VALORIZATION OF GRAPE WINE POMACE USING PULSED ELECTRIC FIELDS (PEF) AND SUPERCRITICAL CO₂ (SC CO₂) EXTRACTION

Abstract

Wine grape pomace quantitatively and qualitatively represents the most important fraction of wine waste. Namely, this by-product makes ~ 20% of the total mass of vinified grapes, and it is characterized with high concentrations of polyphenolic antioxidants, as well as grape seed oil. Hence, valorization of wine pomace, as an alternative to traditionally employed disposal, has drown considerable interest in recent years. Earlier studies were mostly focused on the extraction of phenolics, while mechanisms enhancing the extraction of lipid fraction from grape pomace, as well as their impact on the grape seed oil quality are far less investigated. In addition, opposed to conventional solvent extraction methods, new trends lead to the employment of eco-friendly extraction technologies as supercritical CO₂ (SC CO₂) extraction. The aim of this research was to study impact of low and high intensity pulsed electric fields (PEF) pretreatments prior to SC CO₂ extraction of grape seed oil, from Graševina grape pomace, on the oil yield and chemical composition. Results showed that PEF assisted SC CO₂ extracted more than 95% of pomace lipids and contributed to significantly higher concentrations of both lipophilic (sterols and tocochromanols) and hydrophilic antioxidants (polyphenolic compounds) in grape seed oil. These concentrations were up to 10% higher for total sterols, but even more than 50% higher for total tocochromanols and total individual polyphenols, respectively. PEF pretreated samples showed significantly higher concentrations of stigmasterol, β-sitosterol, Δ5-avenasterol, Δ5,24-stigmastadienol and Δ7-avenasterol. Moreover, significantly higher concentrations of all analyzed tocochromanols were also found in these samples, primarily of β-tocopherol, plastochromanol-8 and α-tocotrienol that showed more than two times higher values. In addition, PEF pretreatments significantly contributed to the extraction of all individual polyphenolic compounds, while more than two times higher concentrations were found for gallic, p-coumaric and ferulic acids. Moreover, PEF assisted SC CO₂ extraction showed favorable effect on the extraction of the most abundant fatty acid, linoleic acid. Finally, the highest concentrations of both lipophilic and hydrophilic compounds were extracted by PEF pretreatment of higher intensity.