Potential of LC Coupled to Fluorescence Detection in Food Metabolomics: Determination of Phenolic Compounds in Virgin Olive Oil

Extraction Systems and Analytical Techniques for Food Phenolic Compounds: A Review

Phenolic compounds are highly valuable food components due to their potential utilisation as natural bioactive and antioxidant molecules for the food, cosmetic, chemical, and pharmaceutical industries. For this purpose, the development and optimisation of efficient extraction methods is crucial to obtain phenolic-rich extracts and, for some applications, free of interfering compounds. It should be accompanied with robust analytical tools that enable the standardisation of phenolic-rich extracts for industrial applications. New methodologies based on both novel extraction and/or analysis are also implemented to characterise and elucidate novel chemical structures and to face safety, pharmacology, and toxicity issues related to phenolic compounds at the molecular level. Moreover, in combination with multivariate analysis, the extraction and analysis of phenolic compounds offer tools for plant chemotyping, food traceability and marker selection in omics studies. Therefore, this study reviews extraction techniques applied to recover phenolic compounds from foods and agri-food by-products, including liquid-liquid extraction, solid-liquid extraction assisted by intensification technologies, solid-phase extraction, and combined methods. It also provides an overview of the characterisation techniques, including UV-Vis, infra-red, nuclear magnetic resonance, mass spectrometry and others used in minor applications such as Raman spectroscopy and ion mobility spectrometry, coupled or not to chromatography. Overall, a wide range of methodologies are now available, which can be applied individually and combined to provide complementary results in the roadmap around the study of phenolic compounds.

A Critical Appraisal of the Separation Protocols Proposed for the Implementation of the Health Claim on “Olive Oil Polyphenols” (EC Regulation 432/2012)

The analysis of the secoiridoid type of phenolic compounds present in virgin olive oil has become a challenging area of research since the first evidence of their presence in the polar fraction of the oil. Separation techniques, mainly liquid chromatographic ones, prevailed over the years of application toward elucidation of their structure, content determination and collection of evidence on cultivar, origin, processing and storage conditions dependence. One of the latest challenges in their analysis was related to the need to address the requirement set by EC Regulation 432/2012 for the implementation of the health claim on ‘olive oil polyphenols’. The present work considers in a chronological order the original articles, viewpoints, review articles and other published efforts that appeared in the literature after the issuing of the relevant EFSA scientific opinion in 2011. The EFSA health claim created a lot of expectations among producers of virgin olive oil and boosted research for the development of a ‘fit for the purpose’ analytical protocol. Emphasis is given to the dedicated separation protocols that have been developed in the last 10 years and to the progress in their validation in comparison to the features of the method that were recently adopted by the International Olive Council.

Metabolomics and metabolites in ischemic stroke

Stroke is a major reason for disability and the second highest cause of death in the world. When a patient is admitted to a hospital, it is necessary to identify the type of stroke, and the likelihood for development of a recurrent stroke, vascular dementia, and depression. These factors could be determined using different biomarkers. Metabolomics is a very promising strategy for identification of biomarkers. The advantage of metabolomics, in contrast to other analytical techniques, resides in providing low molecular weight metabolite profiles, rather than individual molecule profiles. Technically, this approach is based on mass spectrometry and nuclear magnetic resonance. Furthermore, variations in metabolite concentrations during brain ischemia could alter the principal neuronal functions. Different markers associated with ischemic stroke in the brain have been identified including those contributing to risk, acute onset, and severity of this pathology. In the brain, experimental studies using the ischemia/reperfusion model (IRI) have shown an impaired energy and amino acid metabolism and confirmed their principal roles. Literature data provide a good basis for identifying markers of ischemic stroke and hemorrhagic stroke and understanding metabolic mechanisms of these diseases. This opens an avenue for the successful use of identified markers along with metabolomics technologies to develop fast and reliable diagnostic tools for ischemic and hemorrhagic stroke.

Assessment of paprika geographical origin fraud by high-performance liquid chromatography with fluorescence detection (HPLC-FLD) fingerprinting

Paprika production under the protected designation of origin (PDO) standardized procedures leads to more quality products. However, it is also related to higher retail prices, making them susceptible to adulteration with low-quality paprika or its agricultural origin's mislabeling. Therefore, in this study, high-performance liquid chromatography with fluorescence detection (HPLC-FLD) fingerprints, strongly related to phenolic acid and polyphenolic compounds, were proposed as chemical markers to assess the classification of paprika from five European regions (three Spanish PDO, Hungary, and the Czech Republic), through a classification decision tree constructed by partial least squares regression-discriminant analysis (PLS-DA) models. After external validation, an excellent classification accuracy of 97.9% was achieved. Moreover, the chromatographic fingerprints were also proposed to detect and quantitate two different paprika geographical origin blend scenarios by partial least squares (PLS) regression. Low external validation and prediction errors -with values below 1.6 and 10.7%, respectively- were obtained.

Influence of fruit canopy position and maturity on yield determinants and chemical composition of virgin olive oil

BACKGROUND

While both maturity and light exposure are important factors determining olive fruit physiology, the relationship between maturity, canopy position and optimal harvesting time has not been well-studied. To understand the interaction of these factors, olive fruits from upper and lower layers of the canopy were harvested from September to January. Maturity, moisture and fat content of the fruit as well as the quality and minor components of the oil extracted were measured.

RESULTS

Lower light interception at the lower canopy positions resulted in differences in the fruits and oil extracted between canopy layers. Upper layer presented 60% of the overall production; fruit had one unit more of maturity index, 3% less moisture and 5% more fat content. Oil extracted from the upper layers presented higher concentration of oleuropein and ligstroside aglycone. Fruits from upper layers at maturity index of two had higher fat content and more total phenols in the oil extracted when compared with fruits from lower layer with the same maturity index.

CONCLUSIONS

Differences in oil composition between layers do not correlate with differences in the fruit maturity index; instead, fruit position is a determining factor for physiological processes related to fruit growth and oil composition. © 2019 Society of Chemical Industry.