Temperature control in solid substrate fermentation through discontinuous rotation

A laboratory-scale system for controlled dynamic solid substrate fermentation was developed and tested. The fermentation takes place in a stainless steel discontinuously rotating drum reactor, under controlled conditions of temperature, gas composition, relative humidity and direction and rate of rotation. The system was tested on a model fermentation of soya beans with Rhizopus oligosporus. In contrast to the traditional tempe fermentation, a granular product is obtained and build-up of heat and mass gradients is restricted. Despite the discontinuous rotation, the fungal growth continues, as evidenced by the production of heat. The rate of cooling depends on the temperature of the gas flushed through the reactor, the gas flow rate and the lenght of the rotation period. As a consequence of the homogeneous temperature control, the fungal heat development continued up to 70 h of fermentation. This is in clear contrast with the traditional tempe fermentation, which is already limited after 36 h by its own heat accumulation. Correspondence to: M. J. R. Nout     

Protein entrainment during baker's yeast fermentation on a semi-solid substrate in an air-fluidized bed fermentor

Baker's yeast was grown on a semi-solid substrate (homogenized whole potatoes) in an air-fluidized bed fermentor, in which a rapid stream of air simultaneously supplied oxygen and mixed the semi-solid substrate. The potato starch was converted to reducing sugars by -amylase (from Aspergillus).During the course of the batch fermentation, some secreted yeast proteins were trapped by sparging the effluent air into a water chamber. Surprisingly, neither the -amylase nor the potato proteins were the most predominant proteins carried over to the overhead collector during the 24 h run, even though they were the most abundant proteins in the fermentation mash. Fractionation of the yeast-produced proteins during this carry-over process is described, based on gel electrophoresis analyses of both the carried-over proteins and the extracellular proteins in the fermentation bed. Effects of the operating variables on the extracellular protein levels in the fermentation bed and the proteins in the overhead collector are also discussed.     

Validation of a model describing two-dimensional heat transfer during solid-state fermentation in packed bed bioreactors

A two-dimensional heat transfer model was validated against two experimental studies from the literature which describe the growth of Aspergillus niger during solid-state fermentation in packed bed bioreactors. With the same set of model parameters, the two-dimensional model was able to describe both radial temperature gradients, which dominated in one of the studies, and axial temperature gradients, which dominated in the other study. The sensitivity of the model predictions to the characteristics of the substrate and the microbe were explored. The temperatures reached in the column are most sensitive to parameters which affect the peak heat load, including the substrate packing density, the maximum specific growth rate, and the maximum biomass concentration. Even though the bed is assumed to be aerated with saturated air, the increase in temperature with bed height increases the water-carrying capacity of the air and therefore enables evaporation to contribute significantly to cooling. The model suggests that evaporation can remove as much as 78% of the heat from the bed during times of peak heat generation. Our model provides a tool which can guide the design and operation of packed bed bioreactors. However, further improvements are necessary to do this effectively, the most important of which is the incorporation of a water balance.     

Evaporative temperature and moisture control in solid substrate fermentation

Summary An integrated computerized control system, consisting of temperature and moisture sensors, a variable relative humidity air stream and water sprayers was used to control temperature and moisture in the solid substrate fermentation of extruded corn withRhizopus oligosporus in a 15 l rotary drum fermenter. Dry air was blown through the substrate to force evaporative cooling, balanced by spraying of cold water to maintain constant moisture.     

法夫酵母生产虾青素发酵条件的研究

方法：分别进行了接种时间、摇床转速、接种量和装液量对法夫酵母细胞生产虾青素摇瓶发酵过程影响的实验,比较了DMSO法、酸热法、碱法和自溶法等破壁方法和提取溶剂之间的差别,测定了法夫酵母生长过程中的生物量、类胡萝卜素产量和培养基中的残糖。结果：确定了最佳的摇瓶发酵条件为：种瓶至发酵摇瓶的接种时间为40h,摇床转速为160r/min,接种量为10%,装液量为50mL;DMSO法和丙酮分别为合适的破壁方法和提取溶剂。结论：初步确定发酵的基本条件,为进行法夫酵母高产虾青素菌种的筛选以及发酵培养基的优化奠定了基础。     

Water and water activity in the solid state fermentation of cassava starch by Aspergillus niger

