Article

Structure and sucrose hydrolysis activity of Saccharomyces cerevisiae aggregates.

G.B.S.A., Laboratoire de Microbiologie Industrielle, Université Montpellier II, 34095 Montpellier Cedex 5, France.
Biotechnology and Bioengineering (Impact Factor: 4.16). 08/1992; 40(4):475-82. DOI: 10.1002/bit.260400405
Source: PubMed

ABSTRACT The sucrose hydrolysis activity of dense spherical yeast flocs, cultivated on a sucrose medium in a continuous reactor with internal settler, is nearly proportional to the particle surface. From computer simulation, in good agreement with experimental determinations, the calculated sucrose penetration depth is in the range 0.2-0.3 mm, a dimension smaller than the usual diameter of strongly flocculating yeast particles. From specific gravity determinations, the flocs can be considered as homogeneous and cannot exhibit a fractal structure, reported in the literature for a number of microbial aggregates. However, the analysis of the sucrose hydrolysis rates reveals that the cell density may be lower in the outer layer of the flocs.

0 Bookmarks
 · 
61 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Alcohol fermentation productivity can be strongly improved using a flocculation-based yeast recycle. However, the efficiency of the biomass retention system depends strongly on the yeast particle size. Accordingly, the monitoring and control of yeast floc diameter are of primary importance. The on-line measurement of mean floc diameter has been achieved using on-line image analysis, based on the evaluation of image texture. The texture analysis method consisted in the building of a co-occurrence matrix from which the so-called “Energy parameter” was extracted. While image texture is usually used for classification purposes, it has been used here as a quantitative descriptor: a correlation has been found between this statistical image feature and off-line manual floc-size determinations. In the floc-size range investigated (|bu 0.5–4.3 mm), the evaluated mean diameter was in good agreement with the actual particle size, with a determination coefficient equal to 0.980. In contrast with manual measurements, slow and tedious, this method gave the value of the mean particle diameter in real-time, without sampling. This novel tool has been used to investigate the behavior of yeast aggregates as a function of fermentation conditions. While biomass concentration was kept constant, step increases of the feed rate led to a decrease of the mean floc diameter. Image analysis showed that the particle-size reduction could occur within a few minutes after modification of the medium dilution rate, demonstrating the disruptive effect of the CO2 efflux. The kinetic of aggregate formation was dependent on the gas-phase composition. Instead of recycling fermentation gas, sparging the fermentor with nitrogen, to reduce dissolved CO2 concentration, increased the rate of floc-size growth. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 76: 91–98, 2001.
    Biotechnology and Bioengineering 08/2001; 76(2):91 - 98. · 4.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this work was to identify the main viable heterotrophic bacteria in a marine fish farm with a recirculating water system and to study their growth dynamics. The experiments were performed with sea bass (Dicentrarchus labrax) in an experimental recirculating water system. The bacteria identified were typical of the marine environment: Pseudomonas, Oceanospirillum, Marinobacter, Paracoccus and Erythrobacter genus from Bergey’s group IV, two genus of Vibrionaceae, one strain of Vibrio and one strain of Aeromonas. These populations were stable when the ingested feed/replacement water ratio was kept constant. Fixed bacteria formed large biofilms, which released about 104 CFU ml−1 into the tank. The biological filter, with its large surface area, was the largest source of bacteria in the farm, but the UV disinfection unit kept the number of free bacteria stable. When properly managed, the majority of bacteria that grew on the biological filter were from Bergey’s group IV; no Vibrio were ever detected on it.
    Aquacultural Engineering. 01/2000;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The hydraulic model of a gas lift bioreactor, during a continuous alcoholic fermentation by using a strongly flocculating yeast, is analysed. Sucrose at two different concentrations (50 and 100 g/l) was used as substrate and the dilution rate for all the experiments was 1 h–1. The biomass concentrations were between 85 and 110 g dry weight/1. A stimulus response technique was used to obtain the Residence Time Distribution curves, a pulse of a lactose solution being used as the tracer. Mixing time was determined by means of the response to a pulse of an acid tracer. These experiments were carried out by using an on-line data-acquisition system. The bioreactor behaviour is completely homogeneous, except for high substrate and biomass concentrations. A two parameters combined model is necessary, in this case, to fit the experimental data. Mixing times are very low, in the order of 10 seconds.
    Bioprocess and Biosystems Engineering 01/1995; 12(5):269-272. · 1.87 Impact Factor