Starch crops, fermentation

Feedstock Options. Ethanol may be produced via fermentation (with yeast) of 6-carbon or 12-carbon sugars from a number of carbohydrate sources including sugar crops, starch crops, or lignocellulosic materials. 

Most current commercial ethanol production is from the fermentation of sugar and starch crops. Yeast can rapidly convert sucrose to ethanol with a theoretical carbon conversion of 67%. The production of ethanol from corn grew to about 1.9 billion gallons in 2001. This accounted for 90% of the total ethanol production and an estimated 615 million bushels of corn (6.2% of total corn produced) were consumed. The remaining 10% of ethanol production was by fermentation of grain sorghum, barley, wheat, cheese whey, and potatoes. 

Both starch crops and lignocellulosics contain polymers of sugars that can be broken down into monomers and used in fermentation. The federally-subsidized production of fuel ethanol from com is an example of bioconversion that takes advantage of well-established wet and dry milling techniques after which the starch is enzymatically converted to glucose for yeast fermentation. 

In this chapter we describe the use of pea seeds to express the bacterial enzyme a-amylase. Bacterial exoenzymes like the heat stable a-amylase from Bacillus licheni-formis are important for starch hydrolysis in the food industry. The enzymatic properties of a-amylase are well understood [13,14], it is one of the most thermostable enzymes in nature and it is the most commonly used enzyme in biotechnological processes. Although fermentation in bacteria allows highly efficient enzyme production, plant-based synthesis allows in situ enzymatic activity to degrade endogenous reserve starch, as shown in experiments with non-crop plants performed under greenhouse conditions [12,15]. Finally, the quantitative and sensitive detection of a-amylase activ-... 

The term energy crop can be used both for biomass crops that simply provide high output of biomass per hectare for low inputs, and for those that provide specific products that can be converted into other biofuels such as sugar or starch for bioethanol by fermentation, or into vegetable oil for biodiesel by transesterificatiou... 

Other applications for PGRs include the enhancement of crop establishment through the promotion of roots from cuttings, the prevention of sprouting in storage potatoes and the stimulation of germination and hence of starch hydrolysis in malting barley prior to fermentation. 

Polylactide is a degradable polyester, formed by the ring-opening polymerization of lactide or the condensation polymerization of lactic acid. Lactide is produced from lactic acid, which derives from the fermentation of D-glucose, which is usually harvested from high-starch-content crops, such as com or sugar beet (Fig. 1). 

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