Lactic acid fermentations were performed with plastic-composite-support (PCS) disks in solvent-saturated media with Lactobacillus casei subsp. rhamnosus (ATCC 11443). The PCS disks contained 50% (w/w) polypropylene, 35% (w/w) ground soybean hulls, 5% (w/w) yeast extract, 5% (w/w) soybean flour, and 5% (w/w) bovine albumin. Bioassays were performed by growing L. casei in solvent-saturated media after soaking the PCS disks. Eighteen different solvent and carrier combinations were evaluated. Overall, L. casei biofilm fermentation demonstrated the same lactic acid production in solvent-saturated medium as suspended cells in medium without solvents (control). To evaluate PCS solvent-detoxifying properties, two bioassays were developed. When solvent-saturated medium in consecutive equal volumes (10 mL then 10 mL) was exposed to PCS, both media demonstrated lactic acid fermentation equal to the control. However, when solvent-saturated medium with two consecutive unequal volumes (10 mL then 90 mL) was exposed to PCS, some degree of toxicity was observed. Furthermore, iso-octane, tributylphosphate (TBP), and Span 80 were optimized for recovery as 91%, 5%, and 4% (v/v), respectively, with a 1:1 ratio of 1.2 M Na(2)CO(3) stripping solution. Also, recovery by emulsion liquid extraction in the hollow-fiber contactor was minimal due to low recovery at pH 5.0 and incompatibility of the solvent and hollow-fiber material. These results suggest that PCS biofilm reactors can benefit lactic acid fermentation by eliminating the toxic effect from solvent leakage into the fermentation medium from liquid-liquid extractive integrated fermentations.

An immobilized-cell biofilm reactor was used for the continuous production of lactic acid by Lactobacillus casei subsp. rhamnosus (ATCC 11443). At Iowa State University, a unique plastic composite support (PCS) that stimulates biofilm formation has been developed. The optimized PCS blend for Lactobacillus contains 50% (wt/wt) agricultural products [35% (wt/wt) ground soy hulls, 5% (wt/wt) soy flour, 5% (wt/wt) yeast extract, 5% (wt/wt) dried bovine albumin, and mineral salts] and 50% (wt/wt) polypropylene (PP) produced by high-temperature extrusion. The PCS tubes have a wall thickness of 3.5 mm, outer diameter of 10.5 mm, and were cut into 10-cm lengths. Six PCS tubes, three rows of two parallel tubes, were bound in a grid fashion to the agitator shaft of a 1.2-1 vessel for a New Brunswick Bioflo 3000 fermentor. PCS stimulates biofilm formation, supplies nutrients to attached and suspended cells, and increases lactic acid production. Biofilm thickness on the PCS tubes was controlled by the agitation speed. The PCS biofilm reactor and PP control reactor achieved optimal average production rates of 9.0 and 5.8 g l(-1) h(-1), respectively, at 0.4 h(-1) dilution rate and 125-rpm agitation with yields of approximately 70%.

Introduction Materials and Methods Results and Discussion Conclusions Acknowledgments References GENERAL CONCLUSIONS ACKNOWLEDGMENTS The first paper demonstrates the effectiveness ofcontinuous.,lacti-e-aeid fermentation using PCS tubes-fixed to the agitator shaft for cell immobilization via• biofilm reactor•. The second paper studies the effect of carrier concentration, surfactant concentration, and stripping solution concentration on lactic acid recovery to optimize the emulsion composition using selected solvents and carriers with a minimal and high toxic effect on Lactobacillus casei. The effect of external aqueous phase pH on emulsion liquid membrane extraction is reported. Lactic acid recovery via emulsion liquid extraction in a hollow fiber contactor with a toxic solvent combination is also evaluated. Thesis Organization ' ,. This thesis follows an alternative format and is divided into two papers. Each paper contains an abstract, introduction, materials and methods, results and discussion, conclusions, acknowledgments, and references with tables and figures included in the text. The papers are written to conform to the specifications of Applied and Environmental Microbiology, the journal to which the papers will be submitted. A general introduction chapter including a literature review and general conclusion chapter have been included. All experiments, data collection, and data analysis were performed by the candidate. Literature Review Lactic Acid Lactic acid (2-hydroxypropionic acid) is found widely throughout nature in two isomeric forms. In mammalian systems, lactic acid occurs in the L(+) isomer. Both L(+) and D(-) enantiomers exist in bacterial systems. Lactic acid can be made by fermentation or by chemical synthesis. It is also a major metabolite intermediate in many living organisms (56). Applications of Lactic Acid Lactic acid has two major application classes. The first class being food, medicine and cosmetic industries. Secondly, lactic acid is used as a chemical for chemistry and technology. Lactic acid that is commercially purchased is one of three grades: technical, food, and pharmaceutical. Lactate salts, such as calcium lactate, are also available. Technical grade lactic acid was traditionally used by the tanning industry for deliming hides. It is also used in the textile industry as mordant for color prints (32). The food and food-related applications constitute 85% (wt/vol) of the demand for lactic acid in the United States (10, 40). Lactic acid a11-d calcium lactate as food additives are considered "generally recognized as safe" (GRAS) by the Food and Drug Administration (FDA). Lactic acid is also a "natural" ingredient in many foods. Lactate salts are soluble, and lactic acid is easily applicable as a liquid (32). As a preservative, lactic acid displays bacteriostatic properties (3). Food grade lactic acid, also referred to as edible grade, is used as an acidulent and preservative. It has many advantages over other acids used in food systems.

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