Abstract
Global demand for renewable and sustainable energy is increasing, and one of the most common biofuels is ethanol. Most ethanol is produced by Saccharomyces cerevisiae (yeast) fermentation of either crops rich in sucrose (e.g., sugar cane and sugar beet) or starch-rich crops (e.g., corn and starchy grains). Ethanol produced from these sources is termed a first-generation biofuel. Yeast fermentation can yield a range of additional valuable co-products that accumulate during primary fermentation (e.g., protein concentrates, water soluble metabolites, fusel alcohols, and industrial enzymes). Distillers’ solubles is a liquid co-product that can be used in animal feed or as a resource for recovery of valuable materials. In some processes it is preferred that this fraction is modified by a second fermentation with another fermentation organism (e.g., lactic acid bacteria). Such two stage fermentations can produce valuable compounds, such as 1,3-propanediol, organic acids, and bacteriocins. The use of lactic acid bacteria can also lead to the aggregation of stillage proteins and enable protein aggregation into concentrates. Once concentrated, the protein has utility as a high-protein feed ingredient. After separation of protein concentrates the remaining solution is a potential source of several known small molecules. The purpose of this review is to provide policy makers, bioethanol producers, and researchers insight into additional added-value products that can be recovered from ethanol beers. Novel products may be isolated during or after distillation. The ability to isolate and purify these compounds can provide substantial additional revenue for biofuel manufacturers through the development of marketable co-products.
Highlights
The demand for fuel ethanol continues to grow, with global production projected to surpass 140 billion litres/year [1]
This review will examine several valuable co-products that accumulate during alcoholic fermentation (α-glycerylphosphorylcholine, and fusel alcohols), followed by those produced during secondary fermentation of the distillers’ grain co-products, which are primarily from first generation ethanol production
These organic acids canafter inhibit fermentation primary ethanolic fermentation, the resulting thin stillage by-product can be used as culture example, acetic acid present in commercial Saccharomyces cerevisiae fermentations media for lactic acid bacteria (LAB) fermentation sirable, with concentrations > 0.4 g/L signifying bacterial contamination and co for producing additional succinic acid, lactic acid, and acetic acid [14,15]
Summary
The demand for fuel ethanol continues to grow, with global production projected to surpass 140 billion litres/year [1]. The most common yeast used in alcoholic fermentation, Saccharomyces cerevisiae, is preferred for rapid and efficient conversion of sugar solutions to solutions with correspondingly high ethanol concentrations The latter solutions are readily distilled and dehydrated to yield products suitable for blending with gasoline. Upon the completion of ethanolic fermentation, the distillers’ grain waste by-product can be further upgraded and enriched (e.g., secondary fermentation) to produce additional added-value compounds (e.g., 1,3-propanediol), as well as a highly concentrated protein that can be utilized as feed for domestic animals [14,15]. This review will examine several valuable co-products that accumulate during alcoholic fermentation (α-glycerylphosphorylcholine, and fusel alcohols), followed by those produced during secondary fermentation (e.g., organic acids) of the distillers’ grain co-products (whole and thin stillage), which are primarily from first generation ethanol production. The recovery and purification of these compounds can further add value and provide opportunities for increased utilization of grain crops and provide ethanol producers access to new markets
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