Novel hydrogel systems based on alginate and protein for controlled release of essential oils

[M. Volić]

110 str.

Tehnološko inženjerstvo - Biohemijsko inženjerstvo i biotehnologija / Technological engineering - Biochemical engineering and biotechnology

Etarska ulja predstavljaju smeše aromatičnih i lako isparljivih jedinjenja koja su poznata po svojim lekovitim svojstvima, zbog čega se mogu primeniti u lečenju raznih bolesti. Antimikrobna svojstva određenih vrsta etarskih ulja svrstavaju ih u alternativne izvore antimikrobnih lekova. Međutim, izazov koji se odnosi na stabilnost ovih ulja u toku proizvodnje i skladištenja ograničava njihovu širu primenu. Dodatno, usled promene pH vrednosti u gastrointestinalnom traktu može doći do gubitka biološke aktivnosti ulja. U skladu sa tim, velika pažnja se posvećuje zaštiti etarskih ulja u cilju obezbeđivanja njihove efikasnosti na mestu delovanja. U doktorskoj disertaciji prikazan je postupak pripreme novih hidrogel sistema na bazi alginata i proteina soje za inkapsulaciju i kontrolisano otpuštanje etarskog ulja timijana (Thymus vulgaris L.). Najpre je urađena karakterizacija emulzionih sistema, ispitivanjem stabilnosti, odnosno praćenjem promene zeta potencijala (laserska difrakciona tehnika), određivanjem reoloških svojstava emulzija, a zatim i analizom strukturne organizacije molekula na ulje/voda granici faza (Ramanova spektroskopija). U drugom delu rada sintetisani su hidrogel sistemi sa inkapsuliranim etarskim uljem, primenom tehnike elektrostatičke ekstruzije, a dodatno je urađena optimizacija postupka inkapsulacije variranjem koncentracija alginata i proteina soje (SPI). Zatim, ispitivani su dobijeni hidrogel sistemi u cilju određivanja interakcija između komponenata nosača, kao i nosača i inkapsuliranog ulja. Takođe, analizirani su profili bubrenja, veličina i oblik (optička mikroskopija) i površinska morfologija uzoraka (skenirajuća elektronska mikroskopija). Primenom metode kompresije testirana su mehanička svojstva hidrogel sistema, pri čemu je pokazano da povećanje koncentracija alginata i SPI ima pozitivan efekat na mehaničke karakteristike hidrogelova. Analizom uticaja temperature na hidrogel sisteme, u opsegu 50 - 100 ℃, uočeno je značajno povećanje termičke stabilnosti inkapsuliranog ulja. Hidrogelovi na bazi alginata i proteina su zatim ispitani u cilju procene efikasnosti inkapsulacije ukupnih polifenola (spektrofotometrijskom metodom) i timola (tečnom hromatografijom pod visokim pritiskom). Poseban deo rada posvećen je karakterizaciji sa aspekta potencijalne primene dobijenih sistema za kontrolisano otpuštanje etarskog ulja u simuliranim uslovima gastrointestinalnog trakta (pH, T, enzimi, soli), kao i analizi uticaja pomenutih uslova na reološko ponašanje hidrogelova. Takođe, određena je antioksidativna (ABTS i CUPRAC metode) i antimikrobna (mikrodiluciona metoda) aktivnost inkapsuliranog ulja. Treći deo rada obuhvata optimizaciju i karakterizaciju alginat/protein/lecitin sistema. Naime, sinergistički efekat proteina soje i lecitina na granici faza, potvrđen analizom stabilnosti emulzija, obezbedio je povećanje efikasnosti inkapsulacije i sporije otpuštanje timola usimuliranom želudačnom fluidu. Dodatno, mehanička i termička stabilnost hidrogel sistema su poboljšane dodatkom lipidnog emulgatora. Dobijeni rezultati ukazuju na veliki potencijal alginat/SPI i alginat/SPI/lecitin sistema za primenu u prehrambenoj i/ili farmaceutskoj industriji, sa posebnim akcentom na stabilnost i kontrolisano otpuštanje etarskog ulja.

Essential oils are mixtures of aromatic and highly volatile compounds, which are known for their healing properties, and therefore can be used to control infectious and non-infectious diseases. The antimicrobial properties of some essential oils classify them as alternative sources of antimicrobial drugs. However, the challenge regarding the stability of these oils during production and storage limits their wider use. In addition, changes in pH values in the gastrointestinal tract may lead to a loss of biological activity of oils. In recent years, increasing attention has been paid to the protection of essential oils in order to ensure their efficiency at the site of action. The presented doctoral thesis offers an approach for the formulation of novel hydrogel systems based on alginate and soy protein for encapsulation and controlled release of thyme essential oil (Thymus vulgaris L.). Firstly, the emulsion characterization was performed by examining the stability (Laser Difraction Techniques) and rheological characteristics of emulsions, as well as by analyzing the structural organization of molecules at the oil/water interface (Raman spectroscopy). In the second chapter of the dissertation, the hydrogel systems with encapsulated essential oil were synthetized using electrostatic extrusion technique. The encapsulation technique was further optimized using different concentrations of alginate and soy protein isolate (SPI). The hydrogels were characterized to show the interactions between carrier components and/or carrier-encapsulated oil (Fourier Transform Infrared spectroscopy). In addition, swelling behavior, particle size and shape (optical microscopy) and surface morphology (scanning electron microscopy) were analyzed. The particular emphasis was put on mechanical properties of hydrogels, where an increase in the concentration of alginate and soy protein had a positive impact on the mechanical properties of the hydrogel systems. The analysis of the temperature effect on hydrogel systems, in the range 50 - 100 ℃, showed a significant increase in the thermal stability of the encapsulated oil. Hydrogels based on alginate and protein were further tested for encapsulation efficiency of total polyphenols (spectrophotometric method) and thymol (liquid chromatography under high pressure). Subsequent analyses were focused on monitoring of the release kinetics in simulated conditions of the gastrointestinal tract (pH, T, enzymes, salts) and influence of the mentioned conditions on the rheological behavior of hydrogels. The antioxidant (ABTS and CUPRAC methods) and antimicrobial (microdilution method) activities of the encapsulated oil were also examined. The third chapter of the thesis was dedicated to the optimization and characterization of alginate/protein/lecithin systems. Namely, the synergistic effect of soy protein and lecithin on the interface, which was confirmed by analysis of emulsion stability, has improved carrierencapsulation efficiency and enabled slower release of thymol in the simulated gastric fluid. In addition, the mechanical and thermal stabilities of the hydrogels are improved by the addition of a lipid emulsifier. Overall, the results of this study indicate a great potential of alginate/SPI and alginate/SPI/lecitin systems for application in the food and/or pharmaceutical industry, with special emphasis on the stability and controlled release of oils in simulated conditions of the gastrointestinal tract.

inkapsulacija, etarsko ulje timijana (Thymus vulgaris L.), alginat, proteini soje, lecitin, hidrogel sistemi, kontrolisano otpuštanje

encapsulation, thyme essential oil (Thymus vulgaris L.), alginate, soy proteins, lecithin, hydrogel systems, controlled release

665.3:544.773.432(043.3)

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