Optimiranje bioprocesnih parametrov proizvodnje etanola in kefirana z mikrobioto kefirnih zrn

doktorska disertacija

Katja Zajšek (Author), Andreja Goršek (Mentor), Irena Rogelj (Co-mentor)

Abstract

Doktorska disertacija je sestavljena iz dveh sklopov, ki obravnavata področje proizvodnje tradicionalnega kefirja s kavkaškimi kefirnimi zrni. Prvi je optimiranje bioprocesnih parametrov proizvodnje etanola med fermentacijo kefirja, drugi pa optimiranje proizvodnje kefirana v kefirnih zrnih. Uvodoma smo v disertaciji proučili vpliv časa aktivacije kefirnih zrn na spremembe vrednosti pH kefirja in na proizvodnjo etanola med fermentacijo kefirja. Upadanje pH vrednosti kefirja smo med 24 h fermentacijo uspešno opisali s predlaganim matematičnim, eksponentnim pH modelom. Poleg tega smo proučili vpliv časa aktivacije kefirnih zrn na zvezo med številom kvasovk v zrnih in kefirju in proizvedenim etanolom. Rezultati so pokazali, da zrna, ki jih aktiviramo dalj časa, vsebujejo večje število kvasovk in proizvedejo več etanola kot zrna, ki so aktivirana le nekaj dni. Število kvasovk v kefirju je z daljšanjem časa aktivacije zrn naraščalo. S kinetičnimi modeli, katerih razvoj je vzpodbudila povečana industrijska uporaba fermentacije, lahko opišemo rast mikroorganizmov, proizvodnjo produktov in porabo substratov tako v naravnih ekosistemih, kakor tudi pri določenih procesnih pogojih. Tako smo zne-strukturiranim matematičnim modelom opisali kinetične osnove proizvodnje etanola med šaržno fermentacijo kefirja. V ta namen smo proučili kinetiko rasti kefirnih zrn in proizvodnje etanola. Eksperimentalne podatke, pridobljene s serijo šaržnih fermentacij, izvedenih pri temperaturi 21 °C, začetni masni koncentraciji kefirnih zrn 42 g/L in izbranih časih fermentacije znotraj časovnega intervala (0-89) h, smo uporabili za ocenitev vrednosti kinetičnih parametrov in potrditev veljavnosti predlaganih sigmoidnih modelov. Rast kefirnih zrn smo opisali z logističnim modelom, proizvodnjo etanola pa z modificiranim Gompertzovim modelom. Ugotovili smo, da predlagana modela dobro opišeta kinetiko fermentacije kefirja glede na rast kefirnih zrn in proizvodnjo etanola in da se lahko uporabita za razvoj in optimizacijo bioloških procesov proizvodnje etanola. Nadalje smo razvili matematični model za kinetiko proizvodnje etanola med fermentacijo kefirja kot funkcijo temperature in časa. Vpliv temperature in časa fermentacije, na vrednost biokinetičnih parametrov proizvodnje etanola, smo opisali z modificiranim Gompertzovim modelom. Vrednost bioloških kinetičnih parametrov predlaganega modela smo ocenili z uporabo metode najmanjših kvadratov na podlagi eksperimentalnih podatkov, pridobljenih s serijo šaržnih fermentacij. Ocenili smo vpliv temperature na prirast biomase kefirnih zrn ter mikrobiološko sestavo kefirja in zrn. Temperaturno odvisnost maksimalne hitrosti proizvodnje etanola smo analizirali z uporabo Arrheniusove zveze, s katero smo ocenili vrednost aktivacijske energije za proizvodnjo etanola pri fermentaciji mleka s kefirnimi zrni, ki znaša 64,3 kJ/mol. Z razvitim matematičnim modelom lahko zelo dobro opišemo dinamiko proizvodnje etanola med fermentacijo kefirja. Prvi raziskovani sklop smo zaključili s proučevanjem vpliva časovnega presledka mirovanja mešala oz. pogostosti mešanja na proizvodnjo etanola in mikrobiološke lastnosti kefirja in kefirnega zrna. Razvili smo matematične zveze, ki opišejo razmerje med pogostostjo mešanja in (1) povečanjem prirasti kefirnih zrn v 24 h, (2) koncentracijskimi spremembami etanola med 24 h fermentacijo ter (3) pH vrednostjo kefirja po 24 h fermentaciji. Za razvite matematične modele so bile z uporabo metode najmanjših kvadrotov ocenjene vrednosti funkcijskih parametrov. Ocenili smo tudi vpliv pogostosti mešanja na število kvasovk, laktobacilov in mezofilnih MK kokov (pretežno laktokokov) v kefirju in zrnih po 24 h fermentaciji. Drugi sklop raziskav smo usmerili v raziskovanje bioprocesnih parametrov, ki vplivajo na proizvodnjo specifičnega eksopolisaharida (EPS) kefirana, značilnega za kefirna zrna.

