Determination of polyphenolic compounds and antioxidant activity of extracts from olive leaves by means of high voltage electrical discharges

Listovi masline smatraju se jeftinom sirovinom koja može poslužiti kao izvor visokovrijednih bioaktivnih spojeva, s potencijalnom primjenom u prehrambenoj industriji. Svrha ovog istraživanja bila je utvrditi učinak visokonaponskog električnog pražnjenja (HVED), kao zelene metode ekstrakcije, na efikasnost ekstrakcije fenolnih spojeva iz lista masline te usporediti HVED metodu s konvencionalnom metodom ekstrakcije. HVED tretman provodio se kroz različito vrijeme (3 i 9 min), u različitim zelenim otapalima (voda, etanol), radnim plinovima (dušik, argon) i pri različitim naponima (15, 20, 25 kV). Fenolni spojevi određeni su pomoću tekućinske kromatografije ultra visoke djelotvornosti s detekcijom masene spektrometrije (UPLC-MS/MS), dok su udio ukupnih fenola i antioksidacijska aktivnost određeni spektrofotometrijski. Prikazani su i rezultati blisko-infracrvene (NIR) spektroskopije i veličine čestica ekstrakta lista masline. Najveći prinos fenolnih spojeva uočen je u uzorku tretiranom argonom, 9 min, 20 kV i u 50 %-tnoj otopini etanola. Antioksidacijska aktivnost određena FRAP metodom bila je veća u HVED tretiranim uzorcima, dok DPPH i ORAC metoda nisu pokazale značajnu razliku nakon HVED tretmana. Razvijeni su i regresijski modeli za predviđanje sadržaja ukupnih fenola i antioksidacijske aktivnosti sličnih uzoraka na temelju analitičkih podataka i NIR spektroskopije.Olive leaves are considered as a cheap raw material which can be used as a source of valuable bioactive compounds, with potential application in food industry. The aim of this study was to evaluate high voltage electrical discharges (HVED) as a green technology, in order to establish the effectiveness phenolic extraction from olive leaves and compare HVED method with conventional extraction. HVED processing parameters were: treatment time (3 and 9 min), different green solvents (water, ethanol), working gases (nitrogen, argon) and voltages (15, 20, 25 kV). Individual phenolic compounds were characterized by ultra-performance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS), while the content of total phenolics and antioxidant activity were determined spectrofotometrically. Results for Near infrared (NIR) spectroscopy and particle size of olive leaves extract were also reported. The highest yield of phenolic compounds was obtained for the sample treated with argon, 9 min, 20 kV and 50 % solution of ethanol. Antioxidant activity determined by FRAP method was higher in HVED treated samples, while DPPH and ORAC method showed no significant difference upon the HVED treatment. Regression models were developed for prediction total phenolic content and antioxidant activity of similar samples based on analytical data and NIR spectroscopy