Time series analysis of aerobic bacterial flora during Miso fermentation

AIMS: This article reports a microbiological study of aerobic mesophilic bacteria that are present during the fermentation process of Miso. METHODS AND RESULTS: Aerobic bacteria were enumerated and isolated from Miso during fermentation and divided into nine groups using traditional phenotypic tests. The strains were identified by biochemical analysis and 16S rRNA sequence analysis. They were identified as Bacillus subtilis, B. amyloliquefaciens, Kocuria kristinae, Staphylococcus gallinarum and S. kloosii. All strains were sensitive to the bacteriocins produced by the lactic acid bacteria isolated from Miso. CONCLUSIONS: The dominant species among the undesirable species throughout the fermentation process were B. subtilis and B. amyloliquefaciens. It is suggested that bacteriocin-producing lactic acid bacteria are effective in the growth prevention of aerobic bacteria in Miso. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has provided useful information for controlling of bacterial flora during Miso fermentation.     

Yeast and pesticide interaction during aerobic fermentation

Summary The action of a yeast (Saccharomyces cerevisiae) upon the insecticides Carbaryl, Tetrachlorvinphos and Deltamethrin and the fungicides Quinomethionate, Triadimefon and Vinclozolin during aerobic fermentation was investigated. The yeast adsorbed all the pesticides, four of them completely and two (Carbaryl, 50%, and Triadimefon, 90%) partially. In the case of Deltamethrin and Quinomethionate, degradation also occurred.     

Turnover characteristics in continuous l-lysine fermentation

The turnover characteristics of a microbial bioreactor were comparatively investigated as a closed (batch) and a continuous stirred tank reactor (CSTR) open system, using a 2-l fermentor. Corynebacterium glutamicum (ATCC 21544) was chosen as the microorganism since it has the ability to produce l-lysine. Parameters measured were l-lysine production rates, glucose consumption rates and biomass production rates as a function of dilution rate, bioreactor volume and biomass concentration. The modes of microbial cell behaviour under steady-state and transition-state conditions were examined. Investigations on scaling properties of the CSTR system were also aimed at comparing scaling or allometry of metabolic rates in organisms that are also open energy dissipative systems.This investigation was first presented at the 10th Dechema-Jahrestagung der Biotechnologen, 1–3 June 1992, Karlsruhe, Germany     

Phosphate mediation of the aerobic fermentation in baker's yeast

Summary If the supply of phosphate were restricted in a glucose-limited chemostat culture of baker's yeast to an extent that residual phosphate in the medium could hardly be observed, the value of critical dilution rate was apparently enhanced. This observation suggests a possible mediation by phosphate between anaerobic and aerobic functions of the baker's yeast.     

Modelling of continuous acetonobutylic fermentation

A model of continuous acetonobutylic fermentation is proposed. This model correctly portrays the predominantly solvents formation observed at acidic extracellular pH and predominantly acids production at more neutral pH, as well as observed effects of dilution rate and feed substrate on products' concentrations. A fair agreement between experimental and theoretical predictions is achieved for a broad range of operating variables.     

Xanthan production byXanthomonas campestris in continuous fermentation

Summary Xanthan production by a strain ofX. campestris was maintained longer under glucose—limited than nitrogen—limited conditions in continuous culture. The turnover Q was 12 at lower pH(5.0–6.0) and 6.5 at neutral pH; xanthan productivity was comparable at both pH in nitrogen—limited continuous cultures. In the Fe—rich continuous fermentation cell degeneration did not occur for 65 turnovers whereas in the Fe—deficient fermentation it occurred in 12 turnovers. The culture stability for xanthan formation is higher under conditions which are favorable for cell growth with limited xanthan production.     

Ethanol fermentation in a continuous tower fermentor

A mutant of Saccharomyces cerevisiae, which forms large, multicellular flocs in liquid culture, rapidly fermented media containing high concentrations of glucose (100-180 g/L) in a continuous nonaerated tower fermentor at 30 degrees C. The fermentor operated continuously for seven months. Batch and tower fermentor data were fitted to a kinetic model incorporating linear ethanol inhibition and Monod dependence on glucose. Conversion, ethanol yield, and ethanol productivity were related to the apparent fermentation time for initial glucose concentrations of 130 and 180 g/L. Productivities of 8-12 g ethanol/L h were achieved through the yeast bed giving conversions exceeding 90% of the theoretical yield.     

Adaptive on-line model for aerobic Saccharomyces cerevisiae fermentation

In order to study and control fermentation processes, indirect on-tine measurements and mathematical models can be used. In this article we present a mathematical on-line model for fermentation processes. The model is based on atom and partial mass balances as well as on equations describing the acid-base system. The model is brought into an adaptive form by including transport equations for mass transfer and unstructured expressions for the fermentation kinetics. The state of the process, i.e., the concentrations of biomass, substrate, and products, can be estimated on-line using the balance part of the model completed with measurement equations for the input and output flows of the process. Adaptivity is realized by means of on-line estimation of parameters in the transport and kinetic expressions using recursive regression analysis. These expressions can thus be used in the model as valid equations enabling prediction of the process. This makes model-based automation of the process and testing of the validity of the measurement variables possible. The model and the on-line principles are applied to a 3.5-L laboratory tormentor in which Saccharomyces cerevisiae is cultivated. The experimental results show that the model-based estimation of the state and the predictions of the process correlate closely with high-performance liquid chromatography (HPLC) analyses. (c) 1995 John Wiley & Sons, Inc.     