Summary During the solid state fermentation (SSF) of cassava starch by Aspergillus niger estimations were made of total water, consumed water and the residual water remaining in small quantities after 23 h. A theoretical calculation based on the Ross equation showed that the water activity (a _w) of the substrate decreased to 0.85 towards the end of the culture. Such low values were assumed to be inhibitory to growth. The a _w of the substrate was increased when sugarcane bagasse was used as a high water retention capacity support. Higher growth rates and substrate conversion to biomass were obtained with this system, confirming that water availability is a critical factor in the SSF of starch substrates.Abbreviations A, B Experimental constants - a _w Water activity - H₂O_c Consumed water - H₂O_R Residual water - H₂O_T Total water - IDW Initial dry weight - IMC Initial moisture content - OUR Oxygen uptake rate - S Substrate dry weight - Sc Substrate conversion: consumed substrate/initial substrate - S _H Amount of sugars hydrolysed - SSF Solid state fermentation - X Biomass dry weight - W ^* Amount of solids/g of water     

Inhibition of alcoholic fermentation by substrate and ethanol

The effect of ethanol and sugars on rates of fermentation was studied. We used a strain of Canadida pseudotropicalis. The specific rate of fermentation was determined by using the Warburg manometer. The effect of ethanol was formulated as an exponential function of ethanol concentration, but the empirical constant was different when glucose or lactose was used as a substrate. The effects of both ethanol and substrate were formulated. It was demonstrate that when lactose and glucose were present in the medium with a small amount of alcohol, a synergistic effect on the rate of fermentation appeard. This phenomenon considerably limits the rate of fermentation.     

Kinetics of potato starch fermentation by Schwanniomyces castellii

The growth behaviour of Schwanniomyces castellii in slurry fermentation systems using untreated potato starch as substrate was studied in order to asses the eventual effect of the initial concentration of substrate (S_o) on cell growth rate. By applying the elementary balance method in combination with a Monod-type kinetic equation it was possible to formulate not only an unstructured model, but also the stoichiometry for such a yeast fermentation process. From a kinetic viewpoint, the Monod model was found to be redundant with respect to the pseudo-first order one, it being impossible to discriminate the contribution of v _M and K _S on the overall fermentation kinetics. Whereas the main yield coefficients appeared to be independent of S _O, the pseudo-first order rate constant was found to be inversely proportional to S _O. Therefore, cell growth appears to be controlled by the initial amount of amylolytic enzymes, that is to some extent proportional to the inoculum size, instead of the initial concentration of potato starch, at least within the experimental range of 3 to 30 g dm³.     

Mass balance and thermodynamic description of solid state fermentation of lignocellulosics byPleurotus ostreatus for animal feed production

This study was focused primarily on the degradation of lignin in water hyacinth and barley straw for animal-feed production. The experiment was performed in a 1.5-L Applikon fermenter for 30 days, varying the air flow rate from 0.022 VVM/0.047 VMM to 0.048 VVM/0.102 VMM. A novel approach was introduced for prediction of a kinetic model by using instantaneous respiratory quotient (RQ) measurements and steady state elemental balances. Growth kinetics were determined for the fungus in a 30-day fermentation with a mixture of barley straw and water hyacinth as the substrate. The instantaneous heat-interaction profile was predicted from steady state balances. Fermentation data were checked for consistency using the entropy balance inequality, and thermodynamic efficiency was calculated to show that degradation of lignocellulosics byPleurotus ostreatus followed more than one metabolic pathway during the course of the fermentation. Growth ofP. ostreatus on lignocellulosics, such as water hyacinth and barley straw, was di-auxic or possibly tri-auxic during the 30 days of fermentation.     

Enhancement and stabilization of the production of glucoamylase by immobilized cells of Aureobasidium pullulans in a fluidized-bed reactor

Summary Glucoamylase production by Aureobasidium pollulans A-124 was compared in free-living cells, cells immobilized in calcium alginate gel beads aerated on a rotary shaker (agitation rate 150 rpm), and immobilized cells aerated in an air bubble column reactor. Fermentation conditions in the bioreactor were established for bead concentration, substrate (starch) concentration, calcium chloride addition to the fermentation medium, and rate of aeration. Production of glucoamylase was optimized at approximately 1.5 units of enzyme activity/ml medium in the bioreactor under the following conditions: aeration rate, 2.0 vol air per working volume of the bioreactor (280 ml) per minute; gel bead concentration, 30% of the working volume; substrate (starch) concentration, at 0.3% (w/v); addition of calcium chloride to the medium at a final concentration of 0.01 M. Productivity levels were stabilized through the equivalent of ten batches of medium with the original inoculum of immobilized beads. Offprint requests to: M. Petruccioli     

