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EKSPERIMENTALNO DOLOČANJE VPLIVA PROCESNIH PARAMETROV PROIZVODNJE KEFIRNIH ZRN S STATISTIČNO METODO
Aleksander Rauter, 2009, diplomsko delo

Opis: V diplomskem delu opisujemo eksperimentalni potek določanja optimalnih procesnih parametrov za proizvodnjo kefirnih zrn in določitev prispevka posameznih procesnih parametrov pri optimalnih rastnih pogojih za kefirna zrna. Vse poizkuse smo opravljali v laboratorijskem šaržnem reaktorju (reakcijski kalorimeter RC1e). Sledeč strokovni literaturi smo za optimizacijske parametre izbrali temperaturo rastnega medija, masno koncentracijo glukoze in kvasa, ter vrtilno frekvenco mešala. S pomočjo Taguchi-jeve metode smo načrtovali parcialni faktorialni eksperiment z navedenimi optimizacijskimi kriteriji. Vsak poizkus je potekal 24 ur. Eksperimentalne rezultate smo obdelali z analizo variance, s katero smo pri idealnih rastnih pogojih kefirnih zrn določili prispevek posameznih optimizacijskih kriterijev. V drugem delu eksperimentalnega dela smo preverili še vpliv različnih vrst kravjega mleka na prirast kefirnih zrn pri zgoraj določenih optimalnih pogojih. V strokovni literaturi smo glede tega zasledili le študije odvisnosti prirastka kefirnih zrn od vsebnosti mlečnih maščob. Rezultatov teh ugotovitev z našimi eksperimenti nismo mogli potrditi.
Ključne besede: kefir, kefirno zrno, optimiranje rasti, Taguchi-jeva metoda, procesni parametri
Objavljeno: 22.12.2009; Ogledov: 2174; Prenosov: 188
.pdf Celotno besedilo (1,49 MB)

4.
Quantitative examination of process parameters during kefir grain biomass production
Andreja Goršek, Marko Tramšek, 2007, kratki znanstveni prispevek

Opis: This article examines the propagation of kefir grains in fresh HTP whole fat cows' milk, with some additions (glucose and bakers yeast). The objective of our work was an experimental determination of the various process parameters relative influence on the propagation and daily kefir grain increase mass, using the Taguchi method for experimental design. The effects of medium temperature, glucose mass concentration, bakers yeast mass concentration and the rotational frequency of the stirrer at four levels were studied. Orthogonal array layout of L16 was selected for the proposed experimental design. All experiments were performed in an automated laboratory reaction calorimeter RC1 (Mettler-Toledo) with the same milk (3.5 % fat). The gravimetric method was used to determine daily kefir grain mass increases. Relative contributions of the proposed influencing process parameters on the daily kefir grains increase mass were estimated by analysis of the variance (ANOVA). The highest increase (51.5 %) was found at the rotational frequency of the stirrer 90 (1/min), at glucose mass concentration 20 g/L, and at mediumtemperature 24 °C. Within the observed range of yeast mass concentrationthis process parameter was found to be insignificant compared to others. The rotational frequency of the stirrer has the highest relative influence on the daily kefir grains increase mass (37.3 %) while glucose mass concentration and medium temperature have lower ones, 18.8 % and 9.9 %, respectively. The remaining fraction represents error influence. The main reason for its relatively high value (34.0 %) is that kefir grains are bulky and awkward to handle. This fact confirms the importance of optimal kefir grains production management.
Ključne besede: chemical processing, milk products, kefir, kefir grain growth, process parameters, design of experiments, Taguchi method, RC1
Objavljeno: 31.05.2012; Ogledov: 1531; Prenosov: 30
URL Povezava na celotno besedilo

5.
Determination of the process parameters relative influence on k[sub]La value using Taguchi design methodology
Marko Tramšek, Andreja Goršek, 2007, izvirni znanstveni članek

Opis: This article describes experimental determination of the relative impact of significant process parameters that influence volumetric oxygen mass transfer coefficient (kLa) using Taguchi design methodology. For this purpose an automated RC1 reaction calorimeter (Mettler-Toledo), which was originally developed for chemical processes, was modified for the bioprocesses. Simple fermentation using Baker's yeast was studied to illustrate the design procedure. Orthogonal array L25 was selected for the proposed design and ANOVA method was used for recognizing the relative influence of the process parameters. Within the observed range of temperature (?), fermentation media volume (VFM), and yeast mass concentration (?Y), these process parameters were found to be unimportant compared to the volumetric air flow rate (qV,a) and rotational frequency of the stirrer (fm). The qV,a had a substantial effect on the kLa value (89.2 %) and the fm had just a small one (3.6 %), meanwhile the remain fraction to 100 % represents error. The results refer strictly to the selected case study. Anyhow, the proposed procedure shows that application of the Taguchi approach for analyzing the oxygen mass transfer based on the experimental data obtained from a highly-automated laboratory reactor appears to have potential usage in general biopharmaceutical process design.
Ključne besede: bioprocess parameters, mass transfer, volumetric oxygen mass transfer coefficient, process parameters, Taguchi method, analysis of variance
Objavljeno: 31.05.2012; Ogledov: 1416; Prenosov: 20
URL Povezava na celotno besedilo

