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R D Tanner

Publications and source records attributed to R D Tanner.

24 records · Page 2Linked to original sources
PubMed1981

Inherent limitations to the problem of reducing the lysine microbiological assay time.

A kinetic approach is proposed to shorten the microbiological assay time for the determination of unbound L-lysine. The present lysine bacterial assay takes from 16 to 24 h using Pediococcus cerevisiae P-60 ATCC 8042 (formerly Leuconostoc mesenteroides P-60 ATCC 8042) and uses a medium in which lysine is the limiting substance. Measurements of the final cell concentration are linearly correlated with the initial concentration of lysine, S, to provide an indirect estimate of S. We propose to understand the limitations inherent to the reduction of the assay time to 4 h by focusing in our analysis on the bacterial late lag or early growth transient phases, rather than the stationary phase of growth. Generally, the Monod equation is expected to describe a hyperbolically increasing correlation between the bacterial specific growth rate at about 2-4 h and the initial lysine concentration. A hyperbolic correlation is obtained by 3 h, but the lysine region of interest falls in the saturated portion of the curve. Discriminations between different initial lysine levels are therefore difficult with this nearly flat curve. On the other hand, when the initial inoculum level is lowered, so that substrate inhibition becomes effective, a correlation with a large negative slope is obtained by 4 h. Limitations to using absorbance measurements for the rapid assay turn up in a lack of reproducibility and, hence, a large variance associated with the measurements. Alternative microbial measuring techniques, such as impedance methods, need to be examined in order to reduce that large variance.

Biological Assay↗
PubMed1977

A fermentation process for producing both ethanol and lysine-enriched yeast.

In 18 batch-fermentation experiments, baker's yeast was grown in an enriched mineral medium, containing 10% by weight glucose, at various pH and temperature levels. The pH and temperature are just two representative engineering variables which can be easily varied at negligible cost. The commercial yeast inoculum, 20% by weight or about .16% viable cells, was selected to represent industrial (nonsterile) conditions. Free L-lysine, ethanol, and cell growth were followed in time for each batch run held at a fixed pH and temperature. The maximum free lysine level reached at either 10 1/2 or 24 hr occurred at a pH of 5 and 32 degrees C. At 24 hr, the peak free lysine level, 120 mg/liter, is three times as great as the uncontrolled pH counterpart. In terms of total L-lysine (free plus protein-bound) the peak represents a 25% improvement over the uncontrolled case, based on an average 3.5% lysine level per cell weight. The greatest measured cell level, .9% by weight in the fermentation broth, or a 5 1/2-fold increase over th inoculum, was reached during the 36 degrees C and pH 3 run, while the largest measured ethanol value (3%, or 30% conversion by weight from glucose) was achieved during the 28 degrees C and pH 6 experiment. The optimal lysine run product, however, no less than 15% of the maximum cell and 30% of the maximum ethanol levels.

Ethanol↗
PubMedDate not supplied

In situ bubble fractionation strategies for separating individual proteins in a batch baker's yeast fermentation process.

Extracellular proteins produced by yeast have been observed to stratify in the extracellular fluid of a batch bioreactor, thus creating a vertical concentration gradient. We observed that, in the four different experiments conducted, each varied in their protein recovery characteristics. For example, sparging the system with gas accentuates the separation, though even in a nonsparged system, the in situ generation of minute carbon dioxide bubbles by yeast cells creates a protein gradient as the bubbles carry proteins upward. Based on these and other observations, we propose possible strategies for recovering the individual proteins from a system containing the four major proteins considered. A simple steady-state mathematical model, based on convective upward protein transport being balanced by downward protein diffusion, has been used to describe the behavior of each of these four extracellular proteins in the fermentation broth.

Fermentation↗