PubMed Health⌕ Search

Biomedical subjects

M R Johns

Publications and source records attributed to M R Johns.

7 recordsLinked to original sources
PubMed1999

Solid-state fermentation in rotating drum bioreactors: operating variables affect performance through their effects on transport phenomena.

Aspergillus oryzae ACM 4996 was grown on an artificial gel-based substrate and on steamed wheat bran during solid-state fermentations in 18.7 L rotating drum bioreactors. For gel fermentations fungal growth decreased as rotational speed increased, presumably due to increased shear. For wheat bran fermentations fungal growth improved under agitated compared to static culture conditions, due to superior heat and mass transfer. We conclude that the effects of operational variables on the performance of SSF bioreactors are mediated by their effects on transport phenomena such as mixing, shear, heat transfer, and mass transfer within the substrate bed. In addition, the substrate characteristics affect the need for and the rates of these transport processes. Different transport phenomena may be rate limiting with different substrates. This work improves understanding of the effects of bioreactor operation on SSF performance.

Aspergillus oryzae↗
PubMed1998

Areas of convergence and discordance between the MMPI-168 and the Reiss Screen for Maladaptive Behavior in mentally retarded clients.

The Reiss Screen for Maladaptive Behavior and a modified version of the MMPI-168 were administered to 65 residents of a state mental institution diagnosed with mild or moderate mental retardation. Possible associations between the two screening instruments were then examined. Significant correlations were obtained between four scales of the Reiss Screen and Scales F, K, 1, 6, and 7 of the MMPI-168. These results support the clinical efficacy of both instruments in screening for behavioral pathology in mentally retarded persons. However, some scales purported to assess similar psychological constructs failed to show expected positive associations.

Adolescent↗
PubMed1991

Recovery and purification of polysaccharides from microbial broth.

Current industrial practice to recover extracellular microbial polysaccharides from the broth usually requires dilution to permit cell removal followed by precipitation, typically using alcohol. This paper presents a discussion on the solvent precipitation of xanthan and the results of research performed to investigate the behaviour of xanthan solutions during membrane processing using a microporous membrane. Using crossflow microfiltration, flux rates of up to 120 L/m2h were achieved for pure xanthan solutions, with complete rejection of the polysaccharide by the membrane. The thin film model underpredicted flux for xanthan solutions. In fact, flux was independent of xanthan concentration up to 20-25 g/L, and strongly dependent on crossflow velocity. Considerable benefits in terms of purification and reduced solvent requirements can be obtained by the use of an intermediate crossflow microfiltration step during xanthan recovery.

Bacteria↗
PubMed1990

Hyaluronic acid--a versatile biopolymer.

Since its discovery from bovine synovial fluid, hyaluronic acid has found application in several diverse areas. It is now extensively used in ophthalmic surgery, in the treatment of lameness in racehorses and as an ingredient in cosmetics. It can also be used in drug delivery, orthopedics, cardiovascular aids and in wound healing. Even so, its potential as a therapeutic agent is yet to be fulfilled. New improved products, formed by crosslinking hyaluronic acid with itself or other chemicals, are being produced. Hyaluronic acid is clearly a most valuable therapeutic biopolymer. This article reviews the properties of hyaluronic acid, its biosynthetic pathway and its methods of commercial production, and provides an estimation of its current and future world demand. Experiments designed to improve production economics have been performed in our laboratory. These involved control of glucose and yeast extract concentrations and fermentation pH. Hyaluronic acid production by Streptococcus zooepidemicus was found to be lower at pH 6.5 than at pH 7.1. A new method of extending the production of hyaluronic acid by S. zooepidemicus into the stationary phase has also been achieved.

Biopolymers↗
PubMed1982

Hydrolysis of some natural and synthetic bile acid conjugates by Cercospora melonis.

Analogs of natural bile acid conjugates were incubated with both whole-cell cultures and cell-free extracts of the fungus Cercospora melonis CBS 162.60. Those conjugates containing both an alpha-amino group and a carboxylic acid group in the amino acid moiety were the most susceptible to hydrolysis. Substitution with a beta-amino group and (or) a sulfonic acid group greatly reduced the extent of hydrolysis. With all conjugates tested, significant losses of total bile acid were observed on incubation with whole-cell cultures. Two factors have been implicated as contributing to these losses. First, bile acids may be degraded to nonsteroidal products by an inducible enzyme system. Second, bile acids may be bound to mycelia in a manner not reversed by the extraction technique.

Amino Acids↗
PubMedDate not supplied

A new TEAM in town.

Explore the source record for details and available documents.

Dental Assistants↗