Insight into the Storage-Related Oxidative/Hydrolytic Degradation of Olive Oil Secoiridoids by Liquid Chromatography and High-Resolution Fourier Transform Mass Spectrometry

Abstract

The study of negative effects potentially exerted by the exposure to oxygen and/or light and, thus, also by the type of container on the quality of extra virgin olive oil (EVOO) during its prolonged storage requires an appropriate choice of analytical methods and components to be monitored. Here, reverse-phase liquid chromatography coupled to high-resolution/accuracy Fourier transform mass spectrometry with electrospray ionization was exploited to study oxidative/hydrolytic degradation processes occurring on the important bioactive components of EVOO known as secoiridoids, i.e., oleuropein and ligstroside aglycones, oleacin, and oleocanthal, during storage up to 6 months under controlled conditions. Specifically, isomeric oxidative byproducts resulting from the transformation of a carbonylic group of the original secoiridoids into a carboxylic group and compounds resulting from hydrolysis of the ester linkage of secoiridoids, i.e., elenolic and decarboxymethyl elenolic acids and tyrosol and 3-hydroxytyrosol, were monitored, along with their precursors. Data obtained from EVOO storage at room temperature in glass bottles with/without exposure to light and/or oxygen indicated that, although it was more relevant if a periodical exposure to oxygen was performed, a non-negligible oxidative degradation occurred on secoiridoids also when nitrogen was used to saturate the container headspace. In a parallel experiment, the effects of storage of the same EVOO (250 mL) for up to 6 months in containers manufactured with different materials/shapes were considered. In particular, a square dark glass bottle, a stainless-steel can, and a ceramic jar, typically used for EVOO commercialization, and a clear polyethylene terephthalate bottle, purposely chosen to prompt secoiridoid degradation through exposure to light and oxygen, were compared. Dark glass was found to provide the best combined protection of major secoiridoids from oxidative and hydrolytic degradation, yet the lowest levels of oxidized byproducts were observed when the stainless-steel can was used.

Exploring the Isomeric Precursors of Olive Oil Major Secoiridoids: An Insight into Olive Leaves and Drupes by Liquid-Chromatography and Fourier-Transform Tandem Mass Spectrometry

“…Consequently, isoforms with a C 8 =C 10 bond should be present in olive oil also for oleacin and oleocanthal. This hypothesis has been recently confirmed in our laboratory using the same analytical approach described in the present paper, and, notably, open-structure isoforms with a C 8 =C 10 bond have been found to prevail in the chromatographic profiles obtained for the two secoiridoids [36].…”

“…Antioxidant properties are usually recognized for these compounds and ascribed to the presence of the phenolic OH group(s). On the other hand, as recently shown in our paper on secoiridoid alterations occurring upon prolonged storage of olive oil, their C=O groups are involved in oxidation to COOH groups, especially when open-structure isoforms are considered [ 36 ]. Such isoforms could then contribute significantly to the beneficial antioxidant properties of olive oil.…”

Bioactive Compounds in Waste By-Products from Olive Oil Production: Applications and Structural Characterization by Mass Spectrometry Techniques

“…As recently evidenced for olive oil secoiridoids, whose profile is affected by various parameters, including olive cultivar and geographical origin [156], ripening stage at the harvesting time, agronomic and technological practices [157,158], and whose integrity was influenced by storage conditions [158], the distribution and integrity of phenolic compounds contained in OP and OOMW is expected to be affected as well. These differences are manifest when a comparison in quantitative terms is attempted (see Table 3).…”

Evolution of Extra Virgin Olive Oil Quality under Different Storage Conditions

“…It was demonstrated that the degradation rate of phenolic compounds during oil aging is strongly related to their initial concentration [13]. Some of the simple phenols, such as tyrosol and hydroxytyrosol, increase over time, likely owing to hydrolytic processes of secoiridoid derivatives representing their linked forms [14]. The percentage of hydrolysis typically increases in aged EVOO; therefore, the EVOO quality should be correlated to lower and not to higher values of tyrosol and hydroxytyrosol [15].…”