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 Title: Fermentation of whey permeate to lactic acid in high cell density bioreactors Author(s): Tejayadi, Susy Doctoral Committee Chair(s): Witter, Lloyd D. Department / Program: Food Science and Human Nutrition Discipline: Food Science Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Agriculture, Food Science and Technology Abstract: Cheese whey permeate poses a severe pollution problem because of its high biological oxygen demand. Since it contains mostly lactose, it can be a valuable source for the production of lactic acid. The objective of this research was to develop a process for the conversion of whey permeate into lactic acid and to design a continuous high-rate fermentation system for this purpose.Batch fermentation studies with L. bulgaricus revealed that pH 5.6 was optimum for lactic acid production whereas pH 6.3 was optimum for growth. Higher substrate (lactose) concentration resulted in longer fermentation time, lower specific productivity and lower specific sugar usage. Increasing the cell concentration at fixed levels of pH and substrate resulted in a shorter fermentation time but a lower specific productivity.The limiting step appears to be utilization of the individual monosaccharides resulting from the hydrolysis of lactose. A diauxic fermentation was observed, in that glucose was consumed first and galactose was not completely consumed even after glucose has been completely consumed.A cell-recycle bioreactor utilizing synthetic membranes was developed as the high-rate fermentation system. With polysulfone hollow fibers, concentration polarization and fouling were the limiting factors with the fermentation broth. Flux increased with pressure at the lower pressures, but became asymptotic at higher pressures. Higher flow rates increased flux, but pH appeared to have little effect on flux.The membrane recycle bioreactor (MRB) was optimized for cell concentration, substrate concentration and dilution rate with respect to two points of commercial interest: maximum productivity and maximum substrate utilization. Overall, the best performance was obtained at a cell concentration of 40 g/L and an initial substrate concentration of 100 g/L; essentially complete substrate utilization was obtained at a dilution rate of 0.25 h$\sp{-1}$, resulting in a lactic acid concentration of 89 g/L. In long term operation, the MRB was stable, requiring a bleed rate of the cells at a rate equal to their growth rate.An economic analysis of the MRB system indicated that the single most important design criterion was the lactate concentration. Yeast extract and permeate transportation cost accounted for up to 73% of the production cost, while the membranes accounted for less than 3%. Issue Date: 1990 Type: Text Language: English URI: http://hdl.handle.net/2142/21174 Rights Information: Copyright 1990 Tejayadi, Susy Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9026333 OCLC Identifier: (UMI)AAI9026333
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