Identifying Variables Influencing Traditional Food Solid-State Fermentation by Statistical Modeling.

Solid-state fermentation is widely used in traditional food production, but most of the complex processes involved were designed and are carried out without a scientific basis. Often, mathematical models can be established to describe mass and heat transfer with the assistance of chemical engineering tools. However, due to the complex nature of solid-state fermentation, mathematical models alone cannot explain the many dynamic changes that occur during these processes.

Water dynamics during solid-state fermentation by Aspergillus oryzae YH6.

Water is crucial for microbial growth, heat transfer and substrate hydrolysis, and dynamically changes with time in solid-state fermentation. However, water dynamics in the solid substrate is difficult to define and measure. Here, nuclear magnetic resonance was used to monitor water dynamics during the pure culture of Aspergillus oryzae YH6 on wheat in a model system to mimic solid starter (Qu or Koji) preparation.

Optimizing carbon dioxide utilization for microalgae biofilm cultivation.

The loss of carbon dioxide (CO ) to the environment during microalgae cultivation is undesirable for both environmental and economic reasons. In this study, a phototrophic biofilm growth model was developed and validated with the objective to maximize both CO utilization efficiency and production of microalgae in biofilms. The model was validated in growth experiments with CO as the limiting substrate.

Deceleration-stats save much time during phototrophic culture optimization.

In case of phototrophic cultures, photobioreactor costs contribute significantly to the total operating costs. Therefore one of the most important parameters to be determined is the maximum biomass production rate, if biomass or a biomass associated product is the desired product. This is traditionally determined in time consuming series of chemostat cultivations.

A model for customising biomass composition in continuous microalgae production.

A kinetic model is presented that describes functional biomass, starch and storage lipid (TAG) synthesis in the microalga Neochloris oleoabundans as a function of nitrogen and light supply rates to a nitrogen-limited turbidostat cultivation system. The model is based on the measured electron distribution in N. oleoabundans, which showed that starch is the primary storage component, whereas TAG was only produced after an excess of electrons was generated, when growth was limited by nitrogen supply.

Modeling microalgal flocculation and sedimentation.

In this study, a combined flocculation and sedimentation model is developed. The model predicts the time needed to reach a desired concentration of microalgal suspension in a sedimentation tank. The concentration of the particles as function of the time and the position in the tank is described.

Modeling growth, lipid accumulation and lipid turnover in submerged batch cultures of Umbelopsis isabellina.

The production of lipids by oleaginous yeast and fungi becomes more important because these lipids can be used for biodiesel production. To understand the process of lipid production better, we developed a model for growth, lipid production and lipid turnover in submerged batch fermentation. This model describes three subsequent phases: exponential growth when both a C-source and an N-source are available, carbohydrate and lipid production when the N-source is exhausted and turnover of accumulated lipids when the C-source is exhausted.

Modeling lipid accumulation in oleaginous fungi in chemostat cultures: I. Development and validation of a chemostat model for Umbelopsis isabellina.

Lipid-accumulating fungi may be able to produce biodiesel precursors from agricultural wastes. As a first step in understanding and evaluating their potential, a mathematical model was developed to describe growth, lipid accumulation and substrate consumption of the oleaginous fungus Umbelopsis isabellina (also known as Mortierella isabellina) in submerged chemostat cultures. Key points of the model are: (1) if the C-source supply rate is limited, maintenance has a higher priority than growth, which has a higher priority than lipid production; (2) the maximum specific lipid production rate of the fungus is independent of the actual specific growth rate.

Modeling lipid accumulation in oleaginous fungi in chemostat cultures. II: Validation of the chemostat model using yeast culture data from literature.

A model that predicts cell growth, lipid accumulation and substrate consumption of oleaginous fungi in chemostat cultures (Meeuwse et al. in Bioproc Biosyst Eng. doi: 10.

Microbiology of synthesis gas fermentation for biofuel production.

A significant portion of biomass sources like straw and wood is poorly degradable and cannot be converted to biofuels by microorganisms. The gasification of this waste material to produce synthesis gas (or syngas) could offer a solution to this problem, as microorganisms that convert CO and H2) (the essential components of syngas) to multicarbon compounds are available. These are predominantly mesophilic microorganisms that produce short-chain fatty acids and alcohols from CO and H2.

Modeling conversion and transport phenomena in solid-state fermentation: a review and perspectives.

Solid-state fermentation (SSF) is accompanied inevitably by development of concentration and temperature gradients within the substrate particles and microbial biofilms. These gradients are needed for driving the transport of substrates and products. In addition, concentration gradients have been suggested to be crucial for obtaining the characteristics that define the products of SSF; nevertheless, gradients are also known to result in reduced productivity and unwanted side reactions.

Significance of bed porosity, bran and specific surface area in solid-state cultivation of Aspergillus oryzae.

In this paper, the effects of bed porosity, bran and specific surface area on the oxygen uptake rate and alpha-amylase production during growth of Aspergillus oryzae on wheat grain and wheat-flour substrate are reported. The high oxygen uptake rate found during cultivation of A. oryzae on wheat-flour substrate was not reached on wheat grain.

Effect of low oxygen concentrations on growth and alpha-amylase production of Aspergillus oryzae in model solid-state fermentation systems.

