Biomedical subjects

P B Conrad

Publications and source records attributed to P B Conrad.

3 recordsLinked to original sources

PubMed2000

Stabilization and preservation of Lactobacillus acidophilus in saccharide matrices.

Lyophilization and vacuum- or spray-drying are some of the most useful techniques for preserving foods, agricultural products, and pharmaceuticals. Biological materials, however, can be irreversibly damaged during these treatments. Therefore, it is essential to design protective agents to preserve protein activity and cell viability. In this paper we examine the use of alpha, alpha-trehalose-borate systems as protectants for Lactobacillus acidophilus during freeze- and vacuum-drying. Trehalose was found to be an effective protectant for freeze-dried and vacuum-dried samples, and it is equivalent to a protective formulation which is in current industrial use. It is known from our previous work on enzymes that the presence of borate can dramatically enhance the protective ability of trehalose. In this work, the addition of trehalose-borate to bacterial concentrate greatly improves the recovery of viable cells after storage. This improvement was seen in freeze-dried samples stored at 37 degrees C as well as for vacuum-dried samples held at room temperature. A tailored buffering strategy was tested to counteract the high pH resulting from the addition of borate to the mixture. Use of citric or lactic acids in combination with ammonium hydroxide gave a protectant solution with high pH (resulting in effective crosslinking between trehalose and borate) but a dry product with reduced pH upon rehydration (conducive to cell survival). These results raise exciting possibilities for protection of more labile prokaryotic species as well as simple eukaryotes.

Ammonium Hydroxide↗

PubMed1998

Two-phase bioconversion product recovery by microfiltration I. Steady state studies.

Recovery of an aqueous bioconversion product from complex, two-phase Pseudomonas putida broths containing 20% (v/v) soybean oil presents a significant challenge for downstream processing. Although not used before in multiple-phase separation for complex biotech products, crossflow filtration employing ceramic filters is one of the most attractive options which allow the design of integrated, continuous bioconversion processes. As a first attempt, we studied multichannel, monolithic ceramic membranes of different nominal pore sizes and lumen diameters under steady-state conditions. The best performance was obtained with 0.2-microm-pore/3-mm-lumen membrane, which completely rejected both cells and oil droplets from the permeate, creating a clear aqueous product stream. Although the same separation was achieved, the 50K molecular weight cut-off (MWCO) ultrafilter showed greater irreversible but similar reversible resistance, in addition to an order-of-magnitude higher membrane resistance. Larger nominal pore microfilters, such as 0.45 and 1.0 microm, experienced both cell and oil leakage even at low transmembrane pressure (10 psig). Attributed to greater shear at the same recirculation rate, smaller lumen filters did provide greater permeate flux. However, for practical purposes, the 0. 2-microm-pore/4-mm-lumen ceramic membrane was chosen for further evaluation. Transmembrane pressures up to 50 psig provided only marginal gains in filtration performance, whereas increasing shear rate resulted in linear increases in steady-state flux, presumably due to formation of shear-sensitive, complex gel/oil/cell layer near the membrane surface. A nominal shear rate of 9200 s-1 and 20 psig transmembrane pressure were chosen as optimal operating conditions. Additional studies in a clean system revealed that as low as 5% (v/v) soybean oil in deionized (DI) water resulted in an order-of-magnitude decline in steady-state permeate flux. Breakthrough of oil droplets occurred at 35 psig transmembrane pressure. The severe fouling and breakthrough phenomena disappeared in the presence of washed cells for transmembrane pressure up to 43 psig, implying an oil/cell layer coating the membrane surface, thus preventing oil penetration. Serious membrane fouling was also experienced in microfiltration of oil-free, cell-free supernatant and oil-free whole broth. Consequently, soluble proteins/surfactants were suspected to be the major membrane foulants. Interestingly, soybean oil up to 30% (v/v) enhanced the flux, presumably through complicated interactions with the major foulants. Regeneration of membrane was best achieved with protease and hot caustic/bleach treatments, supporting the hypothesized fouling mechanisms mentioned above. This work provides process and system information for batch microfiltration runs in the future, to be reported elsewhere as Part II of this work.

Adsorption↗

PubMed1989

Transport of N-acetyl-D-glucosamine and N-acetyl-D-galactosamine by rat liver lysosomes.

Transport of N-acetyl-D-glucosamine and N-acetyl-D-galactosamine, products of lysosomal glycoprotein and glycosaminoglycan degradation, was examined in Percoll gradient purified rat liver lysosomes. Uptake of these two sugars was competitive and quite specific remaining largely unaffected by the presence of L-fucose, D-glucosamine, D-glucose, D-glucuronic acid, D-mannose, or N-acetylneuraminic acid. Kinetic studies revealed a Km of 4.4 mM for both N-acetyl-D-glucosamine and N-acetyl-D-galactosamine uptake. Temperature dependence studies revealed a Q10 of 2.3. N-Acetyl-D-glucosamine uptake was not dependent upon NaCl, KCl, MgCl2, or ATP/MgCl2 and was unaffected by 5 mM dithiothreitol or variation of buffer pH between 6.0 and 8.0. Cytochalasin B at a concentration of 50 microM effectively inhibited uptake of N-acetyl-D-glucosamine by 90% and N-acetyl-D-galactosamine by 65%. Prior incubation of lysosomes in 20 mM N-acetyl-D-glucosamine stimulated uptake of both sugars 3-4-fold, although it had no effect on the uptake of D-glucose. Countertransport was unaffected by neutral and cationic amino acids demonstrating independence from these amino acid transport systems. We conclude that lysosomes possess a highly specific transport system for N-acetyl-D-glucosamine and N-acetyl-D-galactosamine.

Acetylgalactosamine↗