Lactate + CO 2. Malate. Modeling Biomass Production. Cell density ( X , g/L) changes over time at a rate proportional to the current cell density. O. oeni. Mathematically this is represented as:. Biomass Production of the Bacteria Oenococcus oeni.
Modeling Biomass Production
Cell density (X, g/L) changes over time at a rate proportional to the current cell density.
Mathematically this is represented as:
Biomass Production of the Bacteria Oenococcus oeni
where μ represents the specific growth rate. During exponential growth the specific growth rate reaches its maximum and remains constant at μ = μmax.
Biomass Production Process
Ashton, R., Juenke, C., Kennedy, B., and Leitschuh, J., School of CBEE
Commercial biomass production of the bacteria OenococcusOeni (a bacteria that performs malolactic acid fermentation in wine) is currently inefficient and expensive. The growth, processing and packaging of O.oeni will be optimized in order to create a cost effective strategy for biomass production.
O. oeni biomass is grown to its maximum cell density in a bioreactor. The cell broth is then concentrated by centrifugation. Prior to freeze-drying the concentrated cells are exposed to pre freeze-drying treatments such as cryoprotectants. The cells are then freeze-dried for packaging and storage.
Therefore, during exponential growth:
The specific growth rate is effected by a number of factors including temperature, pH, dissolved oxygen and growth media composition. Optimization of μmaxis integral to optimizing biomass production.
Oenococcusoeni is an important bacterial species used for malo-lactic (ML) fermentation in the wine industry. ML fermentation is a secondary fermentation in wine in which malic acid (a naturally occurring acid in grapes) is converted to lactic acid, and occurs after the primary alcoholic fermentation performed by yeast. It improves wine quality by reducing the total acidity, thereby softening the wine. In addition, it infuses a favorable buttery aroma from an intermediate of ML fermentation called diacetyl.
Industry Production Scale-Up
Electron microscopy image of the bacteria Oenococcus oeni (~1 μm), which is used to reduce tartness in wine by converting malic acid from grapes to a softer tasting lactic acid .
The Oregon market calls for 1000 lb of bacteria per year. Using growth parameters determined in a 3L bioreactor (left), nine 1000L bioreactors would be required to meet this demand. The scaled-up design (right, not to scale) takes into account freeboard space, a conical bottom of height, Hcone, and a height, Htotal, to diameter, D, ratio of 2 (a general heuristic for bacterial bioreactors).
A typical growth curve for a bacterial culture in a bioreactor.
Biomass Production Results
Oenococcus oeni was grown in a 3L lab-scale bioreactor containing the rich medium Luria Broth at pH 4.0 and 25°C (optimum values determined from literature) under both batch and fed-batch conditions. Fed-batch operations did not appear to effect the maximum cell density.
O. oeni performs ML fermentation in wine production, reducing tartness by converting malate (malic acid) in grapes to lactate (lactic acid) and giving the wine a “buttery” flavor and aroma , .
Process flow diagram for the biomass production of Oenococcus oeni.
Lab scale bioreactor.
Scale-up bioreactor design.
Fed batch started here. It did not significantly increase growth.
Htotal = 1.8 m
Hcone = 0.5 m
Extended lag phase due to refrigeration of cells prior to inoculation.
Downstream Processing and Packaging
D = 0.9 m
The effect of lyophilization (freeze-drying) in varying sucrose solutions on cell viability is currently being investigated. Lyophilization is being considered for production scale storage and packaging.
The growth curves for O. oeni. Inoculum for the fed-batch run had been previously refrigerated which caused the extended lag phase.
 Yarris, L. (n.d.). Science Beat. Secrets of the wine cellar: the genome of a wine-making microbe . Retrieved March 2, 2010, from Berkely Lab: http://www.lbl.gov/Science-Articles/Archive/JGI-wine-making-genome.html
 African Trading Company. http://www.africantradingco.com/winebarrels.html
 Feast NH. http://blogs.nashuatelegraph.com/livefreeordine/2009/04/
Analysis of growth curves from O. oeni yielded:
which correlates to the highest specific growth rate for this organism found in literature. Maximum cell densities occurred around 1.7-1.9 g/L. This appeared to be independent of substrate levels as indicated by the fed-batch operation. These values are also verified by literature as being high yields for O oeni.
Vacuum pump attached to the Lyo-centre lyophilizer.
Lyo-centre vacuum chamber and vacuum flask.