Biokonversi gentia.n kelap a sa wit kepada protein sel tunggal dan etanol
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Date
1995
Authors
Abdul Aziz, Astimar
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Abstract
Palm Press Fibre (PPF) used for this study shows that it contains,
on dry basis, a.-cellulose 32.4%, lignin 23.3% and pentosans 15.6%.
For the hydrolysis of pentosans, enzymatic process was found to be
inaffective and hence, mild acid hydrolysis was used for the preparation of
prehydrolysate containing xylose from pentosan. Studies of factors
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affecting prehydrolysis included effects of particle size, acid
concentration, temperature, time and solid-liquid ratio. Under optimised
conditions of particle size 0.4 mm ( 400 micron), concentration of H2S04
0.7% (w/v), temp. 125 oc (15.6 psi), period of 2 hrs and solid-liquid ratio
of 1:5, the highest yield of xylose from untreated PPF was 44.5 g/L
(22.3% conversion based on dry PPF) and that from PPF treated with
glacial acetic acid (1 g PPF to 0.4 mL) and sodium chlorite (I g PPF to
1. 5 g) at 70-80 °C was 67.8 g/L (23. 9% based on dry PPF). Sample
treated with 1% (w/v) NaOH at 100 °C for 2 hrs was found to give 23.2
g/L xylose.
Cellulosic residue after mild acid hydrolysis and the removal of
hemicellulose part was hydrolysed using cellulase (720 IU/g. PPF) and
cellobiase (62.5 IU/g. PPF) at pH 4.8, temp. 48 oc and under agitation at
150 rpm. The maximum aments of reducing sugars obtained were 3 5. 5,
18.8 and 9. 8 g/L from the three residues respectively collected from three
types of treatments during tnild acid hydrolysis. The first deals with the
treatment of PPF by acetic acid and sodium chlorite followed by mild
hydrolysis, the second covers PPF treated with alkali (I%, w/v, at
1 00 °C), whereas the third one is for untreated PPF which was under
direct acid hydrolysis. The ~ample without any pretreatment gave lowest
reducing sugars of 2.3 g/L 6nly. The yield of reducing sugars was found
to improve highly reaching 70 g/L ( 44.8 % conversion based on dry PPF)
when the cellulosic residue from the third case above was treated with 1%
(w/v) NaOH at 121 °C (15 p~i). This integrated process was then selected
for the preparation of both hydrolysates from hemicellulose and cellulose
parts of PPF.
Furfural, which is a side product in acid hydrolysis, was inhibitory
to microbial growth during fermentation if in high concentration.
However, at furfural concentration of 1.1 g/L together with 45.7 g/L of
xylose. from the modified process of acid hydrolysis, 0.8% (w/v) H2S04
for 90 minutes, gave the minimum effects of inhibitory. Trifluoroacetic
Acid (TFA) was also tried and min~mum amount of furfural produced was
3.3 g/L with xylose yield of 23.2 g/L when 2 M TFA was used at 100 oc
for 330 minutes. Thus, mild hydrolysis with H2S04 was followed for the
preparation of prehydrolysate.
The prehydrolysate containing 45.7 g/L xylose was found to be a
good medium for the growth of Candida uti/is . Under optimised
fermentation conditions of ~H 5.5, temp. 32 °C, agitation of 150 rpm,
dilution ratio of I :2 and period of 72 hrs, the highest yield of edible
biomass (C. utilis) obtained was 20.6 g/L (0.66 mg/mg dry cell weight).
The suitability of this PPF prehydrolysate as the fermentation medium for
edible protein production had been compared to that of when pure
solution of xylose (23 g/L) was used as a fermentation medium and it was
found that it produced 22.4 g/lLbiomass (protein content of 0.60 mg/mg
dry cell weight).
Similarly, the cellulose hydrolysate with 70.0 g/L of reducing
sugars was found to be a suitable fermentation medium for Saccharomyces
cerevisiae for the production of ethanol. The maximum amount of ethanol
produced was 20 g/1 (57% conversion based on reducing sugars or 25.6%
based on initial PPF) when the fermentation was run under its optimum
conditions of pH 4.8, temp 30 °C, agitation rate of 200 rpm, dilution ratio
of 1:2 and the fermentation period of 24 hours. For this purpose, the
necessary anaerobic conditions were maintained inside the fermentor using
continuous supply of nitrogen.
Description
Keywords
Gentia.n kelapa sawit , Sel tunggal , Etanol