Browsing by Author "Boyadzhieva, Stanislava"
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- Assessment of gnaphalium viscosum (Kunth) valorization prospects: sustainable recovery of antioxidants by different techniquesPublication . Boyadzhieva, Stanislava; Coelho, Jose; Errico, Massimiliano; Reynel-Avilla, H. Elizabeth; Yankov, Dragomir S.; Bonilla-Petriciolet, A.; Stateva, RoumianaThis work investigates the prospects for exploitation of Gnaphalium viscosum (Kunth) abundant but with limited applications till present biomass. The feasibility of traditional techniques (two-phase solvent, and the benchmark Soxhlet extraction) and supercritical extraction without/with a cosolvent at T = 40–60 ◦C and p = 30–50 MPa was examined to explore the possibility of recovering phytochemicals from G. viscosum leaves, flowers and stems. The efficiency of the techniques was assessed and compared based on yield, influence of solvents used, total phenolic content and antioxidant activity of the extracts. Phenolics of different complexities were identified and quantified by applying LC (LC–MS/MS, and LC–HRAM), while the fatty acid profile was determined by GC– FID. The results of this extensive study demonstrated the huge valorization potential and prospects of G. viscosum, since highly potent antioxidants such as kaempferol-3-O-β-d-glucoside (astragalin), and chlorogenic acid were ascertained in considerable amounts. Furthermore, for the first time, the presence of leontopodic acid, a greatly substituted derivative of glucaric acid, was detected in the species.
- Microwave-assisted extraction of phenolic compounds from spent coffee grounds. Process optimization applying design of experimentsPublication . Coelho, Jose; Robalo, Maria Paula; Boyadzhieva, Stanislava; Stateva, RoumianaIn this study, sustainable technology microwave-assisted extraction (MAE) in association with green solvents was applied to recover phenolic compounds from spent coffee grounds (SCGs). A design of experiments (DOE) was used for process optimization. Initially, a 2(4-1) two level Fractional Factorial Design was used and ratios "solvent to solute" and "ethanol to water" were identified as the significant experimental factors. Consequently, Central Composite Design (CCD) was applied to analyze the effects of the significant variables on the response yield, total polyphenols content (TPC), and antioxidant activity (AA) by the DPPH assay method, and quadratic surfaces to optimize those responses were generated. The values of the significant factors of 16.7 (solvent/solute) and 68.9% (ethanol/water) were optimized simultaneously the yield (%) at 6.98 +/- 0.27, TPC (mg GAE/g) at 117.7 +/- 6.1, and AA (mu mol TE/g) at 143.8 +/- 8.6 and were in excellent agreement with those predicted from the CCD model. The variations of the compositions of the lipids, caffeine, pentacyclic diterpenes, and FAME as a function of the dominant factor % ethanol in the solvent mixture were analyzed by applying NMR and GC-FID, and the results obtained confirmed their determinative significance.
- Supercritical CO2 extraction of spent coffee grounds. Influence of co-solvents and characterization of the extractsPublication . Coelho, Jose; Filipe, Rui; Robalo, M. Paula; Boyadzhieva, Stanislava; Cholakov, Georgi; Stateva, RoumianaSpent coffee grounds (SCGs) were extracted with supercritical CO2 at temperatures of 313 K and 333 K, pressures up to 50.0 MPa and different scCO(2) flow rates. The addition of co-solvents isopropanol, ethanol and ethyl lactate decreased the time to achieve the maximum oil yield, to half of that with pure CO2. Analysis of the extracted oils by NMR, showed that caffeine content was (0.56-3.96) % and DUFA and MUFA contents changed within (39.8-42.0) % and (12.9-15.8) %, respectively. The analyses of fatty acids performed by GC-FID revealed the composition of the oils being 76 % of the total constituted by palmitic and linoleic esters. The DPPH antioxidant capacity was improved up to 12.5 times with co-solvents. The kinetics of oil extraction from SCGs with pure scCO(2) was modeled successfully by combining for the first time representation of the oil mixture by a single virtual molecule with group contribution methods.