doctoral dissertation
Kaja Jeromel (Author), Maja Leitgeb (Mentor), Mateja Primožič (Co-mentor)

Abstract

Naraščajoč problem protimikrobne rezistence (AMR) zahteva iskanje novih, alternativnih ter varnih protimikrobnih sredstev, pridobljenih iz naravnih virov, ki bi z različnimi mehanizmi omogočili učinkovito zaviranje rasti mikroorganizmov. V ta namen smo se v sklopu doktorske disertacije sprva osredotočili na pridobivanje protimikrobno učinkovitih ekstraktov iz koščic avokada (ASE), ki so neužitne ter jih tretiramo kot odpadno biomaso, po drugi strani pa predstavljajo bogat vir biološko aktivnih spojin. Ker ekstrakcijska metoda ter topilo izjemno vplivata na vsebnost ter encimsko, antioksidativno in protimikrobno aktivnost pridobljenih ASE, smo primerjali učinkovitost ultrazvočne (UE) ter Soxhlet (SE) ekstrakcije, z bolj zeleno in trajnostno naravnano ekstrakcijo s superkritičnimi fluidi (SFE). Visoke vsebnosti izbranih fenolnih spojin v ASE so pripomogle k dobremu antioksidativnemu ter protimikrobnemu potencialu testiranih ASE, ki so zavirali rast kar 13 od 15 testiranih mikroorganizmov z izjemno nizkimi vrednostmi minimalnih inhibitornih koncentracij (MIC). ASE, pridobljen s SFE, je izkazal najvišjo vsebnost totalnih fenolov in proteinov, vseboval je 12 od 14 izbranih fenolnih spojin. Vseboval je tudi vse proučevane encime z visoko aktivnostjo ter bil najbolj učinkovit pri zaviranju rasti testnih mikroorganizmov. Za nadaljnjo uporabo ASE je pomembna tudi njihova inkorporacija v biokompatibilen, netoksičen ter mehansko primeren nosilec, ki omogoča nadzorovano in trajno sproščanje biološko aktivnih spojin. Nanoceluloza (NC) s svojimi lastnostmi predstavlja velik potencial kot funkcionalni nosilec, zato je v nadaljevanju doktorske disertacije predstavljena sinteza NC materialov in njenih hibridov s protibakterijskim delovanjem. Z optimizacijo postopka biosinteze iz bakterij rodu Komagataeibacter smo pripravili bakterijsko nanocelulozo (BNC) v obliki membran in kroglic ter proučili njihovo morfologijo ter kemijsko sestavo. Ugotovljeno je bilo, da tako izbor bakterijskega seva kot pogoji gojenja pomembno vplivajo na produktivnost, obliko, lastnosti in kakovost BNC. K. xylinus predstavlja sev bakterij, ki zagotavljajo hitro (3 dni) in visoko produktivnost (do 518,4 g/L) kristalinične (80,56 %) BNC v obliki membran in kroglic. Sledila je priprava funkcionaliziranih nanoceluloznih hibridov z ASE za namene protibakterijskega delovanja in možne uporabe sintetiziranih hibridov kot oblog pri celjenju ran. V ta namen so bili ASE inkorporirani v dva različna tipa NC materialov, BNC in nanofibrilirano celulozo (CNF). Proučevana je bila njihova morfologija, kemijska sestava ter sproščanje ASE iz NC nosilcev. Izvedli smo tudi študijo protibakterijske učinkovitost nanoceluloznih hibridov z ASE proti Escherichia coli in Staphylococcus aureus, bakterijama povezanima s kožnimi boleznimi in AMR. Določitev hidrodinamične velikosti delcev, zeta potenciala ter indeksa polidisperznosti ASE je omogočila dodatno razlago možnih mehanizmov protibakterijske aktivnosti. Biohibrid BNC, modificirana z ASE, je izkazala odlično bakteriostatično in baktericidno aktivnost, s sposobnostjo adsorpcije visokih koncentracij ASE (do 72,89 mg na kroglico in do 46,61 mg na 1 cm2 membrane). Biohibridi BNC/ASE predstavljajo sinergistični sistem, v katerem BNC zagotavlja ustrezen desorpcijski kinetični profil, da omogoči sproščanje protibakterijskih učinkovin ASE. Prav tako pa visoka stopnja nabrekanja in lastnost zadrževanja vode izkazujeta primernost biohibridov za različne aplikacije povezane z regenerativno medicino kože in celjenjem ran. CNF, modificirana z ASE (do 14,2 mg na 1 cm2 filma), je prav tako izkazala izjemne protibakterijske lastnosti (do 100 % redukcija z log R do 5,64), primerljive s CNF filmi, modificiranimi z antibiotikom klindamicinom (do 100 % redukcija z log R do 6,50). Študija kinetike sproščanja ASE je prikazala odzivnost CNF filmov na različna pH okolja (pH 7,4 in 5,5), kar izkazuje dodaten potencial ter možen pozitiven učinek pri celjenju ran.

