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Efficient and Green Isolation of Keratin from Poultry Feathers by Subcritical Water
Mojca Škerget, Maja Čolnik, Lidija Fras Zemljič, Lidija Gradišnik, Tanja Živković Semren, Blanka Tariba Lovaković, Uroš Maver, 2023, izvirni znanstveni članek

Opis: The isolation of keratin from poultry feathers using subcritical water was studied in a batch reactor at temperatures (120–250 °C) and reaction times (5–75 min). The hydrolyzed product was characterized by FTIR and elemental analysis, while the molecular weight of the isolated product was determined by SDS-PAGE electrophoresis. To determine whether disulfide bond cleavage was followed by depolymerization of protein molecules to amino acids, the concentration of 27 amino acids in the hydrolysate was analyzed by GC/MS. The optimal operating parameters for obtaining a high molecular weight protein hydrolysate from poultry feathers were 180 °C and 60 min. The molecular weight of the protein hydrolysate obtained under optimal conditions ranged from 4.5 to 12 kDa, and the content of amino acids in the dried product was low (2.53% w/w). Elemental and FTIR analyses of unprocessed feathers and dried hydrolysate obtained under optimal conditions showed no significant differences in protein content and structure. Obtained hydrolysate is a colloidal solution with a tendency for particle agglomeration. Finally, a positive influence on skin fibroblast viability was observed for the hydrolysate obtained under optimal processing conditions for concentrations below 6.25 mg/mL, which makes the product interesting for various biomedical applications.
Ključne besede: poultry feathers, subcritical water hydrolysis, keratin, physico-chemical characterization, cytotoxicity
Objavljeno v DKUM: 28.11.2023; Ogledov: 64; Prenosov: 3
.pdf Celotno besedilo (2,78 MB)
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Kinetics study of hydrothermal degradation of PET waste into useful products
Maja Čolnik, Darja Pečar, Željko Knez, Andreja Goršek, Mojca Škerget, 2022, izvirni znanstveni članek

Opis: Kinetics of hydrothermal degradation of colorless polyethylene terephthalate (PET) waste was studied at two temperatures (300 °C and 350 °C) and reaction times from 1 to 240 min. PET waste was decomposed in subcritical water (SubCW) by hydrolysis to terephthalic acid (TPA) and ethylene glycol (EG) as the main products. This was followed by further degradation of TPA to benzoic acid by decarboxylation and degradation of EG to acetaldehyde by a dehydration reaction. Furthermore, by-products such as isophthalic acid (IPA) and 1,4-dioxane were also detected in the reaction mixture. Taking into account these most represented products, a simplified kinetic model describing the degradation of PET has been developed, considering irreversible consecutive reactions that take place as parallel in reaction mixture. The reaction rate constants (k1–k6) for the individual reactions were calculated and it was observed that all reactions follow first-order kinetics.
Ključne besede: PET waste, subcritical water, kinetics, degradation, TPA
Objavljeno v DKUM: 18.09.2023; Ogledov: 213; Prenosov: 12
.pdf Celotno besedilo (2,22 MB)
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Hydrothermal processes for conversion of lignocellulosic biomass to value-added compounds : doctoral disertation
Tanja Milovanović, 2020, doktorska disertacija

