Fuel alcohol production: effects of free amino nitrogen on fermentation of very-high-gravity wheat mashes

Abstract

Although wheat mashes contain only growth-limiting amounts of free amino nitrogen, fermentations by active dry yeast (Saccharomyces cerevisiae) were completed (all fermentable sugars consumed) in 8 days at 20°C even when the mash contained 35 g of dissolved solids per 100 ml. Supplementing wheat mashes with yeast extract, Casamino Acids, or a single amino acid such as glutamic acid stimulated growth of the yeast and reduced the fermentation time. With 0.9% yeast extract as the supplement, the fermentation time was reduced from 8 to 3 days, and a final ethanol yield of 17.1% (vol/vol) was achieved. Free amino nitrogen derived in situ through the hydrolysis of wheat proteins by a protease could substitute for the exogenous nitrogen source. Studies indicated, however, that exogenously added glycine (although readily taken up by the yeast) reduced the cell yield and prolonged the fermentation time. The results suggested that there are qualitative differences among amino acids with regard to their suitability to serve as nitrogen sources for the growth of yeast. The complete utilization of carbohydrates in wheat mashes containing very little free amino nitrogen presumably resulted because they had the "right" kind of amino acids.

Relationship of Ethanol Yield to Agronomic and Seed Quality Characteristics of Small Grains

“…Ethanol energy balance data must be compiled in more detail to better understand differences between corn and other small grains, such as barley, durum, and wheat. Other grain constituents such as lipids (Murthy et al 2006) and free amino nitrogen (Thomas and Ingledew 1990) influence fermentation efficiencies and need to be explored further. Specifically, high levels of the free amino nitrogen in grain can increase yeast fermentation without having to add an artificial nitrogen source (Thomas and Ingledew 1990).…”

“…Other grain constituents such as lipids (Murthy et al 2006) and free amino nitrogen (Thomas and Ingledew 1990) influence fermentation efficiencies and need to be explored further. Specifically, high levels of the free amino nitrogen in grain can increase yeast fermentation without having to add an artificial nitrogen source (Thomas and Ingledew 1990). Reduced starch lipids may be beneficial in increasing the rate of starch conversion to ethanol and it has been shown that the wheat Hardness locus (Ha) is linked to free polar lipid levels in wheat; soft wheats (Ha) have more polar lipid than hard wheats (ha) (Morrison et al 1989).…”

Evaluation of Waxy Grain Sorghum for Ethanol Production

“…Although yeast itself does not produce exoproteases during the normal fermentation process, addition of proteinases during mashing or the SSF process nevertheless can generate favorable results (increasing the fermentation rate, cell tolerance to ethanol, and final ethanol yield). Hydrolysis of proteins in the raw materials might help with the release of more starch granules from the protein matrix and increase FAN content in the mash (Thomas and Ingledew 1990;Pérez-Carrillo et al 2008), which will facilitate yeast growth and increase the ethanol fermentation rate and efficiency.…”

Germination‐Improved Ethanol Fermentation Performance of High‐Tannin Sorghum in a Laboratory Dry‐Grind Process

“…Germination of sorghum could activate intrinsic enzymes in sorghum seeds, facilitating the breakdown of starch and protein matrices, and resulting in increased levels of monosaccharides, oligosaccharides, and free amino acids. Free amino acids are essential nutrients for yeast growth and are beneficial to ethanol fermentation (Taylor 1983;Thomas and Ingledew 1990;Ratnavathi and Ravi 1991). Using germinated sorghum to produce ethanol may have advantages over the normal process using sorghum meals and could achieve higher ethanol yield and fermentation efficiency because of activated intrinsic enzymes, decreased tannin content, and increased starch digestibility in the germinated sorghum.…”