Studies on the Detection of Oleuropein from Extra Virgin Olive Oils Using Enzymatic Biosensors

Abstract

Oleuropein (OLEU) is an important indicator of the quality and authenticity of extra virgin olive oils (EVOO). Electrochemical sensors and biosensors for the detection of oleuropein can be used to test the adulteration of extra virgin olive oils. The present study aimed at the qualitative and quantitative determination of oleuropein in commercial EVOO samples by applying electrochemical techniques, cyclic voltammetry (CV) and square wave voltammetry (SWV). The sensing devices used were two newly constructed enzyme biosensors, supported on single-layer carbon-nanotube-modified carbon screen-printed electrode (SPE/SWCNT) on whose surface tyrosinase (SPE/SWCNT/Tyr) and laccase (SPE/SWCNT/Lac) were immobilized, respectively. The active surfaces of the two biosensors were analyzed and characterized by different methods, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR) and the results confirmed the efficient immobilization of the enzymes. SPE/SWCNT/Tyr was characterized by a low detection limit (LOD = 9.53 × 10−8 M) and a very good sensitivity (0.0718 μA·μM−1·cm−2) over a wide linearity range from 0.49 to 11.22 μM. The process occurring at the biosensor surface corresponds to kinetics (h = 0.90), and tyrosinase showed a high affinity towards OLEU. The tyrosinase-based biosensor was shown to have superior sensitive properties to the laccase-based one. Quantitative determination of OLEU in EVOOs was performed using SPE/SWCNT/Tyr and the results confirmed the presence of the compound in close amounts in the EVOOs analysed, proving that they have very good sensory properties.

Stability of target polyphenols of leaf-added virgin olive oil under different storage conditions over time

“…The storage condition/duration is among the major factors affecting the content of oleuropein which can potentially decompose in the course of the following reactions: (i) oxidation reaction 20,21 typically associated with the activities of oxidoreductase enzymes including polyphenoloxidase (PPO) that apparently have the ability to oxidize oleuropein to secondary products such as oleuropein quinone (non-bitter product) 20,21 (ii) cleavage of ester bonds 20,21 by the actions of enzymes such as esterase, that enables the formation of oleuropein derivatives including hydroxytyrosol, and (iii) de-glycosylation 20 that generates oleuropein aglycone (a potential substrate for hydroxytyrosol formation) and glucose.…”

Formation and Investigation of Physicochemical and Microbiological Properties of Biocomposite Films Containing Turmeric Extract Nano/Microcapsules

“…Stretching vibrations of the methylene (–CH 2 –) and methyl (–CH 3 ) groups can be observed at the frequencies of 2930 and 2850 cm −1 , respectively. The large peak around 1740 cm −1 is due to the stretching vibration of the C=O double bond of the oil, which overlaps with the peak from curcumin [ 38 , 39 , 40 ].…”

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

“…The biochemical degradation of oleuropein is typically associated with the exertion of the following catalyzing enzymes: (i) polyphenol-oxidase through an oxidation reaction, giving rise to the formation of secondary products; (ii) esterase through a hydrolytic reaction (as indicated earlier), giving rise to the formation of simple phenols, such as hydroxytyrosol; and (iii) b-glucosidase through de-glycosylation, giving rise to the formation of oleuropein aglycone and glucose. 21,22 In this regard, heat is among the primary factors affecting oleuropein bioconversion which can be desirable or undesirable. Given this, the rate of temperature/duration is of importance, as seen in this study where overheating resulted in substantial drops in oleuropein content.…”