Opis: In this doctorial dissertation subcritical water processes of lignocellulosic biomass to obtain value-added compounds are studied. The doctorial dissertation is divided into four main parts. In the first and second part of dissertation, model compounds (standards of cellulose and sugars and chestnut tannins) were primarly used in order to better understand processes of real biomass material. The degradation of cellulose and different sugars was performed in batch reactor with subcritical water. The different reaction temperatures and times were used. The main phases, such as water-soluble fraction, acetone-soluble fraction and solid residue were separated and analysed. The analysis of water-soluble phase was done by HPLC equipped with UV and RI detector, while acetone-soluble phase of cellulose was analysed by GC-MS. Total sugar content was determined by the phenol-sulphuric acid colorimetric method. The properties of char, obtained using cellulose as a treated material, such as: specific surface area, pore volume and pore diameter were determined by gas adsorption method. A water-soluble phase mainly consists of sugar monomers and monomer degradation products such as 5-hydroxymethylfurfural (5-HMF), furfural, erythrose, sorbitol, 1,6-anhydroglucose, glycolaldehyde, glycerlaldehyde, 1,3-dihydroxyacetone, pyruvaldehyde, formic, levulinic, lactic, oxalic and succinic acids, while acetone-soluble phase, referred to also as bio-oil, consists of furans, phenols, carboxylic acids, aldehydes, ketones and high molecular compounds. The reaction mechanism of cellulose and sugars in subcritical water has been proposed based on the obtained results. Furthermore, the results from cellulose and sugar hydrothermal degradation were utilized in further work to determine which industrially interesting products could be obtained by hydrothermal processing of paper waste in subcritical water. The optimum conditions ( temperature and reaction time), which gave us the highest yield of base chemicals (furfural, 5-HMF, levulinic acid) were determined. Sweet chestnut (Castanea Sativa) bark contains high level of tannins and various phenolic compounds which can be utilized in pharmaceutical, cosmetic, nutritional and medical purposes. The sweet chestnut tannins extract and sweet chestnut bark were used as materials highly rich in bioactive compounds for subcritical water processes which are presented in the second part of doctorial dissertation, respectively. The spectrophotometric methods were used to determine total tannins, phenols and carbohydrates content and antioxidant activity. The identified compounds were ellagic and gallic acid, ellagitannins (vescalagin, castalagin, 1-o-galloyl castalagin, vescalin and castalin), sugars (maltose, glucose, fructose and arabinose) and sugar derivatives (5-HMF, furfural and levulinic acid). The results obtained from hydrothermal hydrolysis were compared to results from acid hydrolysis. Finally, the optimization of reaction parameters of subcritical water processes has been done aiming to obtain the product highly rich in ellagic acid. Subcritical water extraction of horse chestnut (Aesculus hippocastanum) parts such as seeds, seed shell, bark and leaves was described in the third chapter of dissertation. The detected compounds in extracts, such as escins, esculin, fraxin, phenolic compounds (chlorogenic, neochlorogenic and gallic acids) and furfurals (5-hydroxymethyfurfural, furfural, and methylfufrual) are quantified using HPLC. The last part of dissertation proposes extraction of cocoa shell using green technologies (supercritical CO2 and subcritical water extraction) and also conventional methods (Soxhlet extraction with hexane and extraction with 50 % acetone) to obtain bioactive compounds in order to compare the results. The detected compouns were methylxanthines, phenolic compounds, sugars, fatty acids.
Ključne besede: Subcritical water, biomass, biowaste, extraction, hydrothermal degradation, hydrolysis, bioactive compounds.
Objavljeno v DKUM: 16.10.2020; Ogledov: 1325; Prenosov: 150
.pdf Celotno besedilo (6,32 MB)

Subcritical water as a green medium for extraction and processing of natural materials
Matej Ravber, 2016, doktorska disertacija

Opis: In this doctoral dissertation, the application of subcritical water as a green medium for the extraction and processing of natural materials is presented. The work is divided into three main parts. In the first part, subcritical water is proposed as a solvent for the simultaneous extraction of oil- and water-soluble phase from oily seeds. The extraction parameters, such as temperature, time and material to solvent ratio that yield the highest amounts of both phases are examined. The quality of both obtained phases is examined. The characteristics of oils obtained using subcritical water is compared to that obtained using a conventional method. The second part of this work proposes subcritical water as an efficient solvent for the isolation of bioactive phenolic compounds from wood waste, that is produced by the forestry industry. Different wood fractions are firstly extracted in batch-mode and the fraction with the highest amounts of bioactive compounds is determined. Next, semi-continuous operation is applied, where the effects of different extraction parameters are studied on the extraction yield and quality of the extract. The effect of temperature and ethanol addition to the subcritical water on the content of single phenolic compounds identified in the extracts is observed. Lastly, the cost of manufacturing of such a product is estimated by evaluating the economics of different pilot- and industrial-scale processes operating at optimal conditions determined on the laboratory scale. The last part proposes the use of subcritical water as an efficient hydrolytic medium for glycoside bonded antioxidants, specifically those found in waste agro-industrial sources. Effect of temperature, treatment time, concentration and the atmosphere used for establishing the pressure in the reactor are first studied on a model glycoside compound - rutin and the optimal combination of reaction parameters are established for the batch-mode reactor. The degradation products of the model compound are identified and the concentration/time profiles of their degradation are observed. Furthermore, the reaction kinetics explaining the degradation of the rutin standard are evaluated. In the next step, the method is implemented on a real glycosides-containing extract. The extract is hydrolyzed at conditions obtained from the first step and the free aglycone is obtained at the highest yields possible. Lastly, the process is upgraded to continuous operation and the final hydrolyzed high-purity product is recovered.
Ključne besede: Subcritical water, Biowaste, Extraction, Hydrolysis, Antioxidants, Hydrothermal degradation.
Objavljeno v DKUM: 16.06.2016; Ogledov: 1633; Prenosov: 226
.pdf Celotno besedilo (3,71 MB)

Extraction of curcuminoids with subcritical water : diploma thesis
Ignacio Macicior Borregón, 2015, diplomsko delo

Ključne besede: subcritical water, extraction, curcuma
Objavljeno v DKUM: 06.11.2015; Ogledov: 1334; Prenosov: 60
.pdf Celotno besedilo (1,47 MB)

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