西藏林芝地区农田土壤蒸发对大气温湿度的响应

蒸发是土-气界面上水分损失和水循环的重要组成因子,受到环境温湿度条件的强烈影响。为阐明高原背景条件下土壤蒸发速率对大气温湿度因子的响应,以西藏林芝农田裸地为研究对象,采用土壤H₂O/CO₂通量仪自动测定土壤表面水分蒸发速率、近地层气温、大气湿度等因子,并通过相关性分析研究变量间的相关关系。结果表明,土壤水分蒸发速率表现为单峰型日变化特征,最大值出现在午后14:00-15:00时,最小值出现在夜间,气温和大气湿度也表现相似的变化特征。土壤蒸发速率与气温之间呈极显著正相关关系(R>0.9, P<0.001),近地层大气湿度对土壤蒸发速率有极显著的正响应关系(R>0.7, P<0.001)。     

Operating characteristics of solid-state fermentation bioreactor with air pressure pulsation

The development of solid state fermentation (SSF) technology is very important to the production of cellulase and ultimately to the utilization of natural cellulose. However, inadequate dissipation of heat generated by biological activities has prevented solid-state fermentation from large-scale applications. The paper deals with the development of a novel SSF bioreactor with air pressure pulsation. By developing a measurement and control system under the Virtual Instrument (VI) concept, the performance of the SSF bioreactor with pressure pulsation was studied by cultivating Trichoderma koningii in solid medium made of wheat bran and corncob. The cooling effects of pressure pulsation on solid porous beds are discussed. Experimental results show that pressure pulsation enhances medium moisture evaporation, and hence, heat dissipation. Furthermore, through changing the pressure pulsation directions, it is able to mitigate the temperature gradients in the bioreactor. To sum up, pressure pulsation can provide the microbes with a growing environment at optimal temperature and medium water content. The text was submitted by the authors in English.     

Effect of operating conditions on solid substrate fermentation

In this work the effects of environmental parameters on the performance of solid substrate fermentation (SSF) for protein production are studied. These parameters are (i) air flow rate, (ii) inlet air relative humidity, (iii) inlet air temperature, and (iv) the heat transfer coefficient between the outer wall of the fermentor and the air in the incubator. The air flow is supplied to effect cooling of the fermented mass by evaporation of water. A dynamic model is developed, which permits estimation of biomass content, total dry matter, moisture content, and temperature of the fermented matter. The model includes the effects of temperature and moisture content on both the maximum specific growth rate and the maximum attainable biomass content. The results of the simulation are compared with actual experimental data and show good agreement with them. The most important conclusions are that (i) the evaporative cooling of the biomass is very effective for temperature control and (ii) the air flow rate and the heat transfer coefficient have strong effects but they affect the biomass morphology and are not controllable easily. Also, a simple technique for the determination of the optimum temperature and moisture content profile for cell protein production is applied. The simulated biomass production increases considerably employing the optimum temperature and moisture content profiles. The ultimate goal is to implement the determined effects of the environmental parameters on the SSF biomass production and the temperature and moisture variation profiles to effectively control the SSF and optimize the biomass production. (c) 1993 John Wiley & Sons, Inc.     

Effect of boundary layer conductance on the response of stomata to humidity

Abstract. Leaf conductance responses to leaf to air water vapour partial pressure difference (VPD) have been measured at air speeds of 0.5 and 3.0 ms⁻¹ in single attached leaves of three species in order to test the hypothesis that leaf conductance response to VPD is controlled by evaporation from the outer surface of the epidermis, rather than by evaporation through stomata. Total conductance decreased linearly with increassing VPD at both air speeds, but was decreased 1.6 3.0 times as much as by a given incrase in VPD at high than at low air speed. depending on species. In all species the relationship between leaf conductance and the gradient for evaporation from the epidermis was the same at both values of boundary layer conductance, supporting the hypothesis that direct epidermal evaporation controls stomatal guard cell behaviour in responses of stomata to VPD in these species.     

Optimization of the production of progesterone 11α-hydroxylase by Rhizopus nigricans

The progesterone 11α-hydroxylase of Rhizopus nigricans ATCC 6227b is an inducible enzyme system that is primarily induced by its substrate progesterone. Maximum induction was found at a progesterone concentration of 0.5 g/liter or above. Oxygen is the other substrate for the hydroxylation and this was found to have a major effect on the amounts of hydroxylase synthesized. Optimum induction of the hydroxylase in a fermentation with a 3.1 m/sec impeller tip speed was found to occur at a dissolved oxygen tension (DOT) of 10% of air saturation. The agitation rate also effects the amount of hydroxylase synthesized with an apparent maximum at 3.1 m/sec impeller tip speed. The DOT for a maximum hydroxylation rate was much higher than for enzyme synthesis so that it was preferable to increase the DOT after induction was completed.     

