Microbial Production of Potent Phenolic-Antioxidants Through Solid State Fermentation - Sustainable Biotechnology: Sources of Renewable Energy - page 238

and ellagic acid). These fungal strains have demonstrated their capacity to degrade
hydrolysable tannins and norlignans and to make possible the resultant accumula-
tion of monomers which can be either consumed or accumulated during the process.
The creosote and tar bush was determined to be the best sources of antioxidants.
The highest consumption of total phenols in the samples collected at 48 h of SSF
process was recorded. The initial concentration of total phenols in unfermented cre-
osote bush extracts was 7.29 mg/g of plant; that was diminished up to 6.04 mg/g of
plant after 48 h of fermentation. The total phenol in raw tar bush was 2.009 mg/g
of plant that was diminished up to 1.001 mg/g of plant after 48 h of fermenta-
tion. Results revealed that Aspergillus niger PSH degrades the hydrolysable tannin
polymers present in phenolic extract of both plants.
The monomers obtained by the hydrolysis of this kind of tannins were consumed
by the fungus within 48 h of fermentation, and then the hydrolysis products were
accumulated. However, it was observed that the monomers of condensed tannins
were not consumed. The hydrolysable tannins present in the creosote bush extracts
were utilized by 16% during the first 72 h of fermentation. At 96 h, the hydrolysable
tannins were degraded and approximately 15% of monomers of phenolic acids
were accumulated. In tar bush extracts the hydrolysable tannin consumption was
approximately 40% at 48 h of fermentation.
The microbial biodegradation of condensed tannins and the respective catechin
monomers accumulation were proportional to the culture time. The fungus strain
recorded a similar behaviour in the fermentation kinetics of both substrates tested.
The highest concentration of condensed tannins was reached at 96 h of fermenta-
tion process. An increase of condensed tannins from 42 and 83% were observed
using creosote and tar bush extracts, respectively. The accumulation of gallic acid
indicated the depolymerization of gallotannins and that this substance can be used
as substrate. A. niger PSH consumed nearly 72% of free gallic acid in the extract,
the minimum concentration reported was 0.14 mg/g of creosote bush at 48 h of the
process. After this time, an accumulation of gallic acid was observed and this could
be due to the reason that the rate of gallotannins hydrolysis was faster than the con-
sumption rate of gallic acid. At 96 h, there was an increment in gallic acid by 152%
with the concentration of 0.48 mg/g of creosote bush. In the fermentation of tar
bush extracts, the gallotannis were depolymerised after 48 h followed by releasing
of glucose and gallic acid. The highest level of gallic acid was reported at 96 h and
was 0.08 mg/g of tar bush. Biodegradation of ellagitannins to ellagic acid and its
accumulation was proportional to the fermentation time for both substrates. Initial
ellagic acid concentration was 2.72 and 2.49 mg/g of tar and creosote bush respec-
tively. After 96 h, the ellagic acid accumulated nearly by 92 and 177% in creosote
and tar bush extracts respectively (Fig. 6). The highest consumption of total phenols,
hydrolysable tannins in the phenolic extracts of both plants was recorded at 48 h of
fermentation reaction. This could be due to the fact that the phenolic extracts of
both plant materials have complex polysaccharides, and moreover the strain studied
preferred to consume free monophenols and glycosides like gallic acid and glucose
respectively present in the extracts before the production of hydrolytic enzymes to
degrade tannins.