Corn endosperm fermentation using endogenous amino nitrogen generated by a fungal protease

Fractionating the corn kernel to separate endosperm from germ and pericarp improves corn ethanol processing by increasing fermentation throughput and generating salable coproducts. One fractionation technology, dry fractionation (DF), suffers from loss of germ-derived nutrients and amino acids, resulting in poor fermentation performance. Such deficiencies may be addressed by increasing nitrogen and other nutritional supplementation. As an alternative to exogenous nitrogen source, we investigated the use of a fungal protease to generate free amino nitrogen (FAN) from corn endosperm. Incubation of endosperm with protease did not affect subsequent liquefaction and saccharification. FAN supplementation through proteolysis resulted in fermentation being 99% complete in 48 hr, compared to 93% maximum with urea supplementation. Viable cell growth rates were similar in FAN and urea-supplemented fermentations. Urea and FAN addition resulted in similar fermentation characteristics and similar FAN consumption rates as with FAN alone, which was indicative that FAN was assimilated preferentially. Increased amounts of maltose remaining after fermentation were correlated with initial FAN concentrations in mash. This observed trend was implicated in ethanol yield reduction of 2 g/L at high protease loading (generating 1.6 mg of FAN/g of glucose substrate) compared to a urea control. Using a glucose and maltose solution, we confirmed higher residual maltose in fermentations supplemented with high FAN concentrations. Use of protease to generate optimal FAN concentration in mash (1.2 mg of FAN/g of glucose substrate) could improve economics of dry fractionated corn ethanol production by increasing fermentation rates and, consequently, reducing fermentation time.