Ethanol vapour pressure as a control factor during alcoholic fermentation

Aqueous solutions of glucose/fructose mixtures with varying concentrations of ethanol were used to study the effects on fermentation of ethanol vapour pressure and water activity. Water vapour pressure was found to increase significantly with temperature in the range 15 to 30‡C. The effects on glucose fermentation bySaccharomyces cerevisiae Bg7FL of the variables glucose concentration, Tween 80 concentration, temperature and ammonium and ethanol concentrations were examined using central composite design. A best fit equation describing the main, quadratic and interactive effects of the five variables on yeast growth rate was produced. Further model systems were analysed in which the effects of ethanol vapour pressure, water vapour pressure and ethanol concentration on maximal growth rate of the yeast strain were studied. Above 18‡C, neither ethanol concentration nor ethanol vapour pressure controlled the fermentation rate. Ethanol toxicity was shown to be associated with its vapour pressure rather than its concentration.     

Mixed-feed exponential feeding for fed-batch culture of recombinant methylotrophic yeast

A simple, accurate model capable of predicting cell growth and methanol utilization during the mixed substrate fed-batch fermentation of Mut^S recombinant Pichia pastoris was developed and was used to design an exponential feeding strategy for mixed substrate fed-batch fermentation at a constant specific growth rate. Mixed substrate feeding has been shown to boost productivity in recombinant fed-batch culture of P. pastoris, while fixed growth rate exponential feeding during fed-batch culture is a useful tool in process optimization and control.     

Evaporation rate enhancement of water with air ions from a corona discharge

Space charges (air ions) produced by a single point-to-plane corona electrode system were used to study the enhancement in the evaporation rates of water at three ion current levels. The maximum evaporation rates of 0.019 and 0.017 g·min^?1 were observed at a 1 cm electrode gap for negative and positive air ions, respectively. The cumulative evaporation rates were linear with time and an ion-enhanced rate was about 4 times greater than the control. The current density distribution measurements agreed fairly well with those predicted from the Warburg law. The principal driving force for the observed evaporation enhancement was an ion drag phenomenon which created vortex motions in water when air ions were subjected to an externally applied electric field. Theoretical considerations from derived relationships in fluid mechanics demonstrate that the mass transfer coefficient is higher for positive than negative ions of the same current strength because of the mobility difference between the charges in the medium.     

Development of a stepwise aeration control strategy for efficient docosahexaenoic acid production by Schizochytrium sp.

The effect of aeration on the performance of docosahexaenoic acid (DHA) production by Schizochytrium sp. was investigated in a 1,500-L bioreactor using fed-batch fermentation. Six parameters, including specific growth rate, specific glucose consumption rate, specific lipid accumulation rate, cell yield coefficient, lipid yield coefficient, and DHA yield coefficient, were used to understand the relationship between aeration and the fermentation characteristics. Based on the information obtained from the parameters, a stepwise aeration control strategy was proposed. The aeration rate was controlled at 0.4 volume of air per volume of liquid per minute (vvm) for the first 24 h, then shifted to 0.6 vvm until 96 h, and then switched back to 0.4 vvm until the end of the fermentation. High cell density (71 g/L), high lipid content (35.75 g/L), and high DHA percentage (48.95%) were achieved by using this strategy, and DHA productivity reached 119 mg/L h, which was 11.21% over the best results obtained by constant aeration rate.     

Effect of controlled substrate feeding on butyric acid production byClostridium tyrobutyricum

Summary Production of butyric acid from wheat flour hydrolysate was studied withClostridium tyrobutyricum. The mode of substrate supply was found a key parameter for fermentation performance as large improvements were obtained by feeding with a non-limiting supply of substrate. With this procedure, increases in product concentration and productivity but also in selectivity and yield for butyrate were obtained. Substrate feeding controlled by the rate of gas production was found preferable to constant rate feeding for reason of convenience and flexibility. In these conditions, a butyrate concentration of 62.8 gl^–1 was obtained with a productivity of 1.25 gl^–1 h^–1, a selectivity of 91.5% and a yield of 0.45 g per g of glucose.