Handbook of Size Exclusion Chromatography and Related ...

Ball-milled straw lignin and enzymatically isolated lignin have been
extracted from wheat straw and from straw residues, respectively (77). The alkali
lignin was obtained by treatment of wheat straw with 0.5 MNaOH at 758C. The
effect of ball-milling time (BMT) on lignin yield and MM was examined. A
comparative study of ball-milled lignin, enzyme lignin, and alkali lignin using
structural determinations and SEC with an alkaline eluent was performed. The
alkali lignin, which was relatively free of polysaccharides and appeared to have
high MM, had the greatest potential for further investigation.
The effect of different hemicellulases on birch kraft pulp was evaluated by
following the amount of lignin leached from kraft pulp after enzymatic treatment
(78). An increase in the amount and MM, determined by SEC using an alkaline
eluent, of the lignin extractedfrom thexylanase-treated pulpswas observedwhen
compared to the lignin extracted from the untreated pulp.
The effect of a commmercial xylanase preparation from Trichoderma
longibrachiatum and Trichoderma harzianum E58 was tested on kraft pulp (79).
BymonitoringtheMMDofuntreatedandtreatedpulpsitwasseenthattheMMof
lignin extracted from enzyme-treated brownstock was much larger than that from
the control pulp.
Theuseofligninsfractionatedaccordingtomolarmassintheinvestigations
of effects of oxidative enzymes has been presented (80). In this system, alkaline
eluents and preparative and analytical Superdex columns were used (Fig. 4).
Neutral-detergent fibers of cotton stalks was ball-milled for different times
in a porcelain rotary ball mill and hydrolyzed by cellulase. The lignin was
extracted by either dioxane:H2O or1M NaOH (81). The effects of ball-milling
duration and extraction procedure on yield, MMD, and carbohydrate content of
lignin were investigated. The MMD patterns of the dioxane lignins were constant,
irrespectively of the ball-milling time. It was also seen that the alkali system had
probably extracted lignin molecules of larger size since the MM was two to three
times higher than that in the dioxan lignin. The results of extractions of lignin from
neutral-detergent fiber of wheat straw was performed by HP/SEC. The wheat was
ball-milled for 7, 14, 21, and 28 days in a rotary ball mill and hydrolyzed by a
cellulase for 4 days, and the residue was used for lignin extraction by either
dioxane or 1 M NaOH (81). The effects of ball-milling time and extraction
procedure on lignin yield and high-performance SEC features were examined. By
increasing the ball-milling time, an increase in the proportion of high MM fraction
was seen. MMD determinations were also used for evaluating how an enzymatic
pretreatment modified the fiber surface. The MMD was studied using 0.5 M NaOH
as eluent, a TSK HW-55S gel, and a UV detector. The MMD was determined for
lignins extracted by alkali from the enzymatically treated pulps (83). The treatment
of kraft pulp with hemicellulases removes some of the xylan and renders the fiber
structure more permeable. The increased permeability allows the passage of lignin
© 2004 by Marcel Dekker, Inc.