Fermentative processes of producing organic compounds from saccharides are widely used, and products obtained by the processes are used as various industrial raw materials.
Saccharides which are currently used as raw materials for the fermentative production processes and chemical conversion processes are saccharides derived from edible materials such as sugar cane, starch, sugar beet, corn, potatoes, cassava and sugar maple.
However, regarding the saccharides derived from edible materials, there are concerns that the prices of edible materials will soar as the world population increases and that edible materials will be in short supply due to bad weather or climate change. Also, use of edible materials for industrial raw materials, which is in competition with food use when food supply falls short, faces ethical criticism and concerns. Thus, development of a process of efficiently producing a saccharide solution from a non-edible material, a saccharide with lower purity containing impurities or the like or development of a process of efficiently converting the saccharide solution obtained as a raw material for the fermentative production into an industrial raw material is a task that should be accomplished in the future.
Methods for obtaining a saccharide solution from a non-edible material include a method in which cellulose and hemicellulose contained in a non-edible material are hydrolyzed into monosaccharides, for example hexoses such as glucose or pentoses such as xylose, using concentrated sulfuric acid (PTL 1), a method in which a non-edible material is subjected to pretreatment to improve the reactivity and then hydrolyzed through enzyme reaction (PTL 2), a hydrolysis method using subcritical or supercritical water or the like.
When these methods are used, however, cellulose and hemicellulose contained in a non-edible material are hydrolyzed to produce saccharides such as glucose and xylose, and degradation of the saccharides advances at the same time. The degradation of the saccharides generates carbonyl compounds as by-products apart from the saccharides. Specifically for example, carbonyl compounds such as aldehyde compounds, e.g. furfural, hydroxymethylfurfural, glycolaldehyde, syringaldehyde and formic acid, and ketone compounds, e.g. dihydroxyacetone and benzoquinone, are generated.
Of the carbonyl compounds apart from the saccharides, an aldehyde compound such as furfural and hydroxymethylfurfural and the like have the property of inhibiting the reaction in fermentative production processes using microorganisms. Specifically, an aldehyde compound and the like inhibit the multiplication of microorganisms or inhibit the fermentative production and thus decrease the yield of the fermentative production. Therefore, these compounds are called fermentation inhibitors and cause a large problem when a saccharide solution obtained from a non-edible material is used as a raw material for fermentation.
To solve this problem, methods for removing a fermentation inhibitor generated such as furfural have been studied, and for example, methods for removing a fermentation inhibitor through adsorption using various adsorbents such as active carbon and the like have been proposed (for example, PTL 3 and NPL 1). However, it is difficult to remove only the fermentation inhibitor selectively by the methods by adsorption, and drawbacks of the methods are that the saccharide concentration decreases because the saccharide is adsorbed and that these methods require costs for production and regeneration of the adsorbent. As other methods for removing a fermentation inhibitor, removal methods through reduction using a reducing agent such as sodium hyposulfite (NPLs 2 to 4 and PTL 4), removal methods using a synthetic resin (PTL 5) and the like have been proposed.