Hydrolysates, hardwood/softwood

Candida utilis is grown on sulfite waste Hquor in Western Europe and North America, on sugar cane molasses in Cuba and Taiwan and on ceUulose acid hydrolysates in Eastern Europe and the former Soviet Union. C. ///i/if utilizes hexoses, pentoses, and many organic acids. Sulfite Hquor from hardwoods contains 2—3% fermentable sugars of which 20% are hexoses and 80% pentoses in softwood Hquors the proportions are reversed. The SO2 must be stripped out to allow yeast growth, which is carried out in large, highly-aerated fermentors. Eor continuous fermentations, carried out at pH 4 and 30°C, the dilution rate is 0.27—0.30 (34). 

It is well known that phenolic compounds are important inhibitors in hydrolysates prepared from hardwood (27) as well as softwood (20). The hydrophobicity of the matrix is likely to be an important property that contributes to the ability of an ion-exchange resin to remove phenols. Although the knowledge regarding the suitability of different methods to determine phenolics in lignocellulose hydrolysates has increased (28), the quantification of phenolics and the correlation with the inhibitory effect is still a challenging task, because hydrolysates contain a wide variety of phenolic compounds that have very different toxic effects. 

Inhibitory furaldehydes in lignocellulose hydrolysates include 2-furaldehyde (furfural) and 5-hydroxymethyl-2-furaldehyde (HMF) (Fig. 2). The concentrations of furfural and HMF in lignocellulose hydrolysates are highly dependent on the raw material and on the conditions used for acid hydrolysis. Softwood acid hydrolysates contain low amounts of furfural compared with HMF [58]. Hardwood hydrolysates, which contain high concentrations of pentoses, the precursors to furfural, contain more similar amounts. Several recent investigations [102-105] deal with the effect of the furaldehydes on S. cerevisiae and the conversion of furfural to furfuryl alcohol and HMF to 5-hydroxymethyl-fur-furyl alcohol by S. cerevisiae. The presence of the furaldehydes causes lag phases in the formation of biomass and ethanol. 

Table 3A.7 Chemical composition of hardwood- and softwood-derived hydrolysates (%ofinitial wood dry matter) ...

In a classical hydrolyses is obtained cellulose rod-like nanocrystals or nanocrystal systems from hardwood and softwood (Beck-Candanedo et al. 2005) or whiskers (Bondenson et al. 2007) or rod-Uke nanoparticles (Mesquinfam et al. 2011)... 

Under alkaline cooking conditions some of the 4-0-MeGlcA residues present in hardwood and softwood xylans are converted into unsaturated hexenuronic acid residues (HexA) by -elimination of methanol. In an early study (4) employing MALDI-MS, we were able to identify a number of different HexA and 4-0-MeGlcA containing xylooligosaccharides in the hydrolysate obtained after endoxylanase treatment of an unbleached hardwood kraft pulp. 

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