Optimization of batch fermentation processes. I. Development of mathematical models for batch penicillin fermentations

Two kinds of mathematical models have been developed for batch penicillin fermentations: (1) general models, based on averaged, nondimensionalized cell and penicillin synthesis curves from plant, scale fermentors and (2) particular models developed from specific sets of experimental data from two sources. Parameter-temperature functions used with the general models were assumed to have general shapes which could apply to many fermentations, i.e., they were based on the familiar temperature response of enzyme-catalyzed reactions. Parameter-temperature functions for the particular models were determined from experimental data for batch runs at various temperatures.     

Optimization of batch fermentation processes by graphical method

A graphical method is proposed for batch fermentation process optimization. Its objective function is the maximum output of the product when the time of process is fixed or free. The technique of optimization is based on Bellman's dynamic programming concepts and the assumption that the process can be described by mathematical models of generalized structure. An example of the proposed technique's application is presented.     

Oscillatory penicillin formation in carbon-limited batch fermentations of Penicillium chrysogenum

Circadian oscillations of penicillin productivity with a period of 22±2 h have been observed in carbon-limited batch fermentations of Penicillium chrysogenum. The specific penicillin production rate oscillated with an amplitude of 20 to 100% of its mean value, depending on the growth rate of the active (respiring and producting) biomass. In spite of this, the penicillin concentration increased almost linearly if the optimum growth rate of the active biomass for maximum penicillin productivity was maintained using microprocessor control. This apparently inconsistent behaviour of the fungus is discussed on the basis of chaos theory.     

Optimal temperature control for batch beer fermentation

Optimal control theory was applied to the process of batch beer fermentation. The performance functional considered was a weighted sum of maximum ethanol production and minimum time. Calculations were based on the model of Engasser et al. modified to include temperature effects. Model parameters were determined from isothermal batch fermentations. The fermentor cooling duty was the single available control. Temperature state variable constraints as well as control variable constraints were considered. The optimal control law is shown to be bang-bang control with the existence of a singular arc corresponding to isothermal operation at the maximum temperature constraint. An iterative algorithm is presented for computing appropriate switching times using a penalty-function-augmented performance functional.     

Optimization of batch fermentation conditions for dextran production

The nutrient medium (containing sucrose, yeast extract and K₂HPO₄), temperature and initial pH conditions were optimised for batch dextran production in shake flask fermentations using a strain of Leuconostoc mesenteroides NRRL B 512 (F). A 2⁵⁻¹ fractional factorial central composite experimental design was attempted. Multistage Monte Carlo optimization program was used to maximize the multiple regression equation obtained. The optimal values of tested variables for maximal dextran production were found to be: sucrose, 300 g/l; yeast extract, 10 g/l; K₂HPO₄, 30 g/l; temperature, 23°C and initial pH 8.3 with a predicted dextran yield of 154 g/l.     

A new method for studying microaerobic fermentations. II. An experimental investigation of xylose fermentation

A new experimental technique, called oxygen programmed fermentation (OPF), was used to study microbial cultures of the years Pichia stipitis and Candida utilis growing on xylose as carbon and energy source. In the oxygen programmed fermentation, the inlet oxygen mole fraction was continuously changed to scan through a wide range of oxygen uptake rates in a continuous culture. The largest ethanol yields and productivities of P. stipitis were found at oxygen transfer rates below 1.5 mmol L(-1) h(-1). It was found that the ratio between the culture fluorescence and near-IR absorbance increased at oxygen transfer rates lower than 1.5 mmol L(-1) h(-1). Small amounts of ethanol were produced also by C. utilis when the oxygen transfer rate was between 0 and 3 mmol L(-1) h(-1). It is suggested that OPF will form a nice complement to ordinary, microaerobic chemostat experiments, by making the identification of interesting regions of oxygen transfer rates possible in an efficient and time-saving initial experiment. (c) 1994 John Wiley & Sons, Inc.     

