Coprocessing corn germ meal for oil recovery and ethanol production: a process model for lipid-producing energy crops

Authors: JIA, YUYAO - University Of Illinois; KUMAR, DEEPAK - University Of Illinois; Moser, Jill; Dien, Bruce; RAUSCH, KENT - University Of Illinois; TUMBLESON, M - University Of Illinois; SINGH, VIJAY - University Of Illinois

Submitted to: Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2022
Publication Date: 3/29/2022
Citation: Jia, Y., Kumar, D., Winkler-Moser, J.K., Dien, B.S., Rausch, K., Tumbleson, M.E., Singh, V. 2022. Coprocessing corn germ meal for oil recovery and ethanol production: a process model for lipid-producing energy crops. Processes. 10(4). Article 661. https://doi.org/10.3390/pr10040661.
DOI: https://doi.org/10.3390/pr10040661

Interpretive Summary: Warm season grasses are the most productive plants in the world for generating above ground biomass (e.g. amount of leaves, stems, and seeds). The stems and leaves can be converted to sugars for fermentation to renewable fuels and chemicals. However, processes developed in the lab have resisted commercialization because of the thin profit margins and high capital requirements. ARS researchers are working with a national research consortium that is engineering grasses to accumulate vegetable oil in their stems and leaves. The grasses would be harvested, and the oil recovered while the residual fibers are converted to sugars for fermentation. The oil would generate new revenue when sold either to make jet fuel, green diesel, or for chemicals. However, new technology is required to recover the oil and at the same time preparing the fibers for conversion to sugars. Because the lipid-containing plants are still in development, this study used corn germ meal (a corn wet milling coproduct). The corn germ meal was treated under conditions that are favorable for oil recovery and pre-treatment of the fibers to allow for simultaneous release of sugars using enzymes, and conversion of sugars to ethanol using yeast fermentation. Under these conditions, it was shown that the oil was recovered at good yields and improved the yield of sugars and overall ethanol yield. However, the lipid profile appeared to be detrimentally affected, indicating that it may be better to extract the oil prior to converting the fibers to sugars and fuel. This is of interest to farmers looking to the future for new crops and large agricultural processors interested in new resources for making sustainable fuels.

Technical Abstract: Efforts to engineer high-productivity crops to accumulate oils in their vegetative tissue present the possibility of expanding biodiesel production. However, processing the new crops for lipid recovery and ethanol production from cell wall saccharides is challenging and expensive. In a previous study using corn germ meal as a model substrate, we reported that liquid hot water (LHW) pretreatment enriched the lipid concentration by 2.2 to 4.2 fold. This study investigated combining oil recovery with ethanol production by extracting oil following LHW and simultaneous saccharification and co-fermentation (SSCF) of the biomass. Corn germ meal was again used to model the oil-bearing energy crops. Pretreated germ meal hydrolysate or solids (160 and 180 °C for 10 min) were fermented, and lipids were extracted from both the spent fermentation whole broth and fermentation solids, which were recovered by centrifugation and convective drying. Lipid contents in spent fermentation solids increased 3.7 to 5.7 fold compared to the beginning germ meal. The highest lipid yield achieved after fermentation was 36.0 mg lipid g-1 raw biomass; the maximum relative amount of triacylglycerol (TAG) was 50.9% of extracted oil. Although the fermentation step increased the lipid concentration of the recovered solids, it did not improve the lipid yields of pretreated biomass and detrimentally affected oil compositions by increasing the relative concentrations of free fatty acids.