Utilisation of edible oils and GLA production by Mucor in the presence of acetate

[摘要] English: Surveys launched across South Africa indicate that many fryingestablishments abuse their frying oils and fats during the frying process,resulting in degradation and concomitant production of potentially toxicoxidation products. Some of these compounds have been shown to be toxicto animals and in human in vitro studies. Consequently, strict regulationsunder the Foodstuffs, Cosmetics and Disinfectants Act, 1972 (Act 54 of 1972)were published on 16 August 1996. It is now an offense to use or sell usedcooking oil or fat for human consumption containing high levels of thesedegradation products. Since frying establishments are not allowed to discardtheir used oils and fats by selling to the public for consumption or dumpinginto municipal drainage systems, it is important that these oils and fats arecollected for re-use in another form. Consequently, the aim of this study wasthe biotransformation of used oil wastes (containing no toxic substances) tohigh value lipids containing gamma-linolenic acid (GLA). This polyunsaturated fatty acid is prescribed for the treatment of eczema. In orderto achieve this, Mucor circinelloides f. circinelloides CBS 108.16 was firstgrown on 40 gil unused sunflower oil and, as expected, produced neutrallipids (NL) similar in fatty acyl composition to the original oil. The apparentrepression of the Á6 fatty acid desaturation was partially reversed when cellswere grown on oil (30 g/l) and sodium acetate (10 gil) as mixed substratesresulting in an increase in GLA content. Furthermore, a three-fold increase inoil substrate utilisation and doubling of biomass production to 19.1 giloccurred when sodium acetate was added to the oil substrate. When sodiumacetate (10 gil) was added to a growth medium containing used cooking oil(UCO) similar results were obtained. This experimental procedure was repeated for seven additional Mucor strains and again the stimulatory effectof sodium acetate in combination with UCO was obvious. Next, the effect ofdifferent UCO concentrations in the presence of 10 g sodium acetatell onbiomass and lipid production was investigated in Mucor circinelloides CBS108.16. According to our results, a maximum biomass concentration of 48 gIlconsisting of 82 % oil yielding about 35 g NUl and up to 900 mg GLNI wasachieved. The addition of 30 g UCO/I in combination with 10 g sodiumacetate/l proved to be the optimum UCO concentration in order to obtainmaximum GLA yield. Similar results with this strain were obtained when UCOwas replaced with fresh unused cooking oil. When these experiments wererepeated with linseed oil and sodium acetate as sole carbon sources, muchless GLA was produced (351 mg GLNI). According to bioreactor studies, theeffects of sodium acetate addition can be attributed to the change in pH of themedium during cell growth in the presence and absence of acetate. In the absence of sodium acetate the pH decreased to 2.2, whereas in its presenceit increased to about pH 8.0. During metabolism of sunflower oil in thepresence of sodium acetate, the percentage of saturated fatty acids in theextracellular lipids increased, suggesting a higher specificity of the fungallipase for unsaturated fatty acids. When the sodium acetate was omitted fromthe medium and the pH gradually increased according to a pH profilemimicking the natural increase in pH found in the medium containing sodiumacetate, similar results as in the presence of sodium acetate were obtained.This observation indicated that the pH increase alone during cultivation wasresponsible for the increased sunflower oil utilisation, biomass and GLAproduction.

[发布机构] University of the Free State