Process and metabolic engineering for the use of sustainable, renewable, non-food vegetable oils for the production of fuels and chemicals

The refining of vegetable products for food use generates a variety of side streams that are not suitable for human consumption.  Palm Fatty Acid Distillate (PFAD) is one such side stream.  It is rich in fermentable materials, but is a complex mixture and solid at temperatures below 50^oC.  Use of this material in fermentations requires modifications of standard fermentation conditions and of the microorganisms.  Physical considerations include how best to add the material to the fermentation to satisfy mixing, aeration, yield, and mass transfer considerations.  Metabolic Engineering concerns involve manipulating cellular metabolism to balance carbon and energy flow through the TCA cycle and to the intended product pathway.  For example, in an E. coli PFAD fermentation to produce mevalonate, the rate and yield were successfully controlled by manipulating expression of citrate synthase by down-regulating transcription and translation of gltA.   Some additional consideration must be given to the non-metabolizable components of these feedstocks, and appropriate post-fermentation separations and product recovery.