engleski

Optimization of microwave-assisted extraction of polyphenols from olive pomace

Olive pomace (OP) is a solid residue that is lagging behind in the production of olive oil. It contains various biologically active polyphenols (PP), primarily hydroxytyrosol (HTS), oleuropein (OLE), and tyrosol (TS) [1]. The potential of OP as the starting raw material for obtaining PP is not even close to fully utilized. The main reason is unavailability of adequate methods for the isolation of PP which leads to poor quality of obtained extracts being unsuitable for futher testing and processing. The aim of this study was to develop and optimize environmentally and economically acceptable ("green") microwave- assisted extraction (MAE) for obtaining high- quality extracts in terms of total phenolic content (TPC) and the content of hydroxytyrosol derivatives (the sum of tyrosol, hydroxytyrosol and oleuropein) representing the main bioactive fraction of OP. Fast and simple MAE has been proposed as an alternative to conventional (solid-liquid) extraction in water-bath and ultrasound-assisted extraction (UAE). For MAE optimization Full Factorial (FF) design was used for studying the effects of three independent factors: 1) extraction solvent (20─96% ethanol) ; 2) microwave power (400─700 W) ; and 3) time of extraction (─10 min). TPC was determined using Folin- Ciocalteu method [2]. HPLC coupled with fluorescent detector was used for the separation and quantification of analytes, hydroxytyrosol derivatives. Our results indicate that all analysed factors (microwave power, extraction time and concentration of ethanol) and their interactions had significant influence on TPC and the content of hydroxytyrosol derivatives. The highest yields of both, PP and hydroxytyrosol derivatives were obtained with the microwave power of 700 W, extraction time of 10 minutes, and 20% ethanol. In comparison to yields obtained under optimum conditions of UAE and conventional extraction [3], MAE was found to be superior method, requiring shorter extraction time and showing better efficiency.

microwave-assisted extraction, olive pomace, hydroxytyrosol, tyrosol, oleuropein

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