Silviya Popova

Modeling of Batch Alcohol Fermentation with Free and Immobilized Yeasts Saccharomyces Cerevisiae 46 EVD

ABSTRACT Seven of the mathematical structures known by far were applied for modeling of batch alcoholic fermentation with free and immobilized cells of Saccharomyces cerevisiae strain 46 EVD using experimental data. The obtained models were analyzed and compared with respect to their quality and applicability for process simulation. Conclusions about the influence of cell immobilization on the batch process intensification were drawn based on analysis of the obtained model parameters. It was found that Monod-type model and logistic equation in combination with Ludeking-Piert model are the most appropriate structures for description of both free- and immobilized-cell fermentations for the investigated yeast strain.

Gap Filling of Daily Sea Levels by Artificial Neural Networks

In the recent years, intelligent methods as artificial neural networks are successfully applied for data analysis from different fields of the geosciences. One of the encountered practical problems is the availability of gaps in the time series that prevent their comprehensive usage for the scientific and practical purposes. The article briefly describes two types of the artificial neural network (ANN) architectures ‐ Feed‐ Forward Backpropagation (FFBP) and recurrent Echo state network (ESN). In some cases, the ANN can be used as an alternative on the traditional methods, to fill in missing values in the time series. We have been conducted several experiments to fill the missing values of daily sea levels spanning a 5‐years period using both ANN architectures. A multiple linear regression for the same purpose has been also applied. The sea level data are derived from the records of the tide gauge Burgas, which is located on the western Black Sea coast. The achieved results have shown that the performance of ANN models is better than that of the classical one and they are very promising for the real‐time interpolation of missing data in the time series. http://www.transnav.eu the International Journal on Marine Navigation and Safety of Sea Transportation Volume 7

Modeling Of Alcohol Fermentation In Brewing - Comparative Assessment Of Flavor Profile Of Beers Produced With Free And Immobilized Cells.

A detailed investigation of bioengineering constants for the accumulation of major yeast metabolites in beer produced by free and immobilized cells was carried out. The kinetic constants were used to determine the effect of immobilization on yeast metabolism. The esters synthesis dynamics was similar for the free and the immobilized cell which was confirmed by the kinetic model. The dynamics of the higher alcohol synthesis was comparable for the free and immobilized cell, but there were some differences. The dynamics of the higher alcohols accumulation for the free and immobilized cells was similar, but there were some differences between the two used strains. These differences were due to the influence of mass transfer between the liquid and the capsules, which reflected mostly in the metabolism of some amino acids. There were significant differences in the aldehyde synthesis and reduction by immobilized and free cells. The free cells of both yeast strains showed distinct maximum of aldehydes, where after the aldehydes reduction started. On the other hand, the aldehyde peaks were not so distinct for the immobilized cells and the aldehydes concentration was relatively constant during fermentation. The explanation for this difference can be found in the kinetic parameters. The model described with high accuracy the beer fermentations with immobilized and free cells and confirmed the experimental data. The obtained data would be used for developing of control strategy fermentation process to obtain beverages with different organoleptic profile. INTRODUCTION The main stages in the brewing process are: wort production; alcoholic fermentation and maturation; processing and stabilization of the beer (Kunze 2003; Handbook of brewing: Processes, Technology, Markets 2009). The wort transforms into beer during alcoholic fermentation and maturation. The ethanol fermentation occurs as a result of enzymatic activity of the yeast at Embden-Meyerhof Parnas pathway, which leads to glucose conversion to pyruvate. Under anaerobic conditions the yeasts convert pyruvate to ethanol and CO2. In aerobic conditions, yeasts consume sugars, mainly for biomass accumulation and CO2 production (Boulton and Quain, 2001). Yeast metabolism during fermentation and maturation affects significantly on beer flavor. Ethanol, CO2, esters and fusel alcohols have positive contributions to beer flavor. Dimethyl sulphide and hydrogen sulphide, diacetyl, and aldehydes contribute to flavor defects of beer (Meilgaard, 1975). Therefore, the synthesis and reduction of yeast metabolites on the microbiological and bioengineering levels have to be studied for the purpose of yeast by-products optimization in certain limits. Fermentation and maturation are the longest processes in brewing. The primary fermentation lasts between 3-6 days and the maturation up to 2 weeks depending on the fermentation type and the used equipment. In such a competitive market, the potential time savings, proposed by immobilized cell technology (ICT) have to be taken into account. Immobilized yeast cell technology allows the production of beer to be accomplished in as little as 2-3 days (Branyik et al, 2005). Immobilized cell systems are heterogeneous systems in which considerable mass transfer limitations can occur, resulting in a changed yeast metabolism (Willaert, 2007). Consequently, the main challenge for ICT is to reproduce the traditional beer flavor. Proceedings 27th European Conference on Modelling and Simulation ©ECMS Webjorn Rekdalsbakken, Robin T. Bye, Houxiang Zhang (Editors) ISBN: 978-0-9564944-6-7 / ISBN: 978-0-9564944-7-4 (CD) The aim of this work is to determine the influence of immobilization on the yeast metabolism using mathematical models. The dynamics of the main yeast metabolites ethanol and CO2, the biomass concentration and some of secondary yeast metabolites esters, aldehydes and higher alcohols were studied. The differences between fermentations with immobilized and free cells were determined by the developed mathematical models for yeast metabolites. MICROORGANISMS AND FERMENTATION CONDITIONS The fermentations were carried out with top-fermenting yeast strain Saccharomyces cerevisiae S-33 and bottomfermenting yeast strain Saccharomyces pastorianus S23. Wort with 3 different original extracts – 9, 11 and 13% was used for fermentations. All media were sterilized at 121 °С for 20 min before fermentations. Immobilization procedure and fermentation conditions were previously reported in (Parcunev et.al. 2012). In this study the fermentations with free and immobilized cells were investigated for the same intervals of time (10 days) to determine the impact of immobilization on the yeast metabolism. Although the fermentation with immobilized cells was faster than the one with free cells, the metabolites accumulation in the fermenting medium was influenced by diffusion limitations. Biomass concentration of immobilized cells was determined according to mathematical model proposed in (Parcunev et.al. 2012). The concentrations of yeast metabolites – aldehydes, esters and higher alcohols were measured according to (Marinov, 2010). Because of the limited volume of wort, the analyzes were performed on the 1, 3, 5, 7 and 9 day for the fermentation with top-fermenting yeast and on the 2, 4, 6, 8 and 10 day for the fermentation with bottom fermenting yeast. MATHEMATICAL MODELS AND THEIR EXPLANATION Equation of fermentation The fermentation with immobilized cells can be described with the equations for batch fermentation with free cells as previously reported (Parcunev et.al. 2012):

