The States of Water in Model Food Systems and Their Effect on Staphylococcus aureus at Intermediate Water Activity.
Abstract
A mass balance was developed to calculate moisture content of a model formulation giving the desired water activity (aw) over 0.33 to 0.95. A model was derived to obtain aw of a mixture from total moisture content and ingredient isotherms. A model was developed to calculate energy of water binding by a mixture of ingredients. Polymers and solutes show greatly different Smith plots. Pulsed NMR studies showed T1 relaxation times were negligible for polymer water and large for solute water. At 0.91 aw, only solute water allowed ascorbic acid oxidation. Similarly, Aspergillus parasiticus conidia germinated only in solute water. The mechanism by which S. aureus was able to grow at high osmotic strenght was investigated with the aid of a salt-sensitive mutant. Analysis of the free intracellular amino acid pool showed that its size and composition changed drastically when the bacterium was challenged with salt. Glutamine accumultated. Proline was found to be important to osmoregulation. It is not synthesized in response to challenge but the increase is the result of transport. Thus, S. aureus is sensitive to NaCl when exogenous proline is not available. This transport is mediated by three permeases. Proline oxidase activity decreased with decreasing aw. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1982
- Accession Number
- ADA121786
Entities
People
- L. S. Witter
- Marvin P. Steinberg
Organizations
- University of Illinois Urbana–Champaign