The influence of oxidized oils on fungal growth and lipid utilization

[摘要] English: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.

[发布机构] University of the Free State