Survival and preservation after freeze-drying process of thermoresistant acetic acid bacteria isolated from tropical products of Subsaharan Africa

in Journal of Food Engineering (2007), 79(4), 1374-1382

Two thermoresistant acetic acid bacteria (TAAB) were previously isolated and selected for a sustainable development of vinegar fermentation in Subsaharan Africa. Their use as a starter culture in vinegar ... [more ▼]

Two thermoresistant acetic acid bacteria (TAAB) were previously isolated and selected for a sustainable development of vinegar fermentation in Subsaharan Africa. Their use as a starter culture in vinegar manufactures in such regions could reduce considerably water cooling expenses. For optimising biomass preservation, the effect of 20% w/w mannitol as cryoprotectant on the cells viability after freeze-drying process and during storage was evaluated. Results showed that freeze-dried cells could be conserved at 4 degrees C for at least 6 months without loss of viability. The main reasons were that cryoprotectant tends to lower the water activity (a(w)) and to maintain a temperature of product weaker than that of the glass transition temperature T-g. Furthermore, the heat resistance of freeze-dried cells during storage was all the more increased that strains were cryoprotected. In addition, intrinsically, an increase of saturated fatty acids with the temperature is the essential modification in the lipidome level of membrane cells when the fermentation occured at a temperature of 30 degrees C. Tolerance to heat during storage was significantly enhanced under such mechanisms. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

Effect of Temperature on Growth of Psychrophilic and Psychrotrophic Members of Rhodotorula Aurantiaca

in Applied Biochemistry and Biotechnology (2000), 84-86(Spring), 391-9

The thermo-dependence of growth kinetic parameters was investigated for the Antarctic psychrophilic strain Rhodotorula aurantiaca and a psychrotrophic strain of the same species isolated in Belgium ... [more ▼]

The thermo-dependence of growth kinetic parameters was investigated for the Antarctic psychrophilic strain Rhodotorula aurantiaca and a psychrotrophic strain of the same species isolated in Belgium (Ardennes area). Cell production, maximum growth rate (mu max), and half-saturation constant for glucose uptake (Ks) of both yeasts were temperature dependent. For the two yeasts, a maximum cell production was observed at about 0 degree C, and cell production decreased when temperature increased. The mu max values for both strains increased with temperature up to a maximum of 10 degrees C for the psychrophilic strain and 17 degrees C for the psychrotrophic strain. For both yeasts, Ks for glucose was relatively constant at low temperatures. It increased at temperatures above 10 degrees C for the psychrophilic strain and 17 degrees C for the psychrotrophic strain. Although its glucose affinity was lower, the psychrotrophic strain grew more rapidly than the psychrophilic one. The difference in growth rate and substrate affinity was related to the origin of the strain and the adaptation strategy of R. aurantiaca to environmental conditions. [less ▲]