An HPLC procedure for monitoring penicillin G fermentations

Summary An HPLC procedure for the quantification of the precursor, intermediates, product, and degradation product of penicillin G fermentations is described. The method involves the use of an acetonitrile gradient and direct UV detection with a total run-time of 45 minutes including column regeneration. The technique can be exploited for on-line monitoring of penicillin G fermentations using defined or complex media.     

Energy-based dynamic model for variable temperature batch fermentation by Lactococcus lactis

We developed a mechanistic mathematical model for predicting the progression of batch fermentation of cucumber juice by Lactococcus lactis under variable environmental conditions. In order to overcome the deficiencies of presently available models, we use a dynamic energy budget approach to model the dependence of growth on present as well as past environmental conditions. When parameter estimates from independent experimental data are used, our model is able to predict the outcomes of three different temperature shift scenarios. Sensitivity analyses elucidate how temperature affects the metabolism and growth of cells through all four stages of fermentation and reveal that there is a qualitative reversal in the factors limiting growth between low and high temperatures. Our model has an applied use as a predictive tool in batch culture growth. It has the added advantage of being able to suggest plausible and testable mechanistic assumptions about the interplay between cellular energetics and the modes of inhibition by temperature and end product accumulation.     

Optimization of batch alcoholic fermentation of glucose syrup substrate

The quantitative effects of substrate concentration, yeast concentration, and nutrient supplementation on ethanol content, fermentation time, and ethanol productivity were investigated in a Box–Wilson central composite design experiment, consisting of five levels of each variable, High substrate concentration, up to 30° Brix, resulted in higher ethanol content (i.e., up to 15.7% w/v or 19.6% v/v) but longer fermentation time and hence lower ethanol productivity. Increasing yeast concentration, on the other hand, resulted in shorter fermentation time and higher productivity. The highest ethanol productivity of about 21 g EiOH/L h was obtained at low substrate concentration (i.e., 12° Brix), low alcohol content (i.e., 6% by weight), high yeast concentration (i.e., 4.4%), and high supplementation of yeast extract (i.e., 2.8). Productivity of this magnitude is substantially higher that that of the traditional batch fermentation of fed-batch fermentation. It is comparable to the results of continuous fermentation but lower than those of vacuum fermentation but lower than those of vacuum fermentation. Optimal conditions for maximal ethanol productivity can be established by a multiple regression analysis technique and by plotting the contours of constant response to conform to the constraints of individual operations.     

Optimization of high molecular weight pullulan production by Aureobasidium pullulans in batch fermentations

Of five strains of Aureobasidium pullulans studied, NRRL Y-2311-1 yielded the highest titer (26.2 g/L) of pullulan and formed the lowest amount of melanin-like pigment. Sucrose was superior to glucose as the carbon and energy source on the basis of yield and titer of pullulan produced. Pullulan titer was higher (26.2 vs 5.1 g/L), biomass concentration was lower (6.9 vs 12.7 g/L), and DO was lower (0 vs 60% of saturation) when the fermenter was agitated by a marine propeller compared to Rushton impellers. Pullulan produced by strain NRRL Y-2311-1 ranged in weight-average molar mass (M(w)) from 486 KDa and number-average molar mass (M(n)) from 220 Da on day 1 of growth to 390 KDa and 690 Da on day 6; M(w) declined by about 35% from day 1 to day 3, the day of maximum pullulan titer. For the other strains, the ranges of molar mass on the day of maximum pullulan titer were 338-614 KDa (M(w)) and 100-6820 Da (M(n)).     

