Phenolic Profile and Thermal Stability of Monovarietal Extra Virgin Olive Oils Based on Synchronous Fluorescence Spectroscopy.

Abstract

The olive oil production in Pakistan has recently been started with the cultivation of exotic cultivars that are successfully adapted at Barani Agriculture Research center (BARI), Chakwal, Pakistan in Potohar valley. Therefore, characterization of extra virgin olive oil (EVOO) from this agro-climatic region is mandatory in establishing its biochemical profile and thermal stability. Seventeen monovarietal EVOOs extracted from these cultivars were analysed using synchronous fluorescence spectroscopy (SFS) and subjected to heating at 115, 150 and 170°C for 15min to identify their thermal stability. SFS emission spectra differentiated EVOOs on the basis of phenolic compounds that are denatured at high temperature, further chlorophyll contents also decreased with increasing temperature. The strong emission at ca. 351nm, suggested to be vanillic acid, 391-471nm for blue green region (BGR) assigned to other phenolic compounds and two peaks at 672 and 723nm for chlorophyll became the bases for grouping through Hierarchical clustering. Most of the EVOOs were stable at 150°C but showed denatured spectra at 170°C, the only EVOO extracted from Spanish cultivar Arbequina was found to have moderate fluorescence emission from both vanillic acid and BGR that are more likely to impart oxidative stability even after heating at 170°C, also confirmed by lowest values of specific extinction co-efficient (K232 and K270). Moreover, variation in phenolic contents of Arbequina EVOO was observed with different harvesting stages and the early harvested olives produced more thermally stable oil as compared to late harvested olives. Arbequina oil grown in Pakistan can be better suited for cooking at high temperatures, moreover can be blended with other monovarietal EVOOs to enhance the nutritional benefits and thermal stability.