Production and effect of aldonic acids during enzymatic hydrolysis of lignocellulose at high dry matter content

Publikation: Bidrag til tidsskriftTidsskriftartikelfagfællebedømt

  • David Cannella
  • Chia-Wen Hsieh
  • Claus Felby
  • Henning Jørgensen
Abstract
Background: The recent discovery of accessory proteins that boost cellulose hydrolysis has increased the
economical and technical efficiency of processing cellulose to bioethanol. Oxidative enzymes (e.g. GH61) present in
new commercial enzyme preparations have shown to increase cellulose conversion yields. When using pure
cellulose substrates it has been determined that both oxidized and unoxidized cellodextrin products are formed. We
report the effect of oxidative activity in a commercial enzyme mix (Cellic CTec2) upon overall hydrolysis, formation
of oxidized products and impact on ß-glucosidase activity. The experiments were done at high solids loadings
using a lignocellulosic substrate simulating commercially relevant conditions.
Results: The Cellic CTec2 contained oxidative enzymes which produce gluconic acid from lignocellulose. Both
gluconic and cellobionic acid were produced during hydrolysis of pretreated wheat straw at 30% WIS. Up to 4% of
released glucose was oxidized into gluconic acid using Cellic CTec2, whereas no oxidized products were detected
when using an earlier cellulase preparation Celluclast/Novozym188. However, the cellulose conversion yield was
25% lower using Celluclast/Novozym188 compared to Cellic CTec2. Despite the advantage of the oxidative
enzymes, it was shown that aldonic acids could be problematic to the hydrolytic enzymes. Hydrolysis experiments
revealed that cellobionic acid was hydrolyzed by ß-glucosidase at a rate almost 10-fold lower than for cellobiose,
and the formed gluconic acid was an inhibitor of the ß-glucosidase.
Interestingly, the level of gluconic acid varied significantly with temperature. At 50°C (SHF conditions) 35% less
gluconic acid was produced compared to at 33°C (SSF conditions). We also found that in the presence of lignin, no
reducing agent was needed for the function of the oxidative enzymes.
Conclusions: The presence of oxidative enzymes in Cellic CTec2 led to the formation of cellobionic and gluconic acid
during hydrolysis of pretreated wheat straw and filter paper. Gluconic acid was a stronger inhibitor of ß-glucosidase than
glucose. The formation of oxidized products decreased as the hydrolysis temperature was increased from 33° to 50°C.
Despite end-product inhibition, the oxidative cleavage of the cellulose chains has a synergistic effect upon the overall
hydrolysis of cellulose as the sugar yield increased compared to using an enzyme preparation without oxidative activity.
OriginalsprogEngelsk
TidsskriftBiotechnology for Biofuels
Vol/bind5
Udgave nummer26
Antal sider10
ISSN1754-6834
DOI
StatusUdgivet - 2012

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