6.
In-situ investigation of sucrose hydrolysis - successful link between design of experiment, RC1 and reactIR system
Katja Zajšek, Andreja Goršek, 2008, izvirni znanstveni članek

Opis: The main purpose of this work was combining the modern laboratory equipment (RC1 reaction calorimeter and ReactIRTMiC10 reaction analysis system) and the concept of the Taguchi fs design of experiment to determine the relative influence of important process parameters affecting the sucrose hydrolysis. The reaction was catalyzed by strong acidic cation-exchange resin Amberlite IR-120 in H+ form. Four process parameters, including reaction temperature (.), sucrose mass concentration (fÁS), catalyst mass concentration (fÁC) and the rotational frequency of the stirrer (fm) at four levels were considered in this study. Relative contributions of the proposed influencing process parameters on hydrolysis time were estimated by analysis of the variance (ANOVA). The results showed that . had a substantial effect on the reaction time (78,3 %), the fm and fÁC had a smaller ones (7,9 % and 6,4 %, respectively), meanwhile the remain fraction to 100 % represents error (7,4 %). The optimum conditions, where the time required for complete sucrose hydrolysis would be the shortest, are: .= 79 Ključne besede: sucrose hydrolysis, catalyst, Taguchi method, in-situ FTIR, reaction calorimeter RC1
Objavljeno: 31.05.2012; Ogledov: 1200; Prenosov: 15
URL Povezava na celotno besedilo

7.
Optimization of extrusion process by genetic algorithms and conventional techniques
Zoran Jurković, Miran Brezočnik, Branko Grizelj, Vesna Mandić, 2009, izvirni znanstveni članek

Opis: The purpose of this research is the determination of the optimal cold forward extrusion parameters with the minimization of tool load as objective. This paper deals with different optimization approaches in order to determine optimal values of logarithmic strain, die angle and friction factor with the purpose to find minimal tool loading obtained by cold forward extrusion process. Two experimental plans based on factorial design of experiment and orthogonal array have been carried out. Classical optimization, according to the response model of extrusion forming force, and the Taguchi approach are presented. The obtained extrusion force model as the fitness function was used to carry out genetic algorithm optimization. Experimental verification of optimal forming parameters with their influences on the forming forces was also performed. The experimental results show an improvement in the minimization of tool loading. The results of optimal forming parameters obtained with different optimization approaches have been compared and based on that the characteristics analysis (features and limitations) of presented techniques.
Ključne besede: metal forming, forward extrusion force optimization, design of experiments, Taguchi approach, genetic algortihm
Objavljeno: 31.05.2012; Ogledov: 992; Prenosov: 46
.pdf Celotno besedilo (469,47 KB)
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8.
Experimental design of crystallization processes using Taguchi method
Miran Hvalec, Andreja Goršek, Peter Glavič, 2004, izvirni znanstveni članek

Opis: Crystallization has become one of the most important unit operation in the chemical industries. The need to reduce the time from product discovery to market introduction is an inherent concern. In order to achieve the prescribedproduct quality characteristics, the process of engineering experimentation has to be optimized. Therefore, an experimental design method for crystallization processes is presented in this paper. Initially, the standardized Taguchi method was used to plan a minimum number of experiments. After identifying the working levels of the design factors and the main performance characteristics of the product under study, the method can be successfully applied to the crystallization processes. The simultaneous variations of the main crystallization parameters and their interactions were investigated using orthogonal array technique. A statistical analysis of 'signal-to-noise' ratio was followed by performing a variance analysis. After developing some special criteria, which depend on performance objectives, the optimal levels of the design factors were determined. Crystallization of $KNO_3$ with desirable particle size as a performance characteristic was used to illustrate the design procedure. The effects of rotational frequency of the stirrer, linear cooling rate and added admixture on final particle size were studied. In order to keep the selected parameters constant during the experiment and to ensure reproduction of entire experiment the automated reaction calorimeter RC1 was used.
Ključne besede: crystallization, particle size, Taguchi method
Objavljeno: 01.06.2012; Ogledov: 1236; Prenosov: 43
.pdf Celotno besedilo (701,22 KB)
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9.
ŠTUDIJ VPLIVA PROCESNIH POGOJEV NA HIDROTERMIČNE REAKCIJE ODPADNE BIOMASE PRI PREDELAVI OLIV S TAGUCHI METODO
Tjaša Sternad, 2012, diplomsko delo