Optimization of cellulase production in batch fermentation byTrichoderma reesei

Maximum cellulase production was sought by comparing the activities of the cellulases produced by differentTrichoderma reesei strains andAspergillus niger. Trichoderma reesei Rut-C30 showed higher cellulase activity than otherTrichoderma reesei strains andAspergillus niger that was isolated from soil. By optimizing the cultivation condition during shake flask culture, higher cellulase production could be achieved. The FP (filter paper) activity of 3.7 U/ml and CMCase (Carboxymethylcellulase) activity of 60 U/ml were obtained from shake flask culture. When it was grown in 2.5L fermentor, where pH and DO levels are controlled, the Enzyme activities were 133.35 U/ml (CMCase) and 11.67 U./ml (FP), respectively. Ammonium sulfate precipitation method was used to recover enzymes from fermentation broth. The dried cellulase powder showed 3074.9 U/g of CMCase activity and 166.7 U/g of FP activity with 83.5% CMCase recovery.     

重组毕赤酵母产青霉素G酰化酶的分批发酵动力学研究

构建了重组毕赤酵母产青霉素G酰化酶的分批发酵动力学模型。实验考察了分批发酵过程中甘油消耗、甲醇浓度、菌体浓度、溶氧、补料时间对青霉素G酰化酶活力的影响。应用Matlab软件,对菌体生长、基质消耗和产物生成方程进行最优参数估算和非线性拟合,得到相应的动力学模型。模型的计算值与实验值能较好地拟合,表明所建模型能较好反映重组毕赤酵母产青霉素G酰化酶的分批发酵过程。     

Real time phase detection based online monitoring of batch fermentation processes

Industrial fermentations conducted in a batch or semi-batch mode demonstrate significant batch-to-batch variability. Current batch process monitoring strategies involve manual interpretation of highly informative but low frequency offline measurements such as concentrations of products, biomass and substrates. Fermentors are also fitted with computer interfaced instrumentation, enabling high frequency online measurements of several variables and automated techniques which can utilize this data would be desirable. Evolution of a batch fermentation, which typically uses complex medium, can be conceptualized as a sequence of several distinct metabolic phases. Monitoring of batch processes can then be achieved by detecting the phase change events, also termed as singular points (SP). In this work, we propose a novel moving window based real-time monitoring strategy for SP detection based only on online measurements. The key hypothesis of the strategy is that the statistical properties of the online data undergo a significant change around an SP. The strategy is easily implementable and does not require past data or prior knowledge of the number or time of occurrence of SPs. The efficacy of the proposed approach has been demonstrated to be superior compared to that of reported techniques for industrially relevant model organisms. The proposed approach can be used to decide offline sampling timings in real time.     

General characteristics of optimal feed rate profiles for various fed-batch fermentation processes

General Characteristics of the optimal feed rate profiles have been deduced for various fed-batch fermentation processes by analyzing singular controls and singular arcs. The optimal control sequences depend on the shapes of the specific growth and product formation rates, mu andpi, and the initial conditions. For fed-batch processes described by four mass balance equations, the most general optimal control sequence consists of a period of maximum feed rate, a period of minimum feed rate (a batch period), a period of singular feed rate (variable and intermediate), and a batch period. Degenerate sequences in which one or more periods are missing can result with a particular set of initial conditions. If the fermentation time is not critical, the singular control maximizes the net yield of product and only when the time is also important, it balances a trade off between the yield of product and the specific growth rate which dictates the fermentation time. With the sequence of optimal control known, the optimal feed rate profile determination is reduced to a problem of determining switching times.     

Optimum pH and temperature conditions for xylose fermentation by Pichia stipitis

Pichia stipitis NRRL Y-7124 is a xylose-fermenting yeast able to accumulate ca. 57 g/L ethanol. Because optimum process conditions are important, data were collected to determine the effects of temperature and pH on growth and fermentation rates and product accumulations. Temperatures (26-35 degrees C) providing optimum biomass and ethanol productivities did not necessarily provide maximum ethanol accumulation. Xylitol and residual xylose concentrations increased with temperature. Maximum ethanol selectivity was achieved at 25-26 degrees C with minimal sacrifice to production rates. The temperature optimum for xylose could not be generalized to glucose fermentations, in which ethanol productivity and accumulation were optimum at 34 degrees C. The optimum pH range for growth and fermentation on xylose was 4-7 at 25 degrees C.