Keywords

kefir;proizvodnja;kefirna zrna;kefiran;procesni parametri;optimiranje;fermentacija;etanol;črevesna mikrobiota;kvasovke;matematični modeli;disertacije;

Data

Language:	Slovenian
Year of publishing:	2012
Source:	[Maribor
Typology:	2.08 - Doctoral Dissertation
Organization:	UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher:	K. Zajšek]
UDC:	637.146.21:664.011(043.3)
COBISS:	16117526
Views:	3176
Downloads:	281
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Other data

Secondary language:	English
Secondary title:	Optimization of bioprocess parameters for ethanol and kefiran production using microbiota of kefir grains
Secondary abstract:	This doctoral dissertation consists of two parts that dealing with the production of traditional kefir with the Caucasus kefir grains. The first partdeals with the optimization of the bioprocess parameters of ethanol production during kefir fermentation and the second part deals with the optimization of kefiran production from kefir grains. As a start the effect of kefir grain activation time on the change in kefir pH value and the effect on the production of ethanol during kefir fermentation was studied. The drop in the pH value of kefir was successfully described during a 24 h fermentation process with the suggested mathematical, exponental pH model. Additionally, the effect of kefir grain activation on the relation between theproduced ethanol and the number of yeasts in the grains and in the kefir was examined. The results have shown that the more active grains produce more ethanol and contain a larger amount of yeasts in comparison with the grains that have been activated for only a few days. The number of yeasts in kefir was increasing in relation with the grain activation time. The kinetic models, increasingly developed because of the industrial use of fermentation, allow for a description of microbe growth, product creation and substrate use in natural ecosystems and under certain process conditions. Using a non-structured mathematical model the kinetic fundamentals of ethanol production during a batch fermentation of kefir were described. To that end the kinetics of kefir grain growth and ethanol production were examined. The experimental data, acquired through a batch fermentation series that was carried out at 21 °C, the start mass concentration of kefir grains 42 g/L and set fermentation times in the time bracket (0-89) h, was used to assess the kinetic parameter values and to confirm the validity of the suggested sigmoid models. The kefir grain growth was described using a logistic model. The ethanol production was described using a modified version of the Gompertz model. It was established that both models offer a good description of the kefir fermentation kinetics in relation to the kefir grain growth and ethanol production and that they can be used to develop and optimize the biologic processes of ethanol production. A mathematical model for ethanol production kinetics during kefir fermentation as a function of temperature and time was also developed. The influence of temperature and fermentation time on the value of the biokinetic parameters of ethanol production was described using the modified Gompertz model. The value of biological kinetic parameters of the suggested model were assessed using the method of least squares on the basis of the experimental data that was acquired through a batch fermentation series. The influence of temperature on the growth of kefir grain biomass and the microbiological composition of kefir and grains was assessed. The temperature dependence of the maximum speed of ethanol production was analysed using the Arrhenius equation that was used to assess the value of activation energy for the ethanol production during the fermentation of milk with kefir grains (64,3 kJ/mol.) This mathematical model allows for a very good description of the ethanol production dynamics during kefir fermentation.The first dissertation part was concluded by examining the effect of time lapses during the mixer inactivity or the stirring frequency on the ethanol production and the microbiological properties of kefir and kefir grains. Several mathematical equations were developed that describe the relation of the stirring frequency and (1) the increase of kefir grain growth in 24 h, (2) the concentration changes of ethanol during the 24 h fermentation and (3) pH value of kefir after the 24 h fermentation. The values of the function parameters for all developed mathematical models were estimated using the method of least squares.
Secondary keywords:	kefir;kefir grains;kefir grains microbiota;ethanol production;exopolysaccharide;kefiran production;process parameters;optimization;
URN:	URN:SI:UM:
Type (COBISS):	Dissertation
Thesis comment:	Univ. Maribor, Fak. za kemijo in kemijsko tehnologijo
Pages:	XXII, 123 str.
Keywords (UDC):	applied sciences;medicine;technology;uporabne znanosti;medicina;tehnika;agriculture and related sciences and techniques;forestry;farming;wildlife exploitation;kmetijstvo ter sorodne vede in tehnologije;produce of domestic (farmyard) animals and game;proizvodi domačih živali in divjadi;applied sciences;medicine;technology;uporabne znanosti;medicina;tehnika;chemical technology;chemical and related industries;kemijska tehnologija;kemijske in sorodne industrije;fundamentals of chemical engineering;osnove kemijskega inženirstva;
ID:	1026217