Sugar platform, biomass fermentation

Platform compounds are further converted to products by microbial fermentation processes. Saccharification and fermentation can be accomplished in a sequential process by separate hydrolysis and fermentation (SHF), or in a consolidated one-pot process known as simultaneous saccharification and fermentation (SSF) of single sugars or simultaneous saccharification and co-fermentation (SSCF) of all monosaccharides. Future developments might even combine the production of saccharolytic enzymes, the hydrolysis of cellulose, and hemicellulose to monomeric sugars and the fermentation of hexose and pentose sugars in a single process, the so-called consolidated biomass processing (CBP) (Menon and Rao 2012). 

Early efforts for the efficient conversion of biomass into monomers were concentrated on the acidic transformation and on the fermentation of sugars obtained from sucrose, or from glucose after depolymerization of starch materials (potato, com). During the last two decades, however, more attention has been focused on other constituents of plant materials, such as cellulose and lignocellulosic residues. The current trend is indeed to avoid competition with food, offering new routes to C6 and C5 carbohydrates, for further transformation into value-added platform molecules. 

Pine hydrolyzate consists of higher concentrations of mannose and lower concentrations of xylose. Since mannose is a fermentable sugar compared to xylose, the elevated presence of mannose in the pine tree makes it more viable for fermentation and subsequent platform chemical production. Taherzadeh et al. (1997) reported that the pine tree biomass is easily hydrolyzed to fermentable sugars when compared to other softwoods. Moreover, these authors have reported that the maximum fermentable sugars were obtained from comparing with those of all the wood species examined in that study (Table 16.2). 

Sweet sorghum has become a new alternative raw material for bioethanol production in the US, due to its low water requirements, adaptability to different sods, nitrogen- and radiation-use efficiency, genetic diversity, and potential for the production of food, feed, and biofuels. It contains both fermentable free sugars and lignocellulosic biomass, susceptible to produce biofuel (Platform, 2015). 

---