Johan Claes

Practical Identification of Unstructured Growth Kinetics by Application of Optimal Experimental Design

This paper deals with the practical identification of the parameters of unstructured growth kinetics during growth of biomass on one limiting substrate in a fed‐batch bioreactor. We consider kinetic models in which the specific growth rate is a function of the substrate concentration only. Two classes of models are distinguished: non‐monotonickinetics (with the Haldanemodel as a prototype) and monotonickinetics (with the Monodmodel as a prototype) . The information content of several simulation experiments, each with a different volumetric feed rate profile is evaluated by using the modified E‐criterion for optimal experimental design (i.e., ratio of the largest to the smallest eigenvalue of the Fisher information matrix) . The main contribution of this paper is to provide theoretical evidence and to present illustrative examples for the following conjecture: A feed rate strategy which is optimal in the sense of process performance, is an excellent starting point for feed rate optimization with respect to estimation of those parameters with large influence upon process performance. For a two degrees of freedom optimization of the feed rate profile, we obtain for the first time a modified E‐criterion value equal to 1, which is the optimal value for this criterion.

Model-based temperature control in ovens

The performance of an oven cavity is improved by implementing more advanced control algorithms to the unit. This improvement is necessary to cope with the more stringent requirements of the food market. It is shown with experimental results that the dynamic behavior of the oven cavity is modified significantly through the implementation of a model-based tuned P.I.D. controller. For this purpose, a mathematical model representing the main temperature dynamics of the oven cavity, is identified and validated. Afterwards, this mathematical model is used for tuning of the controller parameters, which allows a fast, safe and inexpensive off-line search for the optimal parameter set. In addition, the effect of practical constraints such as bounds and discretization effects can be examined quite easily. The model-based tuning approach for temperature control of an oven cavity is found to be successful. The application also illustrates the use of advanced measurement and control hardware and software.

Combining yield coefficients and exit-gas analysis for monitoring of the baker's yeast fed-batch fermentation

Abstract Bakers yeast is one of the micro-organisms that is studied most in literature. Therefore, a lot of knowledge on the biochemical pathways and corresponding yield coefficients is available. This knowledge is combined with measurements of oxygen and carbon dioxide in the exit-gas to determine the coefficients appearing in the stoichiometric equations. In this manner, two measurements are sufficient to yield on-line estimates for biomass, glucose, ethanol and the specific growth rate, and information about the (ill-defined) nitrogen source NHq. This is not possible if the yield coefficients are not included in the estimation procedure. A sensitivity analysis illustrates that this estimation scheme is rather insensitive to uncertainties on the yield coefficients.

HEURISTIC FEED RATE PROFILES FOR OPTIMAL YIELD AND PRODUCTIVITY OF FED-BATCH BIOPROCESSES

Abstract The optimization of two important classes of fed-batch fermentation processes with respect to the limiting substrate feed rate is considered: (i) growth of one biomass on one limiting substrate, and (ii) growth and product formation on one substrate. For these two types of bioprocesses, two different performance criteria are compared: yield and productivity. Heuristic Teed rate profiles are derived based on (i) the optimal control solution according to the minimum principle, and (ii) the qualitative behavior of the specific rates for growth and possibly product formation. For biomass production processes, it is illustrated that the heuristic strategy coincides exactly with the optimal control solution, while its structure is independent of the performance index considered. For product formation processes, it is illustrated that the same heuristic approach can be used to optimize both yield and productivity in spite of the well known conflict between them.

On-line monitoring and optimal adaptive control of the fed-batch baker's yeast fermentation

Abstract In this paper an experimental validation of on-line monitoring and optimal adaptive control strategies for the baker’s yeast fermentation is presented. The online monitoring strategy consists of an on-line biomass measurement (based on a capacitance measure), which is exploited to estimate the specific growth rate by using an observer based estimator. The model based control algorithm is an adaptive linearizing control law, which keeps the estimated specific growth rate constant during the fermentation. Special attention is devoted to the tuning of the estimator and the controller.

Microbial Dynamics during Industrial Rearing, Processing, and Storage of Tropical House Crickets (Gryllodes sigillatus) for Human Consumption

ABSTRACT In this study, the microbiota during industrial rearing, processing, and storage of the edible tropical house cricket, Gryllodes sigillatus, was investigated. To this end, we analyzed samples from the cricket feed, obtained before feeding as well as from the cages, and from the crickets during rearing, after harvest, and after processing into frozen, oven-dried, and smoked and oven-dried (smoked/dried) end products. Although the feed contained lower microbial numbers than the crickets, both were dominated by the same species-level operational taxonomic units, as determined by Illumina MiSeq sequencing. They corresponded, among others, to members of Porphyromonadaceae, Fusobacterium, Parabacteroides, and Erwinia. The harvested crickets contained high microbial numbers, but none of the investigated food pathogens Salmonella spp., Listeria monocytogenes, Bacillus cereus, or coagulase-positive staphylococci. However, some possible mycotoxin-producing fungi were isolated from the crickets. A postharvest heat treatment, shortly boiling the crickets, reduced microbial numbers, but an endospore load of 2.4 log CFU/g remained. After processing, an increase in microbial counts was observed for the dried and smoked/dried crickets. Additionally, in the smoked/dried crickets, a high abundance of a Bacillus sp. was observed. Considering the possible occurrence of food-pathogenic species from this genus, it is advised to apply a heat treatment which is sufficient to eliminate spores. Nevertheless, the microbial numbers remained constant over a 6-month storage period, whether frozen (frozen end product) or at ambient temperature (oven-dried and smoked/dried end products). IMPORTANCE The need for sustainable protein sources has led to the emergence of a new food sector, producing and processing edible insects into foods. However, insight into the microbial quality of this new food and into the microbial dynamics during rearing, processing, and storage of edible insects is still limited. Samples monitored for their microbiota were obtained in this study from an industrial rearing and processing cycle. The results lead first to the identification of process steps which are critical for microbial food safety. Second, they can be used in the construction of a Hazard Analysis and Critical Control Points (HACCP) plan and of a Novel Food dossier, which is required in Europe for edible insects. Finally, they confirm the shelf-life period which was determined by the rearer.

Modelling and dynamical analysis of unitank biological wastewater

By applying modern model based control theory to biotechnological systems such as wastewater treatment plants important process improvements can be expected. Mathematical (low complexity) models, useful for dynamical optimization of systems and for the design of on-line model based controllers have been developed. A new technique, based on equilibrium lines in the state space domain, is introduced to analyze the dynamic behavior of such systems. The use of sensitivity studies as a tool to discriminate between different model structures is clearly illustrated

Heuristic Feed Rate Profiles for Optimal Yield and Productivity of Fed-Batch Bioprocesses

Abstract The optimization of two important classes of fed-batch fermentation processes with respect to the limiting substrate feed rate is considered: (i) growth of one biomass, and (ii) growth and product formation. Two different performance criteria are compared: yield and productivity. Heuristic feed rate profiles are derived based on (i) the optimal control solution according to the minimum principle, and (ii) the qualitative behavior of the specific rates for growth and possibly product formation. For biomass production processes, the heuristic strategy coincides exactly with the optimal control solution and is independent of the performance index considered. For product formation processes, the same heuristic approach can be used to optimize both yield and productivity in spite of the well known conflict between them.

Microbial characterisation of the edible grasshopper Ruspolia differens in raw condition after wild-harvesting in Uganda

This research aimed at establishing the chemical intrinsic properties and the microbial quality of an edible grasshopper Ruspolia differens and the effect of its source (geographical area) in Uganda, trading point, swarming season and plucking on these parameters. The intrinsic properties of the grasshopper can support the growth of a wide variety of microorganisms. High counts of total aerobic microbes, Enterobacteriaceae, lactic acid bacteria, total aerobic spores, and yeasts and moulds were obtained. Metagenetic analyses yielded 1793 Operational Taxonomic Units (OTUs) belonging to 24 phyla. Actinobacteria, Bacteroidetes, Firmicutes, Fusobacteria and Proteobacteria were the most abundant phyla, while members of the genera Acinetobacter, Buttiauxella, Lactococcus, Staphylococcus and Undibacterium were the most abundant OTUs. A number of genera harbouring potential pathogens (Acinetobacter, Bacillus, Buttiauxella, Campylobacter, Clostridium, Staphylococcus, Pseudomonas and Neisseria) were identified. The geographical area, trading point, swarming season and plucking significantly influenced microbial counts and bacterial diversity. The high microbial counts predispose R. differens to fast microbial spoilage, while the presence of Clostridium and Campylobacter makes this grasshopper a potential source of food borne diseases. Further research should identify the specific spoilage microorganisms of R. differens and assess the characteristics of this grasshopper that support growth of food pathogens.

Sensitivity Analysis of a Linearizing Controller for the Fed-Batch Baker's Yeast Fermentation

Abstract Feedback linearizing control of the fed-batch bakers yeast fermentation process is studied. Special attention is devoted to the tuning of the linearizing controller with respect to errors in the yield YX/S and the influent substrate concentration CS,in. If the controller timing does not incorporate possible errors in YX/S and CS/in, the performance of the controller, defined as the deviation from the setpoint of the specific growth rate, decreases considerably. This is illustrated by experimental data and by simulations. A sensitivity analysis with respect to errors in YX/S and CS,in, indicates that better performance can be obtained if the uncertainty on these parameters is taken into account. This is also validated with an experiment and by simulation.