40 °C.•These conditions are achievable in a commercial continuous press.•CO2 pressurization prior to mechanical pressure is required for maximum enhancement.•CO2 pretreatment of RM before pressing may be a viable option for enhanced expression on an industrial scale.•CO2 induced viscosity reduction and matrix rupture due to CO2 dissolving into the fat are both contributing mechanisms to expression enhancement.

This work employs liquid and supercritical carbon dioxide for the enhanced expression of fat from rendered materials, specifically a finished poultry meal. Current industrial rendering processes use continuous screw presses or expellers to remove fats from rendered materials; however, this process can leave 10 to 15% residual fat. The higher economic value for the fat and emerging markets for low fat rendered protein meals makes enhanced fat recovery desirable. Results from this work demonstrate the use of CO2 assisted mechanical expression where the rendered material is pressed in the presence of pressurized CO2. The fat content of the poultry meal was reduced from an initial 12.1% down to 2.3% after pressing. The optimal conditions for a maximum expression were on the order of 40 °C, 210 bar of CO2, and 500 bar of effective mechanical pressure. An optimum effective mechanical pressure was observed at around 500 bar, which can be attributed to a reduced permeability of the CO2–fat mixture through the protein matrix at high mechanical pressures, as described by Darcy's law. At CO2 pressures greater than 172 bar, expression enhancement is negligible, likely due to a plateau reached for the viscosity of the oil–CO2 mixture beyond such pressure. The primary mechanisms governing the enhanced expression were the reduced viscosity of the fat with CO2 dissolution; which increases the drainage of fat through the cake, and the confinement rupture due to swelling upon CO2 dissolution. Overall, it was demonstrated that high expression yields can be achieved when conducting a gas-assisted mechanical expression of rendered materials, using only a fraction of the amount of CO2 used for CO2-only extractions. Furthermore, the optimum operating conditions are suitable for application in screw presses or expellers currently used on industrial scales.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide