Name: Laith Fareed Al-Obaidi
Date of Degree: DECEMBER, 2012
Title of Study: DEVELOPMENT OF A TWO-STEP EXTRACTION PROCESS FOR WHEAT
GERM OIL RECOVERY
Major Field: Food Science
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 α-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.