Scytalidium thermophilum is a termophilic fungus that effectively produces the
extracellular enzyme catalase phenol oxidase (CATPO). The enzyme is distinct
among catalases with its bifunctionality of oxidising phenolic compounds in the
absence of H2O2. CATPO is capable of oxidizing catechol, chlorogenic acid,
caffeic acid and catechin which are ortho &ndash / diphenolic compounds. Diphenolic
compounds are known as strong antioxidants. Catalase is one of the important
antioxidant enzymes. Therefore, in this thesis the effect of CATPO on the final
antioxidant capacity of the oxidized products was analysed. Antioxidant capacity
measurements of oxidized and unreacted phenolic compounds were done using
the two widely used methods TEAC and FRAP.
CATPO oxidized catechol showed 2.4 fold increase when compared to its nonoxidized
form, which was highest among others. Catechol was followed by
caffeic acid, chlorogenic acid, and catechin. This finding is new to the literature
and may be of importance to the antioxidant mechanism of organisms. Results
have also shown that the most well known phenol oxidases, laccase and
tyrosinase, do not result in such high increases in antioxidant capacity upon
oxidation of the substrates tested. Due to this finding, as a possible means of
applying CATPO to increase the antioxidant capacity of products daily consumed,
tea was selected.
Tea is the second most consumed beverage after water and it is known to
possess high amounts of flavanols. Green tea is rich in catechins whereas black
tea is a rich source of theaflavins and thearubigins. Fermentation is a critical
process for production of good quality tea and is the key step differing between
green and black tea production. During this process phenol oxidases catalyze the
oxidation of polyphenolic compounds present in tea leaves to their
corresponding o-quinones. Utilization of CATPO in tea samples resulted in an
increase in antioxidant capacity and its effect was enhanced by an increase in
brewing time. Interestingly, the addition of sugar decreased antioxidant capacity.
Laccase and tyrosinase were ineffective in increasing the antioxidant capacity of tea samples.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12615049/index.pdf |
| Date | 01 September 2012 |
| Creators | Soyler, Ulviye Betul |
| Contributors | Ogel, Zumrut Begum |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | text/pdf |
| Rights | Access forbidden for 1 year |
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