Isolation and characterisation of flavonoids from citrus peels : doctoral dissertation
Izolacija in karakterizacija flavonoidov iz lupin citrusov : doktorska disertacija

english

doktorska dela

2013

citrus peels   conventional extraction   favonoids   membrane separation processes   Taguchi experimental design

Univerza v Mariboru, Fakulteta za kemijo in kemijsko tehnologijo

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 solventratio 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.

07.08.2023