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Influence of process parameters on the extraction of flavanones from mandarin peel
Katja Makovšek, Željko Knez, Mojca Škerget, 2012, original scientific article

Abstract: Flavanones are an important group of flavonoids that are characteristic for citrus. In the present work isolation of flavanones from mandarin peel was performed by conventional extraction using water, ethanol, acetone and aqueous solutions of acetone and ethanol. The extracts were analysed on the content and composition of flavanones. Furthermore the DPPH radical scavenging activity of extracts was determined. Finally, the influence of extraction parameters (particle size, extraction temperature, extraction time,material to solvent ratio, number of extraction stages and type of solvent) on the yield and the efficiency of extraction were determined by Plackett-Burman experimental design. The results showed that 70% aqueous solution of acetone was the most efficient solvent for isolation of flavanones from mandarin peel. The main flavanones present in the obtained extracts were hesperidin (HES) and narirutin (NRT). The number of extraction stages influenced the yield of extraction, type of solvent influenced the hesperidin extraction efficiency and particle size of material influenced the narirutin extraction efficiency.
Keywords: conventional extraction, mandarin peel, flavanone, hesperidin, narirutin, Plackett-Bauman experimental design
Published: 10.07.2015; Views: 681; Downloads: 22
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Isolation and Characterisation of Flavonoids From Citrus Peels
Katja Makovšek, 2013, doctoral dissertation

Abstract: 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.
Keywords: Flavonoids, hesperidin, naringin, citrus peels, mandarin (Citrus reticulata), pommelo (Citrus maxima), conventional extraction, supercritical fluid extraction, membrane separation processes, Taguchi experimental design
Published: 22.04.2013; Views: 2509; Downloads: 278
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Extraction of lutein diesters from tagetes erecta using supercritical $CO_2$ and liquid propane
Mojca Škerget, Miran Bezjak, Katja Makovšek, Željko Knez, 2010, original scientific article

Abstract: The efficiency of high pressure extraction of lutein diesters from marigold (Tagetes erecta) flower petals has been investigated. The solvents used for extraction were supercritical carbon dioxide and liquid propane. Operating parameters were 300 bar and 40, 60 and 80 °C for $CO_2$ and 100, 150, 200 bar and 40 and 60 °C for propane, respectively. The influence of process parameterson the total yield of extraction and content of lutein diesters in the extracts was investigated. The results show, that solvent power of propanefor lutein diesters is approximately 3.5 times higher than of $CO_2$. The calculation procedure based on the Fick's second law was applied to determine the diffusivities of lutein diesters during extraction from marigold flower petals for both extraction stages: a constant rate stage followed by a stage of decreasing rate. The mathematical model based on the Fick's second law well described the experimental extraction results.
Keywords: lutein diesters, Tagetes errecta, extraction, supercritical $CO_2$, subcritical propane
Published: 10.07.2015; Views: 619; Downloads: 33
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Kinetične študije hitrosti rasti kefirnih zrn : diplomska naloga
Katja Zajšek, 2006, undergraduate thesis

Keywords: kefirna zrna, kinetika, kinetični parametri, šaržni bioreaktor
Published: 26.07.2007; Views: 3285; Downloads: 0

In-situ investigation of sucrose hydrolysis - successful link between design of experiment, RC1 and reactIR system
Katja Zajšek, Andreja Goršek, 2008, original scientific article

Abstract: 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 Keywords: sucrose hydrolysis, catalyst, Taguchi method, in-situ FTIR, reaction calorimeter RC1
Published: 31.05.2012; Views: 1309; Downloads: 20
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Katja Zajšek, 2012, doctoral dissertation

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 z ne-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. Dokazali smo, da lahko z vodenjem procesnih pogojev gojenja zrn v mleku (temperatura, vrtilna frekvenca mešala) in sestavo fermenta
Keywords: kefir, kefirna zrna, mikrobiota kefirnih zrn, proizvodnja etanola, eksopolisaharidi, produkcija kefirana, procesni parametri, optimiranje
Published: 13.07.2012; Views: 2527; Downloads: 218
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