Modeling Of Alcohol Fermentation In Brewing - Carbonyl Compounds Synthesis And Reduction.

A mathematical model was developed for studying the carbonyl compounds synthesis and reduction in beer fermentation with alginate-chitosan microcapsules with liquid core. The model was based on the results for the influence of the fermentation temperature, original wort gravity and immobilized cells mass on the carbonyl compounds synthesis and reduction. The obtained model described with high accuracy the vicinal diketones synthesis and reduction and confirmed the experimental data. However, the model was not in agreement with the data for aldehydes synthesis and reduction. It did not take into account the second peak in aldehyde concentration during maturation. It can be assumed that the peak was related to maltotriose uptake by the used yeast strain. Nevertheless, the obtained model can be used for the description of carbonyl compounds synthesis and reduction in beer fermentation with immobilized cells.

Two approaches to multi–criteria optimisation of steel alloys for crankshafts production

The paper presents the application of multi–criteria optimisation to steel alloy composition determination aimed at obtaining improved properties material for crankshafts production. Neural network model of steel mechanical characteristics in dependence on amounts of its alloying elements was used for simulation purpose. Two optimisation approaches were applied to find optimal alloys composition. In the first one, several Pareto optimal solutions were found based on those obtained by simulation numerous compositions in the investigated region of interest. The second one used Taguchi method for robust design. The obtained optimal solutions were compared and decision about further production experiments was taken.

Multi-criteria optimization of steel alloys for crankshafts production

The paper presents application of multi-criteria optimization to steel alloy composition determination aimed at obtaining improved properties material for crankshafts production. Neural network model of steel mechanical characteristics in dependence on amounts of its alloying elements were used for simulation purpose. Then several Pareto optimal solutions were found based on obtained by simulation numerous compositions in the investigated region of interest.

Bio-ethanol production optimization using ACD with ESN critic

In the present paper on-line action-dependent heuristic neuro-dynamic programming was applied for optimization of a complex nonlinear production process. The approach is based on recurrent neural network architecture — Echo state network (ESN) — as critic network within the frame of adaptive critic design (ACD) scheme. The subject for optimization is bio-ethanol fermentation. The aim was to increase process productivity defining optimal dilution rate profile. The obtained by simulations results are good basis for further experimental investigations.