Insights into the Analysis of Phenolic Secoiridoids in Extra Virgin Olive Oil

Abstract

Extra virgin olive oils (EVOOs) containing more than 5 mg/20 g tyrosol, hydroxytyrosol, and their secoiridoids can be recognized by health claims related to the protection of blood lipids from oxidative stress. Therefore, a reliable, accurate, and standardized analytical procedure is needed to determine these markers of EVOO quality. In order to overcome the limitations of current methods, a detailed investigation of sample preparation and chromatographic conditions was performed by UHPLC-UV-HRMS. The use of a C18 fused-core column and nonacidified gradient elution provided single, sharp peaks for oleocanthal and oleacein, allowing their reliable quantitation in UV profiles. Positive- and negative-UHPLC-HRMS/MS characterization of methanolic extracts revealed the presence of dimethyl acetal, methyl hemiacetal, and monohydrate derivatives of all secoiridoids. These artifacts were formed in aqueous methanol, which is usually employed to extract and analyze EVOO phenols, making the HPLC profiles more complex and the measurements less accurate and reproducible. Acetonitrile proved to be a suitable solvent to avoid the formation of secoiridoid dimethyl acetals and methyl hemiacetals and to efficiently extract EVOO bioactive phenols. Finally, the phenolic contents of Italian EVOO samples were determined by UHPLC-UV analysis of acetonitrile extracts before (direct method) and after acid hydrolysis (indirect method). The results indicated that the use of tyrosol and hydroxytyrosol as reference standards allowed more accurate quantitative data to be obtained. Direct and indirect methods provided comparable levels of EVOO phenols, highlighting the usefulness of acid hydrolysis in routine analyses. The improved procedure defines the most reliable conditions to provide an analytical method with suitable accuracy and repeatability in the analysis of healthy and functional EVOO phenols.

By-Products from Winemaking and Olive Mill Value Chains for the Enrichment of Refined Olive Oil: Technological Challenges and Nutraceutical Features

“…Among flavonoids, luteolin (compound 17 ) was detected. These results are in agreement with the chemical profile of olive oil reported by previous studies [ 36 , 48 ].…”

“…The obtained chromatographic profiles operating in negative ion mode are showed in Figure 2 , while detected compounds are described in Table S1 . Compounds were tentatively identified according to MS and literature data [ 37 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ]. Several substances were not completely identified but based on the MS fragmentation patterns their structure was correlated to some principal skeletons.…”

Absorption and Intestinal Metabolic Profile of Oleocanthal in Rats

“…The secoiridoids are the most abundant and complex family of phenolic compounds in extra virgin olive oil (EVOO). The main secoiridoids compounds identified in EVOO are the monoaldehydic forms of oleuropein (3,4-DHPEA-EA) and ligstroside aglycones (p-HPEA-EA) and the dialdehydic forms of their decarboxymethylated derivatives, oleacein (3,4-DHPEA-EDA) and oleocanthal (p-HPEA-EDA) [1]. Since its identification in 1993 [2], oleocanthal (OLC) has been targeted by numerous in vitro and in vivo studies aiming to understand the health effects of EVOO consumption [3].…”

Probing Downstream Olive Biophenol Secoiridoids

“…Olives and olive oil have been found to naturally protect against stroke, degenerative and cardiovascular diseases as well as cancer and obesity [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. Extra virgin olive oil is one of the essential sources of monoenoic fatty acids and biophenol (BP)-based bioactives [ 10 , 11 ]. The major BPs from olive products include phenolic acids and alcohols as well as secoiridoids, while the minor contents are flavonoids and lignans [ 12 ].…”

“…Olive leaves contain a higher concentration of BPs with secos of 1450 mg/100 FW (fresh weight) compared to the olive fruit and oil, which have 110 mg/100 g and 23 mg/100 mL, respectively [ 9 ]. Oleuropein and ligstroside aglycones, oleacein, oleocanthal, hydroxytyrosil-elenolate, tyrosil-elenolate, oleoside-11-methyl ester, elenoic acid, hydroxytyrosol, and tyrosol are downstream pathway bioactives from oleuropein and ligstroside precursors [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Oleuropein is the principal BPseco in green olive fruits, leaves, and table olives, whereas olive oil is rich in its downstream metabolites [ 16 , 17 , 18 ].…”