Gas assisted mechanical expression of cocoa butter from cocoa nibs and edible oils from oilseeds

Abstract

The current methods used to recover high quality oil from oilseeds have low yields (mechanical expression, aqueous extraction), require the use of toxic chemicals and rigorous purification processes that can reduce the quality of the oil (solvent extraction with hexane) or are unsuitable for the recovery of commodity oils due to the low solubility of plant oils in environmentally benign solvents (supercritical extraction with CO 2). Gas assisted mechanical expression (GAME) utilises the much higher solubility of supercritical CO 2 in the oil to enhance the extraction yields of mechanical expression. GAME experiments with cocoa nibs were performed at 40–100 °C, CO 2 pressures of 0–20 MPa and effective mechanical pressures of 20–50 MPa. The maximum yield with conventional expression (71.8%) was obtained at a mechanical pressure of 50 MPa and a temperature of 100 °C. It is shown that GAME has a substantially higher yield than conventional mechanical expression for the recovery of cocoa butter from cocoa nibs, with the highest yield (87.1%) obtained at 100 °C, a CO 2 pressure of 10 MPa and an effective mechanical pressure of 50 MPa. The cocoa butter yield increases with increasing CO 2 pressure until 10 MPa but remains almost constant for higher CO 2 pressures. In contrast to conventional expression GAME also allows the recovery of cocoa butter from cocoa nibs at temperatures below the melting point of pure cocoa butter. The cocoa butter produced with GAME was found to be unfractionated and is therefore of the same quality as mechanically expressed cocoa butter. Experiments with linseed and sesame seed show that GAME performed at 40 °C with 10 MPa CO 2 also results in an increased yield of oil (71.8–83.8% for linseed, 74.3–80.2% for sesame seed) when compared to the yield obtained with conventional mechanical expression performed at 40 °C (38.5–45.7% for linseed, 60.1–65.6% for sesame seed). From these results it is concluded that GAME offers a promising process for the recovery of high-quality vegetable oils at high yields.