Browsing by Author "Stoylov B."

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    Mass transfer intensification in bioactive compounds recovery by alternative extraction methods: Effects of solvent
    (2019-02-01) Atanasov S.; Stoylov B.; Saykova I.; Tchaoushev S.
    Recently, the exploration of new alternatives to common organic solvents in combination with non-conventional energy sources is a subject of intense research and development as tools for green extraction of plant-derived natural products. This paper deals with the use of low frequency ultrasound (100 W, 32 kHz) and pulsed electrical fields (0.86 kV cm-1, 13 Hz) to raise the efficiency of the extraction of selected plant species rich in valuable phenolic compounds. Four types of natural deep eutectic solvents were applied for the ultrasound-assisted extraction of silymarin from milk thistle among which a choline-chloride-based mixture with glycerol was proved to be the most promising one. Additionally, the usage of high ultrasound power significantly increased the concentration of sylimarin as compared to traditional ethanol extraction, generating rapidly for 10 min considerable temperature rise as a side effect under non-cooling conditions. The application of PEF as a pre-treatment for 0.8 s to the extraction allowed reducing the ethanol percentage in the ethanol/water mixtures giving comparable phenolic yields, without any, or very little, increase in temperature. As such, optimized power intensity in conjunction with appropriate solvent system provides a potential to improve the release of thermally unstable bioactive compounds under mild processing conditions.
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    PULSED ELECTRIC FIELD EXTRACTION OF VALUABLE COMPOUNDS FROM GRAPE SEEDS
    (2022-01-01) Saykova I.; Iatcheva I.; Stoylov B.
    The seeds of grape are known as a valuable source of phenolic compounds, which may act as radical scavengers by converting free radicals into less reactive species. Maintaining their quality during processing is an important feature since most of them are thermo-sensitive compounds susceptible to oxidation and degradation. In this paper, pulsed electric field (PEF) under moderate field strength (0.86 kV cm-1, 900 short pulses of 100 μs) was applied as a pretreatment to facilitate the phenolic extraction. The impact of PEF was discussed compared with conventional extraction with 50 % aqueous ethanol from whole intact seeds and the residue from seed oil cold-pressing. The kinetic behavior of the antioxidant activity of extracts was evaluated using DPPH assays to assess the correlation of total phenolic content and antioxidant activity. Compared to the cold pressing pretreatment or conventional extraction at 60°C, the PEF was not competitive in terms of recovery rate but represented a suitable method to produce highpurity extracts with beneficial antioxidant properties.