Biomass carbohydrate source

Biomass carbohydrates, which represent the most abundant renewable sources available, are currently viewed as a feedstock for the green chemistry of the future [267-269]. 

Major biotechnological uses of the biomass carbohydrate moiety have attracted worldwide attention. Controlled cellulose degradation by cellulases may produce materials for important multifarious applications carbohydrates that can be used in the food and beverage industries, cellulose microfibril fragments for non-caloric food additives, hyperabsorbent cellulose fibers from fragmented cellulose microfibrils which can be used in biomedical, commercial and house-hold absorbent materials. Biomass-derived glucose syrups can also be used as carbon source in industrial fermentations for the production of antibiotics, industrial enzymes, amino-acids, and bulk chemicals. 

Various pulping technologies for wood and other biomass have been used for centuries to produce fiber, primarily for paper production. These processes effecbvely separate and clean the cellulose for use as fiber. However, the hemicellulose and lignin byproducts are not typically used for chemical products. The depolymerized hemicellulose in pulping liquor is a large source of biomass carbohydrate that could potentially be used for chemical producbon. 

A number of reviews of the synthesis of LA from various carbohydrate sources have been published [169-173]. Approaches vary considerably in terms of selectivity and overall yield, and the reader is directed to these accounts if a detailed treatment is sought. However, given that the only competitive process for the production of LA would use biomass as feedstock, we provide in Table 2 a survey of the highest yielding approaches of this description. 

Biotechnology continues to be an important contributor to the biorefinery, especially for the conversion of carbohydrates. The paper by Richard describes a new approach for the fermentation of C sugars, providing methodology for more efficient conversion of biomass carbohydrates to EtOH. The contribution from Nakas discusses the bioproduction of polyhydroxyalkanoates using levulinic acid as a carbon source. Stipanovic describes new approaches for using hemicellulose as a chemical feedstock. 

Both in the USA and the EU, the introduction of renewable fuels standards is likely to increase considerably the consumption of bioethanol. Lignocelluloses from agricultural and forest industry residues and/or the carbohydrate fraction of municipal solid waste (MSW) will be the future source of biomass, but starch-rich sources such as corn grain (the major raw material for ethanol in USA) and sugar cane (in Brazil) are currently used. Although land devoted to fuel could reduce land available for food production, this is at present not a serious problem, but could become progressively more important with increasing use of bioethanol. For this reason, it is important to utilize other crops that could be cultivated in unused land (an important social factor to preserve rural populations) and, especially, start to use cellulose-based feedstocks and waste materials as raw material. 

When considering biomass as a source of chemical feedstock, it is also important to remember that it is not a homogeneous organic structure. The carbohydrate structures of terrestrial plants are composed of both five-carbon and six-carbon sugar polymers. The lignin component, which binds the polymers together, is an aromatic polymer of nominally propyl-methoxyphenols. In addition, there are proteins and fatty acids/oils, as well as the trace biocomponents that incorporate much of the mineral content. Therefore, processing biomass to chemical products must take into consideration both its bulk chemical structure and its components. 

The polysaccharides cellulose and hemicellulose are two major components of lignocellulosic biomass and form an abundant, non-edible and renewable source of carbohydrates. Other sources include starch, chitin, inulin and smaller... 

Irrespective of the type of biomass used for ethanol production, the biomass needs to be pretreated to make the carbohydrates available for fermentation. However, which enzymes can be used depends on the source of the biomass. In addition, the biomass needs pretreatment before the enzymes are used. The first step of the pretreatment can be of a physical nature. Once the biomass is physically pretreated, the cellulose structures are open for enzyme action. In biomass from forests, the substance is mainly in the form of cellulose. Targeted enzymes are selective for the reaction of cellulose to glucose, and therefore there are no degradation byproducts, as occurs in acid conversion technology. There are at least three ways this can be performed. Firstly, in separate hydrolysis and fermentation, the pretreated biomass is treated with cellulase, which hydrolyzes the cellulose to glucose at 50 °C and pH 4.8. Secondly, in simultaneous fermentation and saccharification (SSF) the hydrolysis and fermentation take place in the same bioreactor. Thirdly,... 

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