Oxygen transfer in the fungal mat is a major concern in solid-state fermentation (SSF). Oxygen supply into the mycelial layers is hampered by diffusion limitation. For aerobic fungi, like Aspergillus oryzae, this oxygen depletion can be a severely limiting factor for growth and metabolite production.

Limitations of membrane cultures as a model solid-state fermentation system.

Aims: To examine the reliability of membrane cultures as a model solid-state fermentation (SSF) system.

Methods And Results: In overcultures of Aspergillus oryzae on sterilized wheat flour discs overlaid with a polycarbonate membrane, we demonstrated that the presence of membrane filters reduced the maximum respiration rate (up to 50%), and biomass and alpha-amylase production. We also show that the advantage of membrane cultures, i.

Combined discrete particle and continuum model predicting solid-state fermentation in a drum fermentor.

The development of mathematical models facilitates industrial (large-scale) application of solid-state fermentation (SSF). In this study, a two-phase model of a drum fermentor is developed that consists of a discrete particle model (solid phase) and a continuum model (gas phase). The continuum model describes the distribution of air in the bed injected via an aeration pipe.

Polyol accumulation by Aspergillus oryzae at low water activity in solid-state fermentation.

Polyol accumulation and metabolism were examined in Aspergillus oryzae cultured on whole wheat grains or on wheat dough as a model for solid-state culture. In solid-state fermentation (SSF), water activity (a(w)) is typically low resulting in osmotic stress. In addition to a high level of mannitol, which is always present in the cells, A.

Numerical simulation and PEPT measurements of a 3D conical helical-blade mixer: a high potential solids mixer for solid-state fermentation.

Helical-blade solids mixers have a large potential as bioreactors for solid-state fermentation (SSF). Fundamental knowledge of the flow and mixing behavior is required for robust operation of these mixers. In this study predictions of a discrete particle model were compared to experiments with colored wheat grain particles and positron emission particle tracking (PEPT) measurements.

Substrate aggregation due to aerial hyphae during discontinuously mixed solid-state fermentation with Aspergillus oryzae: experiments and modeling.

Solid-state fermentation (SSF) is prone to process failure due to channeling caused by evaporative cooling and the formation of an interparticle mycelium network. Mixing is needed to break the mycelium network and to avoid such failure. This study presents the first attempt to quantify and predict the effect of mycelium bonds on particle mixing and vice versa.

Aspergillus oryzae in solid-state and submerged fermentations. Progress report on a multi-disciplinary project.

We report the progress of a multi-disciplinary research project on solid-state fermentation (SSF) of the filamentous fungus Aspergillus oryzae. The molecular and physiological aspects of the fungus in submerged fermentation (SmF) and SSF are compared and we observe a number of differences correlated with the different growth conditions. First, the aerial hyphae which occur only in SSFs are mainly responsible for oxygen uptake.

Heat and water transfer in a rotating drum containing solid substrate particles.

In previous work we reported on the simulation of mixing behavior of a slowly rotating drum for solid-state fermentation (SSF) using a discrete particle model. In this investigation the discrete particle model is extended with heat and moisture transfer. Heat transfer is implemented in the model via interparticle contacts and the interparticle heat transfer coefficient is determined experimentally.

Water and glucose gradients in the substrate measured with NMR imaging during solid-state fermentation with Aspergillus oryzae.

Gradients inside substrate particles cannot be prevented in solid-state fermentation. These gradients can have a strong effect on the physiology of the microorganisms but have hitherto received little attention in experimental studies. We report gradients in moisture and glucose content during cultivation of Aspergillus oryzae on membrane-covered wheat-dough slices that were calculated from (1)H-NMR images.

Three-dimensional simulation of grain mixing in three different rotating drum designs for solid-state fermentation.

A previously published two-dimensional discrete particle simulation model for radial mixing behavior of various slowly rotating drums for solid-state fermentation (SSF) has been extended to a three-dimensional model that also predicts axial mixing. Radial and axial mixing characteristics were predicted for three different drum designs: (1) without baffles; (2) with straight baffles; and (3) with curved baffles. The axial mixing behavior was studied experimentally with video- and image-analysis techniques.

Contribution of aerial hyphae of Aspergillus oryzae to respiration in a model solid-state fermentation system.

Oxygen transfer is for two reasons a major concern in scale-up and process control in industrial application of aerobic fungal solid-state fermentation (SSF): 1) heat production is proportional to oxygen uptake and it is well known that heat removal is one of the main problems in scaled-up fermenters, and 2) oxygen supply to the mycelium on the surface of or inside the substrate particles may be hampered by diffusion limitation. This article gives the first experimental evidence that aerial hyphae are important for fungal respiration in SSF. In cultures of A.

Validation of a model for process development and scale-up of packed-bed solid-state bioreactors.

We have validated our previously described model for scale-up of packed-bed solid-state fermenters (Weber et al., 1999) with experiments in an adiabatic 15-dm(3) packed-bed reactor, using the fungi Coniothyrium minitans and Aspergillus oryzae. Effects of temperature on respiration, growth, and sporulation of the biocontrol fungus C.

Discrete particle simulations predicting mixing behavior of solid substrate particles in a rotating drum fermenter.

A soft-sphere discrete particle model was used to simulate mixing behavior of solid substrate particles in a slow rotating drum for solid-state fermentation. In this approach, forces acting on and subsequent motion of individual particles can be predicted. The (2D) simulations were qualitatively and quantitatively validated by mixing experiments using video and image analysis techniques.