No abstract

Steam explosion after sulphur dioxide impregnation of wood chips is an effective method for improving the enzymatic digestibility of cellulose in the softwood Pinus radiata. Digestibility of pretreated fiber was progressively increased by altering the conditions of steam explosion. With increasing digestibility, there was an observed increase in fiber porosity as measured by the solute exclusion technique. Accessible pore volume and accessible surface area to a 5-nm dextran probe positively correlated with both 2- and 24-h digestion yields from pretreated fiber. The increase in accessibility was probably the result of hemicellulose extraction and lignin redistribution. A subsequent loss in accessibility, brought about by structural collapse or further lignin redistribution, resulted in a corresponding loss in digestibility. It appears that steam explosion increases cellulose digestibility in P. radiata by increasing fiber porosity.

An experimental optiialsation procedure has been used to investigate steam explosion of Pinus radiata. Enzymatic digestibility of this softwood is enhanced by s t e m oxplosion and addition of sulphur dioxide greatly Improves effectiveness of the process. The effects of the variables time, temperature, and sulphur dioxide level have been described by empirical models. The response parameters modelled are: dry-matter yield: water-iruolublo fibro yield: uater-soluble sugar yield; enzymatic-hydrolysis sugar yield: and total sugar yield. Near optimal total sugar yields were obtalned with the conditions: 3 rlnutes; 215.C; and 2.55% sulphur dioxide. Under these conditions the stoiu-exploded fibre was 8 a digestible (cellulose to glucose) by the cellulase enzymes used. and a total sugar yield oE 57 g/100 g 0 . d . uood uas obtalned. T h i s study has shown that soEtuoods, of which Pinus radiata is typical, CM be lade as aenable to hydrolysis by cellulase enzymes as hardwoods. mi& have previously been considered the only viable substrates for such processes. DpEBowcpION Steam explosion is recognised as one of the most cost effective pretreatments for hardwoods and agricultural residues prior to enzymatic sa~charification~-~. As a pretreatmnt for 373 Copyrilht 0 1987 by M a s e l Dekkor, Inc. Downloaded by [FU Berlin] at 06:10 04 December 2014 374 CURY AND HACKIE softwoods. however, steam explosion has been considerad ineffective, although for reasons which have not been made 4 , 5 clear . The Softn#d, Pinru radiaca i s the predoRiMnt CUmerCial forest species in Mew Zealand and large quantities of forest and mill residues (sawdust, shavlngs and chips) will bccane available over the next 10 to 20 years for use in fuel or chemical production processes . Research into improving the effectiveness of steam explosion on this softwood species uas Initiated to assist utilisation of such residues. 6 The treatment of both softwoods and hardwoods with high levels of gaseous sulphur dioxide at 120.C was shom by PIillet et 61.' to significantly improve enzymic digestibility of the yoody substrates. Subsequently, research at General Blectri~"~, Fmrolvlng addition of low levels of sulphur dioxide during true stean explosion. c m f W the beneficial effects of sulphur dioxide addition. However, whereas Hillet et al. attributed these effects to delignification, the latter group showed that the improved enzymatic digestion of poplar wood resulted frcm a more complete removal of hanicelluloses. The addition of sulphuric acid or sulphur dioxide during steam explosion of the hardmod pow lus treeuloides (aspen) has also been shown to be beneEicia1 in terms of haicollulose rawwal and improved enzymatic digestibility. 9 Recent work involving prehydrolysis of woody substrates with and without the addition of acid catalysts has shown that improved carbohydrate survival and better hemicellulose removal are obtained when the treatment pH is la#, around pH 2-3. Without catalyst addition. the pH attained during autohydrolysis is around pH 3-4. and, at ...

Sugar solutions obtained by dilute acid hydrolysis of the softwood Pinus radiata contain various wood‐derived components which are inhibitory to the ethanolic fermentation by the yeast Saccharomyces cerevisiae. A detailed examination of these compounds indicated that a range of low molecular weight phenolics, related in structure to ‘Hibberts ketones’, may be identified as the most inhibitory materials. These lignin‐based compounds, although present at low levels compared with the carbohydrate‐degradation compounds, are approximately 10 times more inhibitory.

Summary Transmission and diffuse reflectance FTIR spectra of samples of Pinus radiata wood have been used as the basis of PLS-1 (partial least squares) and PLS-2 (projection to latent structures) models for the prediction of extractives, lignin, total carbohydrate and basic density. Very little difference was observed between models based on transmission spectra and those based on diffuse reflectance spectra. Because of the ease of sample preparation and presentation the diffuse reflectance technique was chosen as the method of preference. Similarly very little difference was observed between models prepared using PLS-1 and models prepared using PLS-2 correlations of diffuse reflectance spectra. Multiple correlation coefficients between the four measured properties and the diffuse reflectance spectra using PLS-2 modelling with four principal components are respectively: extractives, 0.87; Klason lignin, 0.84; total carbohydrate, 0.58; and density, 0.87.