The production of citric acid by Yarrowia lipolytica when cultivated on edible and waste fats
| dc.contributor.advisor | Kock, J. L. F. | |
| dc.contributor.advisor | Smit, M. S. | |
| dc.contributor.advisor | Hugo, A. | |
| dc.contributor.author | Venter, Tania | |
| dc.date.accessioned | 2017-11-01T09:07:16Z | |
| dc.date.available | 2017-11-01T09:07:16Z | |
| dc.date.issued | 2003-11 | |
| dc.description.abstract | English: Large amounts of edible fat waste (approx. 100 000 tons p.a.) are generated in South Africa when edible fats, mainly sunflower fat, are used in frying processes. When these fats are overexposed to heat a part of this fat waste becomes toxic to humans. Another part of these fat waste (approx. 50%) are however still fit for human consumption and has been discarded by frying establishments while within regulatory limits. Consequently these wastes have the potential to be processed to safe usable foodstuffs such as citric acid which is mainly imported to South Africa. Since it was shown that Yarrowia lipolytica can convert monounsaturated fats (such as canola fat) to citric acid, the aim of this dissertation became to explore the possibility of this yeast to convert the low cost waste product i.e. used edible fat waste (still fit for human consumption) to a more valuable product such as citric acid in the presence of acetate. In order to achieve this, eighteen strains of Yarrowia lipolytica were grown for 6 days on a medium consisting of 30 g/l sunflower fat in the presence and absence of 10 g/l acetate. It was discovered that the addition of acetate caused a drastic increase in citric acid production by many strains of Yarrowia lipolytica. Strikingly Yarrowia lipolytica UOFS Y-1701 produced increased amounts of citric acid in the presence of acetate i.e. 0.5 g/l in the absence of acetate to 18.7 g/l in the presence of acetate. Similarly, the ratio of citric acid : isocitric acid increased significantly from 1.7:1 in the absence of acetate to 3.7:1 in the presence of acetate after 240 h of growth. During the growth period the acetate as well as the 30 g/l fat was almost completely utilized (100% and 99.3% respectively). This same experiment was repeated, but this time with 30 g/l simulated sunflower fat waste (PTGs = 11%) together with 10 g/l acetate, and as control, 40 g/l simulated sunflower fat waste without acetate. Very low citric acid concentrations were obtained when Yarrowia lipolytica was cultivated in simulated sunflower fat waste in the presence (maximum of 1.0 g/l) and the absence (maximum of 0.3 g/l) of acetate. When the effects of increased levels of acetate and PTGs were calculated on the basis of a 22 factorial design and by interpreting responses in both Chapters 2 and 3, the following were found: (1) The addition of 10 g/l acetate showed a large increase of +4.7 units in citric acid production. This effect was cancelled (citric acid production dropped by –4.7 units) when the PTG levels increased by 10% (m/m). (2) The addition of 10 g/l acetate lead to an increase (+4.1 units) in biomass production while the increase in PTGs decreased its production by –2.3 units. (3) When 10 g/l acetate was added, a large increase in extracellular lipids (i.e. sunflower fat and waste) utilization occurred (+12.0 units) while the opposite was true (extracellular lipids decreased by –7.6 units) when the PTG level increased by 10% (m/m). (4) Interestingly, the intracellular lipids increased in cells when both acetate and PTG levels were increased (i.e. increased by +6.0 and +2.9 units respectively). (5) Furthermore, the pH increased when both acetate (by +0.7 units) and PTG levels (by +0.3 units) were raised. These results indicate that low cost used frying fat waste is probably not a good substrate for citric acid production. | en_ZA |
