Environmental Engineering Reference
In-Depth Information
Some tannin-rich sources and several microorganisms [1, 51, 94, 95] have been
used for gallic acid production and the hydrolytic enzyme responsible for its produc-
tion is the tannase or tannins acyl hydrolase (EC, 3.1.1.20). It has also been reported
earlier that tannase also can hydrolyse ellagitannins. However, the results of this
study did not show this pattern and hence we consider that this enzyme is unable to
degrade ellagitannins.
Results are in agreement by Shi et al. [75] on SSF of valonea tannins (79.2% at
168 h). This lower rate of hydrolysis could be due to low protein levels in the pheno-
lics extracts of valonea. However, Belmares-Cerda et al. [96] reported better results
with both substrates tested in this study using
A. niger
. This could be explained
by fact that the earlier studies used leaves, a direct source of creosote and tar
bush. This source contained high content of protein and tannins-protein complexes
[97]. Several fungal species as
Penicillium, Chaetomium
,
Fusarium
,
Rhizoctonia
,
Cylindrocarpon
, and
Trichoderma
[98] were reported to use the monomers of gallic
acid as substrate by the oxidative breakdown to simple oxidative acid, which then
enter to citric acid cycle [99] and is converted to pyrogallol.
Important advances in EA production from ellagitannins have been reported in
submerged co-cultures by Huang et al. [77-79] Recently, high EA yields (24%)
were obtained after optimization of the co-culture of
A. oryzae
with
Trichoderma
reesei
using acorn cups extract containing up to 62% ellagitannins as substrate [79].
However, in SSC the information is limited to those studies reported by Vattem and
Shetty [100, 101], using cranberry pomace as support and source of ellagitannins
with very low EA yields. Huang et al. [79]. suggested for the first time, the presence
of ellagitannin acyl hydrolase as the enzyme responsible of the EA accumulation,
which indicates that a new tannase is involved in the biodegradation ellagitannins.
Also, they reported that such enzyme had a synergistic activity with other enzymes
as xylanase and cellulase to enhance the EA accumulation. However, further studies
are needed to define the catalytic role and properties of this new EHA or ellagi-
tannin acyl hydrolase detected. Aguilera-Carbo et al. [82] reported that the SSF of
A. niger
GH1 using creosote bush ellagitannins impregnated in polyurethane foam
could remarkably enhance EA accumulation.
The possibility to release NDGA from fermentation of
Larrea tridentata
was evi-
denced for the first time by Mercado Martinez [102], and high yields were reported.
More than 75% of NDGA contained in the plant was recovered after fermentation
process (Fig. 7 ). However, more efforts are needed to enhance NDGA accumula-
tion and to improve the biotechnological process. Creosote bush is the best source
of NDGA and gallic acid while pomegranate husk is the best source of ellagic acid.
5 Current Commentary and 5 Year View
The production of antioxidant phenolics by SSF is considered as an emerging tech-
nology in last five years. New information is being reported each year regarding
new substrates, molecules, and procedures for recovery of the antioxidants. Also,
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