Opis: Olivna biomasa predstavlja vredno surovino za integrirano proizvodnjo baznih kemikalij, goriv in energijo. S pomočjo hidrotermičnih procesov, ki temeljijo na uporabi subkritične vode, smo biomaso pretvorili v različne produkte. Hidrotermične reakcije smo izvajali v HP/HT šaržnem reaktorju. V prvem delu raziskav nas je zanimala sestava olivne biomase (oljčne tropine). Sestavo biomase smo določili po NREL metodah. Določili smo odstotni delež ekstraktivnih snovi, lignina in ogljikovih hidratov ter s pomočjo HPLC določili strukturne ogljikove hidrate. Načrt izvajanja eksperimentov smo pripravili s pomočjo Taguchi metode, ki nam je omogočil minimalno število eksperimentov, glede na število procesnih parametrov in število nivojev. Eksperimentalni rezultati so bili izhodišče za analizo vpliva na izkoristek vodotopnih in aceton topnih produktov, ter na lastnosti in sestavo vodotopne frakcije. Z uporabo spektrofotometrijskih metod smo vodotopnemu ekstraktu določili vsebnost totalnih fenolov, totalnih flavonoidov, taninov ter antioksidativno aktivnost. Načrtovanim eksperimentom smo določili vpliv posameznih procesnih pogojev (temperatura, tlak, razmerje topilo/tropine, dodatek katalizatorja in reakcijski čas) na potek hidrotermične reakcije odpadne olivne biomase. Tega smo se lotili z grafično in statistično analizo ANOVA. Teoretično smo določili optimalne pogoje, ter jih preverili z dodatnimi eksperimenti pri optimalnih pogojih.
Ključne besede: olivna biomasa, hidrotermična reakcija, subkritična voda, izkoristek, totalni fenoli, totalni flavonoidi, tanini, antioksidativna aktivnost, Taguchi metoda, procesni parametri, optimalni pogoji, ekstraktivne snovi, lignin, ogljikovi hidrati.
Objavljeno: 04.10.2012; Ogledov: 1253; Prenosov: 140
.pdf Celotno besedilo (2,16 MB)

10.
Isolation and Characterisation of Flavonoids From Citrus Peels
Katja Makovšek, 2013, doktorska disertacija

Opis: Citrus flavonoids are very interesting for food and pharmaceutical industry since they possess many antioxidant properties and biological activities. Mandarin peels represent an important source of hesperidin and polymethoxy flavones nobiletin and tangeretin. Pommelo peels represent an important source of naringin that can be used as precursor for naringin dihdydro-2,3-chalcone artificial sweetener. Since pommelo peels possess good antioxidant and antimicrobial properties, their extracts are very interesting products for food industry. Therefore isolation of flavonoid from mandarin and pommelo peels is an important topic of investigations. The investigation of the doctoral dissertation is divided in four parts. The first part is focused on the determination of the optimal conditions for the isolation of hesperidin and naringin from mandarin and pommelo peels by conventional extraction. The optimal conditions and the influence of extraction parameters are determined by Taguchi methodology. Very good isolation efficiency of hesperidin, 61.3 mg HES from 1 g of mandarin peels, was obtained by 70 % acetone solution and extraction conditions: 60 °C, 90 min, material to solvent ratio 1/50 g/mL and 3 stages of extraction. The highest amount of naringin, 32.8 mg NAR were isolated from 1 g of material at conditions: conventional extraction, 120 min, albedo, 60 % ethanol, material to solvent ratio 1/50 g/mL and 60 °C. The simple procedure of conventional extraction shows results comparable to more sophisticated methods such as extraction with microwave and ultrasound. Taguchi experimental design was proved to be an efficient methodology to determine the optimal conditions and the parameters that significantly influence product properties. The second part of the investigation focuses on the characterization of mandarin and pommelo peel extracts and their antioxidant properties. Radical scavenging activity against DPPH and antioxidant capacity of lipid soluble and water soluble compounds were determined for mandarin and pommelo extracts. Taguchi experimental design was applied for determination of the influence of extraction parameters on antioxidant properties. The optimal conditions to prepare extracts with high antioxidant properties were also determined. In the third part the investigation focuses on the concentration and separation of citrus flavonoids by extraction with supercritical fluids. Supercritical CO2 was applied for the separation of polymethoxylated flavones (PMF) and flavanone glycoside from mandarin peels. The optimal conditions and the parameter influence on the separation were determined by using Taguchi experimental design. The influence of supercritical fluid extraction parameters on material pre-treatment and isolation of flavonoids was studied. These investigations show that supercritical CO2 is a potential solvent for isolation and separation of PMF from mandarin peels. The fourth and last part of the investigation focuses on the concentration of flavonoids in extract solutions. Since membrane separation processes are very interesting concentration methods in industry, microfiltration, ultrafiltration, nanofiltration and revese osmosis were used for concentration of mandarin and pommelo peel extract solutions. Microfiltration and ultrafiltration could be used in the separation steps after extraction, since they did not influence the amount of dry material and valuable compounds in tested solutions. Reverse osmosis and nanofiltration were shown as useful methods for separation of solvent from extract solutions.
Ključne besede: Flavonoids, hesperidin, naringin, citrus peels, mandarin (Citrus reticulata), pommelo (Citrus maxima), conventional extraction, supercritical fluid extraction, membrane separation processes, Taguchi experimental design
Objavljeno: 22.04.2013; Ogledov: 2345; Prenosov: 196
.pdf Celotno besedilo (10,49 MB)

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