| dc.description.abstract | Afrikaans: In Suid-Afrika word daar jaarliks ‘n groot hoeveelheid eetbare afval vet gegenereer vanaf verskeie braai-prosesse (omtrent 100 000 ton p.j.). Wanneer hierdie vet (meestal sonneblom vet) uitermatig blootgestel word aan hitte, word ‘n gedeelte hiervan giftig vir menslike gebruik. Die oorblywende gedeelte (omtrent 50%) van hierdie afval vet is steeds aanvaarbaar vir menslike gebruik en word soms onnodig deur braai-instellings weggegooi, al voldoen dit steeds aan wetlike vereistes. Díe afval vet het die potensiaal om na veilige, bruikbare voedsel-produkte omgeskakel te word, bv. sitroensuur (wat meestal ingevoer word na Suid-Afrika). Dis reeds bewys dat Yarrowia lipolytica mono-onversadigde vette (soos kanola vet) na sitroensuur kan omskakel. Juis om hierdie rede het die doel van hierdie dissertasie die volgende geword: om die moontlikheid van Yarrowia lipolytica te bestudeer om vanuit ‘n lae-koste afval produk soos eetbare afval vet (steeds aanvaarbaar vir menslike gebruik), ‘n waardevolle produk soos sitroensuur, te vervaardig. Om dit te bereik, het ons begin deur agtien stamme van Yarrowia lipolytica vir ses dae te groei op ‘n medium bestaande uit 30 g/l sonneblom olie in die teenwoordigheid en afwesigheid van 10 g/l asetaat. Gevolglik het die toediening van asetaat, ‘n drastiese toename in sitroensuur produksie getoon by die meeste van die Yarrowia lipolytica stamme. Veral Yarrowia lipolytica UOFS Y-1701 het uitsonderlik hoë konsentrasies sitroensuur opgelwer in die teenwoordigheid van asetaat. Soortgelyke toenames in die verhouding van sitroensuur : isositroensuur is opgemerk na 24 h van groei: van 1.7:1 in die afwesigheid van asetaat, tot 3.7:1 in die teenwoordigheid van asetaat. Die asetaat, asook die 30 g/l vet is byna heeltemal benut tydens die 240 h groei periode (100% en 99.3% respektiewelik). Dieselfde eksperiment is herhaal, maar díe keer met 30 g/l gesimuleerde sonneblom afval vet (gepolimeriseerde trigliseriede (PTGs) = 11%) saam met 10 g/l asetaat en, as ‘n kontrole, slegs 40 g/l gesimuleerde sonneblom afval vet sonder asetaat se toediening. Baie lae sitroensuur konsentrasies was verkry toe Yarrowia lipolytica op gesimuleerde sonneblom afval vet gegroei is: ‘n maksimum van 1.0 g/l in die teenwoordigheid van asetaat en 0.3 g/l in die afwesigheid van asetaat. Toe die effekte van die verhoogde asetaat en PTG vlakke bereken is volgens ‘n 22 faktoriale ontwerp en die response van beide hoofstukke 2 en 3 geïnterpeteer was, is die volgende gevind: (1) Die toediening van 10 g/l asetaat het gelei tot ‘n geweldige toename van +4.7 eenhede in sitroensuurproduksie. Hiedie effek is wel gekanselleer (sitroensuur produksie daal met –4.7 eenhede) toe PTG vlakke met 10% (m/m) verhoog is. (2) Die toevoeging van 10 g/l asetaat het gelei tot ‘n toename (+4.1 eenhede) in biomassa produksie, terwyl die toename in PTGs gelei het tot ‘n afname in díe produksie (-2.3 eenhede). (3) Wanneer 10 g/l asetaat bygevoeg word, is daar ‘n groot toename in die verbruik van die ekstrasellulêre lipiede (sonneblom vet en afval) van +12 eenhede, terwyl die teenoorgestelde opgelet is (ekstrasellulêre lipiede neem af met –7.6 eenhede) toe die PTG vlak verhoog is met 10% (m/m). (4) Dit is interessant om te sien dat die intrasellulêre lipiede toegeneem het in die selle wanneer beide asetaat en PTG vlakke verhoog is (bv. verhoog met +6.0 en +2.9 eenhede respektiewelik). (5) Verder het die pH ook verhoog toe beide asetaat (met +0.7 eenhede) en PTG vlakke (met +0.3 eenhede) toegeneem het. Hierdie resultate is ‘n aanduiding dat lae koste gebruikte braai-vet afval nie ‘n goeie substraat is vir die produksie van sitroensuur nie. | af |
| dc.identifier.uri | http://hdl.handle.net/11660/7376 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Citric acid -- Biotechnology | en_ZA |
| dc.subject | Oil industries -- Waste disposal | en_ZA |
| dc.subject | Oils and fats, Edible | en_ZA |
| dc.subject | Yarrowia lipolytica | en_ZA |
| dc.subject | Sunflower | en_ZA |
| dc.subject | Lipids | en_ZA |
| dc.subject | Edible oil waste | en_ZA |
| dc.subject | Polymerized triglycerides | en_ZA |
| dc.subject | Glyoxylate cycle | en_ZA |
| dc.subject | Acetate | en_ZA |
| dc.subject | Dissertation (M.Sc. (Microbial, Biochemical and Food Biotechnology))--University of the Free State, 2003 | en_ZA |
| dc.title | The production of citric acid by Yarrowia lipolytica when cultivated on edible and waste fats | en_ZA |
| dc.type | Dissertation | en_ZA |