Georgi Kostov

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.

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):

Chemical Composition and Antimicrobial Activity of Essential Oils from Black Pepper, Cumin, Coriander and Cardamom Against Some Pathogenic Microorganisms

Abstract Four popular spices black pepper (Piper nigrum L.), cumin (Cuminum cyminum L.), coriander (Coriandrum sativum L.) and cardamom (Elettaria cardamomum) were analyzed for their oil composition by GC-MS. Thirty compounds were identified in the black pepper oil and the main components were β-caryophyllene (20.225 %), sabinene (18.054 %), limonene (16.924 %), α-pinene (9.171 %) and α-phellandrene (5.968 %). Twenty five compounds were identified in the cumin oil – cuminaldehyde (30.834 %), 3-caren-10-al (17.223 %), β-pinene (14.837 %), γ–terpinene (11.928 %), 2-caren-10-al (8.228 %) and pcymene (6.429 %). Twenty nine compounds were identified in the coriander oil – β-linalool (58.141 %), α-pinene (8.731 %), γ-terpinene (6.347 %) and p-cymene (5.227 %). Twenty nine compounds were identified in the cardamom oil – α-terpinyl acetate (39.032 %), eucalyptol (31.534 %), β-linalool (4.829 %), sabinene (4.308 %) and α-terpineol (4.127 %). The antimicrobial activity of essential oils against pathogenic (Escherichia coli ATCC 25922, Escherichia coli ATCC 8739, Salmonella sp. (clinical isolate), Staphylococcus aureus ATCC 6538P, Proteus vulgaris G) microorganisms by disc-diffusion method was examined. Gram-positive bacteria were more sensitive to the oils (inhibition zones being between 8 and 12.5 mm) and the minimum inhibitory concentration was more than 600 ppm; Gram-negative bacteria were less sensitive. The obtained essential oils are suitable for use as biopreservative agents.

Encapsulation of brewing yeast in alginate/chitosan matrix: lab-scale optimization of lager beer fermentation

Two mathematical models were developed for studying the effect of main fermentation temperature (TMF), immobilized cell mass (MIC) and original wort extract (OE) on beer fermentation with alginate-chitosan microcapsules with a liquid core. During the experiments, the investigated parameters were varied in order to find the optimal conditions for beer fermentation with immobilized cells. The basic beer characteristics, i.e. extract, ethanol, biomass concentration, pH and colour, as well as the concentration of aldehydes and vicinal diketones, were measured. The results suggested that the process parameters represented a powerful tool in controlling the fermentation time. Subsequently, the optimized process parameters were used to produce beer in laboratory batch fermentation. The system productivity was also investigated and the data were used for the development of another mathematical model.

Kinetics of Batch Fermentation in the Cultivation of a Probiotic Strain Lactobacillus Delbrueckii Ssp. Bulgaricus B1

Abstract A comparative study of kinetic models to describe the dynamics of the fermentation process of culturing of a probiotic strain Lactobacillus delbrueckii ssp. bulgaricus B1 was performed. The models of Monod, Aiba, Tiessier, Hinshelwood and the equation of the logistic curve combined with the model of Ludeking-Piret were used. It has been found that the different models described the observed fermentation dynamics differently. The conducted comparative study demonstrated that the models of Monod and the equation of the logistic curve combined with the model of Ludeking-Piret were suitable for the description of the fermentation dynamics. The mathematical models showed no significant product and/or substrate inhibition. The culture developed with a low specific growth rate, but nevertheless it accumulated 1012-1013 viable cells. The substrate was absorbed primarily from cells in the stationary growth phase rather than cells in the exponential growth phase

Modeling Of Oxygen Effect On Kinetics Of Batch Fermentation Process For Yogurt Starter Culture Formation

The aim of this work is to describe the kinetics of yogurt starter culture production by S.thermophilus 13 and Lb. bulgaricus 2-11 and to quantitatively analyse the effect of different dissolved oxygen concentration in the milk on the process trend. Five different mathematical models for description of process kinetics are tested and the best one is selected. The increase of initial concentration of dissolved oxygen leads to a proportional decrease in the specific growth rate of the population and of the rates of lactose consumption and lactic acid production. On the basis of this investigations, two zones of initial dissolved oxygen concentration are defined. In each of these zones, the associated pair of microorganisms have different behaviour.

New Approach To Modelling The Kinetics Of The Fermentation Process In Cultivation Of Lactic Acid Bacteria.

The present paper reviews the methods for assessing the kinetics of the fermentation process for the cultivation of probiotic strains of lactic acid bacteria in a laboratory bioreactor with stirring. To describe the kinetics of the lactic acid fermentation process, an alternative approach with the use of semi-empirical degree laws that offer a new look into the biological parameters in the description models is proposed.

Optimization of Conditions for Obtaining Alginate/Olive Oil Capsules for Application in Dairy Industry

Abstract Encapsulation is a process of incorporation of bioactive substances in a specific matrix. It results in increasing and/or maintaining of the biological agent concentration in the food matrix or the fermentation system. The encapsulation process is influenced by various factors. The aim of the present work was to investigate the influence of alginate type and concentration, homogenization rate and the oil phase amount in the preparation of capsules rich in olive oil. It has been found that emulsions obtained with medium viscosity alginate were characterized by better stability. To establish the joint influence of the factors was used screening design experiment, the optimization features selected being temperature, centrifugal and microscopic stability. The optimal levels of the factors were established and they we applied for capsule preparation. The obtained capsules showed maximum stability and possibility to be used in dairy product manufacture.

Modeling Of Continuous Ethanol Fermentation In Ideal Mixing Column Bioreactor.

A method for formalization and analytical determination of the kinetic parameters of continuous alcohol fermentation in a reactor and in a cascade of reactors with ideal mixing was discussed in the present work. A fluidized bed bioreactor with immobilized yeast with elucidated structure of the flows was used. The method of formalization of the process kinetics involved two steps – determination of the optimal dilution rate of a continuous fermentation process, and determination of the total kinetic parameters of the cascade of reactors, including the minimum number of steps that can ensure production of maximum ethanol yield in the system.

Encapsulation of plant and animal oils used in dairy industry: A review

Abstract The development of new food products enriched with biologically active components is a topical issue for modern food science and practice. Many of these substances are unstable when being incorporated into the food matrix, which demands a study on the possibilities to stabilize them before use. Encapsulation of biologically active substances is a method which provides stability of the substance in the food product. The principles for implementing encapsulation of biologically active substances, especially natural oils, the matrices and the encapsulation methods are discussed in the present review. Data on the impact of key process parameters of encapsulation, the biological value of oils and the opportunities for application of the encapsulated systems in different groups of dairy products are presented.