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1.
Razvoj in optimizacija HPLC metode za določanje antimikrobnih substanc v suhem ekstraktu limone
Klara Žvab, 2021, magistrsko delo

Opis: Hesperidin, eriocitrin, rutin ter kavna in klorogena kislina so antimikrobne snovi, ki jih najdemo v limoni in njenem suhem ekstraktu. Zaradi njihovih pozitivnih učinkov, predvsem na zdravje ljudi, se vse bolj pogosto uporabljajo v raznih prehrambenih dodatkih. V magistrskem delu smo razvili in optimizirali HPLC metodo, s katero identificiramo in kvantificiramo te antimikrobne snovi v suhem ekstraktu limone. Za ločevanje spojin smo uporabili gradientno elucijo, kjer smo 0,4 % ocetni kislini postopoma dodajali vse več organske faze (metanola) pri pretoku 0,8 ml/min. Komponente v ekstraktu smo identificirali s primerjavo UV spektrov in retenzijskih časov referenčnih substanc, vsebnost komponent pa smo določili na podlagi umeritvene krivulje. Pokazali smo linearnost metode za določevanje klorogene kisline, eriocitrina in hesperidina v območju 2,5–300 g/ml, kavne kisline v območju 1,0–300 g/ml in rutina v koncentracijskem območju 5,0–300 g/ml. Določili smo mejo zaznave (LOD), ki za vse komponente znaša 1,0 g/ml ter mejo določljivosti (LOQ), ki je 2,5 g/ml za hesperidin, eriocitrin in klorogeno kislino, 1,0 g/ml za kavno kislino ter 5,0 g/ml za rutin. Rezultati kažejo, da je metoda natančna za določevanje vseh komponent, medtem ko je točna za določevanje hesperidina in kavne kisline. Z optimizirano metodo smo določili vsebnost posameznih antimikrobnih komponent v različnih vzorcih ekstrakta limone. Vse komponente smo zaznali v liofiliziranem suhem ekstraktu limone, v katerem sta prevladovala hesperidin (7,09 mg/g ekstrakta) in eriocitrin (3,81 mg/g ekstrakta). Visoke vsebnosti hesperidina smo zaznali tudi v liofiliziranem ekstraktu limete, kjer je ta vrednost znašala 9,74 mg/g ekstrakta. Ostale komponente so bile v teh in ostalih vzorcih zaznane v manjših količinah, nekje od 0,15 do 2,5 mg komponente/g ekstrakta.
Ključne besede: tekočinska kromatografija visoke ločljivosti (HPLC), validacija, hesperidin, eriocitrin, rutin, kavna kislina, klorogena kislina
Objavljeno: 20.01.2021; Ogledov: 199; Prenosov: 37
.pdf Celotno besedilo (5,31 MB)

2.
Influence of process parameters on the extraction of flavanones from mandarin peel
Katja Makovšek, Željko Knez, Mojca Škerget, 2012, izvirni znanstveni članek

Opis: 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.
Ključne besede: conventional extraction, mandarin peel, flavanone, hesperidin, narirutin, Plackett-Bauman experimental design
Objavljeno: 10.07.2015; Ogledov: 979; Prenosov: 43
.pdf Celotno besedilo (231,88 KB)
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3.
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: 2898; Prenosov: 385
.pdf Celotno besedilo (10,49 MB)

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