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Development of a two-step extraction process for wheat germ oil recovery

Al-Obaidi, Laith Fareed
Scope and Method of Study: The main objective of this study was to optimize the mechanical extraction process parameters (cage temperature, germ pretreatment, shaft speed, back pressure and shaft arrangement) to increase wheat germ oil (WGO) yield without compromising oil quality. A two-step process: pre-pressing of wheat germ using a screw press followed by extraction of residual oil from the pressed cake by aqueous and aqueous enzymatic extraction techniques was also examined. In addition, mechanically extracted WGO quality was compared to that of hexane and supercritical CO2 extracted oil by analyzing the free fatty acid (FFA), peroxide value (PV), p- anisidine value (AV), water content, phosphorus, tocopherols and phospholipids content.
Finding and Conclusion: The highest oil yield from the screw press, about 47.7%, was obtained under the following conditions: severe shaft arrangement, cage temperature of 107 oC, germ pretreatment at 82 oC, high back pressure, and shaft speed at 400 rpm. The aqueous extraction of wheat germ (WG) cake with boric acid-NaOH (pH 8) buffer using fine particle size at liquid solid ratio (LSR) of 20 and extraction time of 0.5 h resulted in the highest oil yield, 79.64%. The enzymatic extraction of WG cake with Alcalase 2.4L FG at LSR of 16.5, enzyme concentration of 4%, and extraction time of 5.25 h resulted in 76.7% oil yield which was slightly lower than the aqueous extraction. Mechanically extracted oil had better quality (lower FFA, PV, and AV values and higher a-tocopherol content) than that of the commercially hexane-extracted oil. A two-step process involving mechanical pressing of full fat WG followed by aqueous extraction of the residual cake from the mechanical press would result in 90% WGO recovery. This process can be an environmentally benign alternative to hexane extraction.