Steady-state and transient-state analyses of aerobic fermentation in Saccharomyces kluyveri

Some yeasts, such as Saccharomyces cerevisiae, produce ethanol at fully aerobic conditions, whereas other yeasts, such as Kluyveromyces lactis, do not. In this study we investigated the occurrence of aerobic alcoholic fermentation in the petite-negative yeast Saccharomyces kluyveri that is only distantly related to S. cerevisiae. In aerobic glucose-limited continuous cultures of S. kluyveri, two growth regimens were observed: at dilution rates below 0.5 h(-1) the metabolism was purely respiratory, and at dilution rates above 0.5 h(-1) the metabolism was respiro-fermentative. The dilution rate at which the switch in metabolism occurred, i.e. the critical dilution rate, was 66% higher than the typical critical dilution rate of S. cerevisiae. The maximum specific oxygen consumption rate around the critical dilution rate was found to 13.6 mmol (g dry weight)(-1) h(-1) and the capacity of the pyruvate dehydrogenase-bypass pathway was estimated to be high from in vitro enzyme activities; especially the specific activity of acetyl-CoA synthetase was much higher than in S. cerevisiae at all tested conditions. Addition of glucose to respiring cells of S. kluyveri led to ethanol formation after a delay of 20-50 min (depending on culture conditions prior to the pulse), which is in contrast to S. cerevisiae that ferments immediately after glucose addition.     

Nonlinear observation of specific growth rate in aerobic fermentation processes

Simple nonlinear observers for the on-line estimation of the specific growth rate from presently attainable real-time measurements are presented. The proposed observers do not assume or require any model for the specific growth rate and they are very successful in accurately estimating this parameter. Moreover, they are very easy to implement and to calibrate. Indeed, due to the particular structure of their gain, their tuning is reduced to the calibration of a single parameter. Simulation results obtained under different operating conditions are given in order to highlight the performances of the proposed estimators.     

Effect of reducing agents in an aerobic amino acid fermentation

This study focuses on the effects of the reducing agents, dithiothreitol (DTT) and glutathione (GSH), on amino acid production in aerobically growing Corynebacterium glutamicum. The problem of reducing agent addition affecting the dissolved oxygen level was solved by positioning the culture at a high dissolved oxygen level and feeding the reducing agent into the fermentor. We show that it is possible to lower the redox potential even in a highly aerobic environment. The addition of DTT to the fermentation during the growth phase caused a significant increase in specific amino acid production rate and total amino acids produced, as compared with a control. In contrast, GSH had an inhibitory effect. (c) 1992 John Wiley & Sons, Inc.     

Optimal control of continuous fermentation processes

Three layer control structure is proposed for optimal control of continuous fermentation processes. The start-up optimization problems are solved as a first step for optimization layer building. A steady state optimization problem is solved by a decomposition method using prediction principle. A discrete minimum time optimal control problem with state delay is formulated and a decomposition method, based on an augmented Lagrange's function is proposed to solve it. The problem is decomposed in time domain by a new coordinating vector. The obtained algorithms are used for minimum time optimal control calculation of Baker's Yeast fermentation process.List of Symbols x(t) g/l biomass concentration - s(t) g/l limiting substrate concentration - x ⁰ g/l inlet biomass concentration - s ⁰(t) g/l inlet substrate concentration - D(t) h^–1 dilution rate - (t) h^–1 specific growth rate - Y g/g yield coefficient - (t) h^–1 specific limiting substrate consumption rate - k _D h^–1 disappearing constant - w ₁, w ₂ known constant or piece-wise disturbances - _m h^–1 maximum specific growth rate - k _s g/l Michaelis-Menten's parameter - h time delay - x ₀, s ₀ g/l initial concentrations - ¯x, ¯s, ¯D optimal steady state value - V _min , V _max , v=x,s,d,t bounds of variables - t h sampling period - K number of steps in the optimization horison - Js, J _d performance indexes - L _s Lagrange's function - L _d Lagrange's functional - ₀ weighting coefficient for the amount of the limiting substrate throwing out of the fermentor - ₁, ₂ dual variables of Lagrange's function - steps in steady state coordination procedure - errors values for steady state coordination process - _v , v=x, s conjugate variables of Lagrange's functional - _v , v=x,s penalty coefficients of augmented Lagrange's functional - _v , v=x, s interconnections of the time - e _v , v=x,s, D, _x , _s gradients of Lagrange's functional - j, l indexes of calculation procedures - values of errors in calculations The researches was supported by National Scientific Research Foundation under grants No NITN428/94 and No NITN440/94