Physiological and Biochemical Characterization of Yeasts Active in the Degradation of Cheese Whey to Glycerol, Ethanol and 2,3-Butylene Glycol
Jenq, Wheamei
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https://hdl.handle.net/2142/70103
Description
Title
Physiological and Biochemical Characterization of Yeasts Active in the Degradation of Cheese Whey to Glycerol, Ethanol and 2,3-Butylene Glycol
Author(s)
Jenq, Wheamei
Issue Date
1988
Doctoral Committee Chair(s)
Speckman, Ray A.
Department of Study
Food Science
Discipline
Food Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Food Science and Technology
Biology, Microbiology
Abstract
This research has involved determining to what extent specific yeast strains typically employed in the food industry, utilize lactose and produce commercially useful by-products. Cheese whey is largely a waste product of the dairy industry which contains approximately 5% lactose, and its untreated disposal contributes a massive biological oxygen demand on municipal sewage treatment plants.
A variety of yeast strains were analyzed for their abilities to achieve the above objectives, and to characterize their growth under experimental conditions, their ability to utilize varied carbon and nitrogen sources, their morphology with electron microscopy, their response to antibiotics, and their DNA ultraviolet absorbance and denaturation curves. A comparison was made of the $\beta$-galactosidase activities of a Candida kefyr isolate (designated as strain K-201), and in different strains of Kluyveromyces fragilis--both of which showed abilities to utilize lactose. The enzyme was found to be constitutive in C. kefyr and inducible in K. fragilis.
Attempts were made, with limited success, to obtain genetically-modified yeasts, by fusion processes and by transformation, to show greater activity in either lactose utilization or in by-product formation. While the techniques used were proven feasible, it was concluded that the pre-existing strain of K. fragilis (CBS 397, obtained from The Netherlands) showed the most efficient lactose utilization, and was the best butanediol and glycerol producer.
It was found that K. fragilis CBS 397 was a nonhalophilic yeast which only produced high glycerol levels when grown under anaerobic conditions, and optimum yields of glycerol only occurred in the presence of 1% Na$\sb2$SO$\sb3$ as a steering agent. The use of other concentrations of Na$\sb2$SO$\sb3$, as well as the use of 5% NaCl or 1% ascorbic acid had no, or even detrimental, effects on cell growth, lactose utilization and glycerol production. Also, glycerol yields were greater in cultures grown from a light inoculum of K. fragilis rather than from resuspended cell masses. Optimally, lactose from the medium was effectively degraded after 45 hour post-inoculation, and glycerol yields of 25% were obtained.
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