Extractability of oleuropein, hydroxytyrosol, tyrosol, verbascoside and flavonoid-derivatives from olive leaves using ohmic heating (a green process for value addition)

Abstract

This figure highlights the effectiveness of ohmic heating (considering extraction temperature and solvent ratio) compared to conventional heating in the recovery of representative polar phenols of olive leaves.

Effect of storage, temperature, and pH on the preservation of the oleuropein content of olive leaf extracts

“…As a side note, in our previous study, this particular extraction method (ohmic at 75 °C) comparably favored a higher antiradical capacity of the extracts. 11 This in part could be attributed to the presence and bioactivity of oleuropein, which probably acted as a pronounced radical scavenger proportion-dependently.…”

“…Olive mill leaves from the same cultivar (Picual) and growing area as those applied in our earlier experiment 11 were kindly supplied by “Center for Advanced Studies in Energy and Environment”, University of Jaén, Campus of Las Lagunillas, Jaén, Spain. Upon arrival, they were cleaned, dried, and ground using the same methods as practiced previously.…”

“…The extraction processing design in this study was identical to that practiced in our previous study. 11 Briefly, olive leaves were initially cleaned, washed, and dried at 37 °C for 48 h. The dried leaves were then ground and size reduced to 0.3 mm. The dry ground olive leaves (solid : solvent ratio of 1 : 10) were then subjected separately to each selected extraction protocol (Table 1) using the following techniques: (i) ohmic heating (OH), (ii) conventional heating (Conven), and (iii) Control (solvent agitation without heating, 25 ± 5 °C).…”

“…The total phenolic content (TPC) was determined using the method of Singleton et al 13 with some modifications as previously noted. 11 An aliquot of 100 μL extract was first diluted with 6 mL distilled water. The solution was then reacted with 500 μL of Folin–Ciocalteau reagent and vigorously mixed.…”

“…Given the importance of the factor of preservation, the present study extended the previous research to assess the stability of olive leaf extracts obtained by ohmic heating (that showed significant effectiveness in the extraction of polyphenols)‎ 11,12 under the following environmental conditions: (i) varying storage temperatures over different time points, (ii) thermal conditions over different heating time points, and (iii) differing pH solutions. Beyond assessing the changes in the total phenolic content (TPC), special attention was placed on the variations of oleuropein under the selected conditions.…”