Thesis (M.S.)--University of Wisconsin, 1944. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. 20-22).

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Typescript. Abstracted in Dissertation abstracts, v. 20 (1959) no. 2, p. 486. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 107-111).

Thesis (M.S.)--University of Wisconsin--Madison, 1940. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Akademisk avhandling--Lund., 1937. / At head of title: From the Physiological institute and the Ophthalmiatric clinic, University of Lund, Sweden. Translated by Bert Hood. Imprint on cover: Copenhagen, Levin & Munksgaard, 1937. Bibliography: p. [267]-279.

Recent data on the effect of trace elements on the production of citric acid by Aspergillus niger 72-4 suggested that at last a firm basis had been established for studies on the mechanism of production. Citric acid production is an important commercial process and most research had been directed toward obtaining high yields of the acid. The small amount of information on mechanisms is invalidated by the new knowledge of the importance of trace minerals in citric acid synthesis. The attempt at elucidating a system was approached by studying the distribution of organic phosphates in the mats and by manometric experiments. By using the Umbreit fractionation method combined with chromatographic analysis none of the phosphorylated intermediates present in the Embden-Meyerhof system could be identified. Evidence for a pentose and a ketose phosphate is presented. The manometric studies on still cultures were unsatisfactory due to a high endogenous rate and to difficulties in handling the mat. Shake cultures grown for four days and then depleted for 24 hours in the medium minus sucrose and manganese were shown to be a workable method for manometric studies. Using this method evidence for the presence of most of the enzymes required for the oxidation of the Krebs cycle intermediates is presented. A survey of the literature on cell preparations was made. Attempts to prepare active cell preparations failed since enzyme activity seems to be associated with the structural integrity of the mycelium. / Land and Food Systems, Faculty of / Graduate

Among the various fungal strains screened for citric acid production, Aspergillus niger is known to produce considerable amounts of citric acid and other organic acids when cultivated in carbohydrate-rich medium in solid substrate fermentation (SSF). Since A. niger on a solid substrate grows under conditions similar to the natural habitat, SSF is ideal to cultivate A. niger for the purpose of producing citric acid. / An initial optimization (study 1) was conducted in batch type fermentation experiments using peat moss supplemented with glucose to simulate an organic waste. The effects of various nutrients (glucose, (NH4)2SO 4, KH2PO4 and NaCl), fermentation parameters (moisture content, temperature, inoculum density, composition of solid substrate and particle size) and of initial level of potential stimulators (ethanol, methanol, phytate and surfactant) were evaluated with respect to citric acid production by A. niger grown on damp peat moss. In these experiments, optimization using a traditional 'one-factor-at-a-time' method was applied to determine key factor ranges for the production of citric acid. When the fermentation was carried out using the final optimal conditions. This allowed for a 50-fold increase in citric acid production compared to the production of citric acid by A. niger grown on peat moss supplemented with 100 g glucose/kg DPM. / A second set of experiments (study 2) was conducted to optimize fermentation conditions for citric acid production in a column bioreactor. A. niger NRRL 567 grown on damp peat moss was held within a column bioreactor and periodically irrigated with a glucose-rich solution simulating field conditions. Three variables including aeration, thickness of solid substrate bed and incubation temperature were optimized using a 23 full factorial design (FFD). Under optimum, the total citric acid production and yield were 120.6 g/kg DPM and 18.5% respectively. / A third experiment (study 3) compared the production of citric acid by A. niger in submerged fermentation using cheese whey, as opposed to batch and semi-continuous fermentation using peat moss. Various fermentation conditions such as nutrients (glucose, (NH4)2SO 4 and KH2PO4), stimulators (methanol, olive oil and phytate) and fermentation parameters (pH, fermentation time and inoculum density) were optimized using a central composite design (CCD). Citric acid production improved citric acid production by a factor of 13.3 when compared to the production of citric acid by A. niger NRRL 567 using whey-based medium (50 g/l) alone. / As compared to submerged and semi-continuous fermentation, Batch type SSF could take higher levels of initial glucose and produce the high concentration of citric acid within a shorter period of time. Thus, SSF may be considered to be better technique than submerged fermentation, if main disadvantage like non-homogeneous fermentation conditions could be overcome.

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