Qing Hua Zhou

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Sophorose lipids are a class of biosurfactants which have several industrial applications, such as in lubricants, humectants, personal care products, soaps and detergents. Environmental considerations are the driving force behind the use of biosurfactants because of their perceived advantages such as lower toxicity, biodegradability and ecological acceptability over chemical surfactants. The key factors that will determine the usage of a given biosurfactant include the development of an economic process for its production, the use of low-cost raw materials and high product yields. The objective of this study was to develop a fermentation process to produce high value biosurfactants from low- or negative cost sugars, fat and oil substrates with the yeast Torulopsis bombicola. A wide variety of sugar, nitrogen, fat and oil substrates were examined as potential feedstocks to obtain very effective carbon sources for sophorose lipids production. Experiments were carried out in shake flasks, 1-L Bellco stirred reactors and 20-L fermenter at 450 rpm and 30{dollar}\sp\circ{dollar}C using batch and fed-batch experiments. The results showed that sugar, nitrogen, fat and oil were interactive control parameters which influenced the structure, yield, growth-phase, and also the metabolic pathways leading to glycolipid production. It was found that the production of sophorose lipids increased with increasing concentrations of both oil and sugar, and was profoundly influenced by the sources and concentration of nitrogen. Corn steep liquor, yeast extract and peptone were shown to be very effective nitrogen sources for sophorose lipids production. It was found that optimal production of sophorose lipids occurred when nitrogen sources became limited. The maximal production of sophorose lipids could reach 150-160 g/L in the optimal medium consisting of 10% glucose, 10.5% canola oil, 0.1% urea, and 0.4% yeast extract in a 1-L Bellco fermenter stirred at 450 rpm, an air flow rate of 2 vvm and 30{dollar}\sp\circ{dollar}C. Similar yields of sophorose lipids were also obtained in a 20-L bioreactor. About 73% of the apolar sophorose lipid, which has been described as 17-L-((2{dollar}\sp\prime{dollar}-O-{dollar}\beta{dollar}-D-glucopyranosyl-{dollar}\beta{dollar}-D-glucopyranosyl) -oxy)-octadecanoic acid 1{dollar}\sp\prime{dollar}-4{dollar}\sp{lcub}\prime\prime{rcub}{dollar}-lactone 6{dollar}\sp\prime{dollar},6{dollar}\sp{lcub}\prime\prime{rcub}{dollar}-diacetate (SL-1) group, was found in the mixture of sophorose lipids produced under the above conditions. When only lactose was present as the sugar source in the medium, the yeast Torulopsis bombicola did not grow. However, in the presence of both lactose and olive oil intra- and extracellular lipids were synthesized. By fed-batch cultivation, it could be seen that the maximization of yields, productivity and the minimization of production costs of sophorose lipids were obtained because the production phase was extended and substrates and enzymes were utilized very effectively. Sets of kinetics models for batch and fed-batch fermentation processes for the growth and sophorose lipids by Torulopsis bombicola were proposed, which could successfully describe, control and predict the kinetics of cell growth and sophorose lipids production.



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