engleski

INFLUENCE OF BIOLOGICAL PRETREATMENT OF GRAPE POMACE ON PHENOLIC COMPOUNDS EXTRACTION

Grape pomace is an inexpensive solid by-product remained after winemaking process representing the rich source of bioactive phenolic compounds. Extraction of bioactive phenolic compounds is the first step in their utilization from natural sources and is usually performed by organic solvents. This method is however only effective for simple and free phenolic compounds, while the highly polymerized phenolic compounds bonded in complexes with proteins, fibres and polysaharides are not extractible by this method. One of the possible ways to release that compounds is biological pretreatment of natural sources, e.g. agro-food industrial residues. The aim of this work was to investigate the influence of biological pretreatment of grape pomace with white-rot fungi Trametes versicolor on the enhancement of phenolic compounds (total phenolic compounds, TPC ; total extractible proanthocyanidins, TPA ; total flavonoids, TF) extraction efficiency as well as antioxidant activity (AA) of grape pomace extracts. A white- rot fungus T. versicolor was cultivated on grape pomace in solid-state conditions (SSF) during twenty days. Phenolic compounds were extracted from grape pomace before, during and after SSF by 50 % aqueous ethanol at 80 °C during two hours. Grape pomace extracts were analysed spectrophotometrically using Folin-Ciocalteu micro-method at 765 nm, method based on acid hydrolysis and formation of red colour at 540 nm, the aluminium chloride colorimetric assay at 510 nm, for TPC, TPA and TF, respectively. AA of extract were evaluated by spectrophotometric method at 515 nm against stable 2.2 diphenil-1- picrylhydrazyl radical (DPPH•). Initial concentrations of phenolic compounds and antioxidant activity were 28.47 mgGAE/gdb, 16.77 mg/gdb, 21.06 mgCE/gdb, and 0.18 ginhDPPH/gdb for TPC, TPA, TF and AA, respectively. Biological pretreatment, however, did not enhance the extractability of phenolic compounds. The results obtained after SSF were lower up to 68.2 %, 93.1 %, 82.5 % and 78.9 % for TPC, TPA, TF and AA, respectively.

Grape pomace; Phenolic compounds; Trametes versicolor.

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