## LSU Historical Dissertations and Theses

1988

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

School of Nutrition and Food Sciences

Donal F. Day

#### Abstract

Dextranase is an enzyme which destroys dextran, a contaminant in sugar and a main constituent of dental plaque. Dextranase utilization can solve a major economic problem in the sugar industry, and in dental preparations it can keep teeth essentially free of plaque. The dextranase from the yeast Lipomyces starkeyi was investigated because this organism has been used in food related processes. This attribute should allow for Food and Drug Administration (FDA) approval for use of a Lipomyces dextranase. None of the existing commercial dextranase preparations have FDA approval. L. starkeyi was found to produce maximum amounts of dextranase when grown in a minimal medium at pH 3.0. A derepressed mutant was selected and the optimum conditions for induction of dextranase production were determined. $\beta$-Methyl-glucopyranoside was found to be a gratuitous inducer of dextranase synthesis. A fermentation system was scaled up to pilot scale and the enzyme was purified and characterized with respect to both its physical and kinetic parameters. The dextranase produced by L. starkeyi was found to be catalytically similar to the dextranases from Penicillium and Chaetomium. Dextranase from L. starkeyi was used to treat stale cane juice. A 76% reduction in dextran content, by the Haze method, was seen in the final sugar product.

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