Keywords

avokado;ekstrakcija;nanoceluloza;protimikrobna aktivnost;dostava zdravil;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher: [K. Kupnik]
UDC: 544.4:66.094.25(043.3)
COBISS: 209446147 Link will open in a new window
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Downloads: 5
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Other data

Secondary language: English
Secondary title: Synthesis of functionalized nanocellulose hybrids with avocado (Persea americana) extracts with antibacterial activity
Secondary abstract: The ever-growing problem of antimicrobial resistance (AMR) requires the search for new, alternative and safe antimicrobial agents obtained from natural sources, which would enable the effective growth inhibition of the microorganisms. Therefore, as part of the doctoral dissertation, we initially focused on obtaining antimicrobially active extracts from inedible avocado seeds (ASE), which represent a rich source of biologically active compounds. Since the extraction method and the solvent greatly affect the content and enzymatic, antioxidant and antimicrobial activity of the obtained ASE, the efficiency of the more well-known ultrasonic (UE) and Soxhlet (SE) extraction with the greener and more sustainable supercritical fluid extraction (SFE) was compared. The high content of selected phenolic compounds in ASE contributed to the good antioxidant and antimicrobial potential of the ASE, which inhibited the growth of as many as 13 out of 15 tested microorganisms with extremely low minimum inhibitory concentration (MIC). ASE obtained by SFE showed the highest content of total phenols and proteins, contained 12 of 14 selected phenolic compounds, exhibited the activity of all studied enzymes and was the most effective in inhibiting microorganisms’ growth. For the further application of ASE, their incorporation into a biocompatible, non-toxic and mechanically suitable carrier, which enables controlled and sustained release of biologically active compounds, is important. Nanocellulose (NC) with its properties represents great potential, therefore the synthesis of NC materials and its hybrids with antibacterial properties is presented in the continuation of the doctoral dissertation. By optimizing the biosynthesis process from bacteria of the genus Komagataeibacter, bacterial nanocellulose (BNC) in the form of membranes and beads was prepared and their morphology and chemical composition were studied. The selection of the bacterial strain and the cultivation conditions were found to have a significant effect on the productivity, shape, properties and quality of BNC. K. xylinus provided rapid (3 days) and high productivity (up to 518.4 g/L) of crystalline (80.56%) BNC in the form of membranes and beads. Furter, the preparation of functionalized nanocellulose hybrids with ASE for the antibacterial applications and possible use as dressings in wound healing was carried out. ASE were incorporated into two different types of NC; BNC and cellulose nanofibrils (CNF). Morphology and chemical composition of obtained hybrids were studied, as well as a comprehensive insight into the release of ASE from NC carriers and their antibacterial effectiveness against Escherichia coli and Staphylococcus aureus, bacteria associated with skin diseases and AMR. Determination of hydrodynamic size, zeta potential and polydispersity index of ASE enabled additional explanation of possible mechanisms of antibacterial activity. BNC, enriched with ASE, showed excellent bacteriostatic and bactericidal activity, with the ability to adsorb high concentrations of ASE (up to 72.89 mg per bead and up to 46.61 mg per 1 cm2 of membrane). BNC/ASE biohybrids represent a synergistic system in which BNC provides a suitable desorption kinetic profile to enable the release of antibacterial compounds of ASE, while the high degree of swelling and water retention property have demonstrated the biohybrid's suitability for various applications related to skin regenerative medicine and wound healing. CNF, enriched with ASE (up to 14.2 mg per 1 cm2 film), also exhibited remarkable antibacterial properties (up to 100% reduction with log R up to 5.64), comparable to CNF films, enriched with the antibiotic Clindamycin (up to 100 % reduction with log R up to 6.50). The study of ASE release kinetics showed the responsiveness of CNF films to different pH environments (pH 7.4 and 5.5), which shows additional potential of CNF/ASE biohybrids and their possible positive effect in wound healing.
Secondary keywords: avocado;extraction;nanocellulose;antimicrobial activity;drug delivery;5-hidroksimetilfurfural;Disertacije;Katalitično hidrogeniranje;
Type (COBISS): Doctoral dissertation
Thesis comment: Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages: 1 spletni vir (1 datoteka PDF (XII, 118 str.))
ID: 23664928