Edible oils such as sunflower oil, soybean oil and palm oil are used today in the frying of
food. During the frying process, various changes such as removal of antioxidants, hydrolysis,
oxidation and polymerization occur in these oils. These reactions are responsible for a variety
of physical and chemical changes observed in the oil during frying and may lead to the
formation of breakdown products which include polar compounds (PCs) and polymerized
triglycerides (PTGs). South African regulations state that oils that contain 16% and more
PTGs and 25% and more PCs are harmful to human health. These oils may cause cancer and
diarrhoea in humans and animals. However, little is known regarding the effect of oxidized
oils on fungi. The oleaginous fungi Cryptococcus curvatus and Mucor circinelloides were
used to determine the effect of palm oil breakdown products, measured as PTGs on lipid
turnover, growth and morphology. In Mucor circinelloides we found, after seven days of
growth, a decrease in biomass, lipid utilization and accumulation at increased PTG levels, at
low and neutral pH. An increase in PTG concentration also influenced the morphology of M.
circinelloides. Protrusions were observed on cell surfaces when grown on oil with 45% PTGs
and not when the fungus was grown on fresh oil with 0.4% PTGs. In C. curvatus there was
also a decrease in oil utilization and biomass production at increased PTG levels, at low and
neutral pH. An increase in oil accumulation was observed at low pH while it remained
constant at neutral pH for all PTG levels tested. Hairy and warty protuberances on cell
surfaces were observed when C. curvatus was grown on oils with 15% and 45% PTGs,
respectively. It is concluded that the changes observed in lipid turnover and morphology in
both fungi are due to the presence of palm oil breakdown products. Oxidized oil breakdown
products such as aldehydes are major sources of reactive oxygen species (ROS). Studies have
shown that ROS has anti-mitochondrial action. It was also reported that acetylsalicylic acid
(ASA), an anti-inflammatory and anti-mitochondrial drug, targets structure development and
functions of yeasts, needing elevated levels of mitochondrial activity. Using antibody probes it was previously reported that sporangia of Mucor circinelloides also contain increased
mitochondrial activity yielding high levels of 3-hydroxy (OH) oxylipins. This was however
not found in Mortierella alpina (subgenus Mortierella). In this study, it is reported that
oxidized palm oil breakdown products and ASA also targets sporangium development of M.
circinelloides selectively while hyphae, with lower levels of mitochondrial activity, are more
resistant. Similar results were obtained when the anti-inflammatory compounds benzoic acid,
ibuprofen, indomethacin and salicylic acid were tested. Here, oxidized oils and antiinflammatory,
anti-mitochondrial drugs exerted similar effects on this dimorphic fungus as
found under oxygen limited conditions. Interestingly, sporangium development of M. alpina
was found not to be selectively targeted by these compounds. Mortierella alpina, which
could not expose dimorphic growth under oxygen limitation conditions, was also more
sensitive to the anti-inflammatory drugs when compared to M. circinelloides. These results
prompt further research to assess the applicability of these anti-mitochondrial antifungals to
protect plants and animals against Mucor infections. It is concluded that indications exist that
oxidized palm oil breakdown products target mitochondrial function. This may explain the
inhibitory effect of these compounds on fungal growth, lipid turnover and altered cell wall
morphology.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-10172011-133414 |
| Date | 17 October 2011 |
| Creators | Leeuw, Ntsoaki Joyce |
| Contributors | Dr M Joseph, Dr CH Pohl, Prof A Hugo, Prof JLF Kock |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-10172011-133414/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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