Production of free fatty acids using soybean meal carbohydrates as feedstock

Conversion of biomass feedstock to chemicals and fuels has attracted increasing attention recently. Soybean meal, containing significant quantities of carbohydrates, is an inexpensive renewable feedstock. Glucose, galactose and fructose can be obtained by enzymatic hydrolysis of soluble carbohydrates of soybean meal. Free fatty acids (FFAs) are valuable molecules that can be used as precursors for the production of fuels and other value-added chemicals. Two different systems of hydrolysis were examined. In addition, plasmid pRU600 bearing genes involved in raffinose and sucrose metabolism was also transformed into engineered E. coli strains, which allowed more efficient utilization of these two kinds of specific oligosaccharide present in the soybean meal extract. Free fatty acids production were investigated with metabolically engineered E. coli strains carrying the plasmid pXZ18Z (carrying acyl-ACP thioesterase and (3R)-hydroxyacyl-ACP dehydratase (fabZ)) using individual sugars, sugar mixtures and hydrolyzed soybean meal extract. Most engineered strains performed well with individual sugars of glucose, fructose and galactose. However, the triple mutant strain XZK211 (MG1655 fadD^- fabR^- ptsG^-)/pXZ18Z with an additional deletion of ptsG encoding the glucose-specific transporter, functioned the best due to relief of catabolite repression. This strain produced approximately 3.18 g/L of fatty acids with a yield of 0.22 g fatty acids/g total sugar. Maximum free fatty acids production of 2.78 g/L with a high yield of 0.21 g/g was achieved using soybean meal extract hydrolysate. The results suggested that soybean meal carbohydrates could serve as an inexpensive feedstock for the efficient production of free fatty acids.