**4. Conclusions**

A green and simple method, using food grade reagents, was set up as an on-site, environment- and operator-friendly tool for screening of olive oils according to the content of total (i.e., free and linked) OHTyr and Tyr. The reagents (glucose, lactic acid, and water) and the equipment (a spectrophotometer) required make this method affordable and feasible in contexts other than analytical labs. The limits of detection and quantitation (3.9 and 11.8 mg kg−1) and the repeatability (CV% ≤ 5%) can be considered satisfactory for screening purposes. The results obtained, although leading to a slight overestimation, fit with those obtained by the reference HPLC method, and showed good predictive capacity. The NADES-UV method could be a suitable complement to more complex methods (involving extraction, acid hydrolysis, and HPLC analysis) that seem to be the best approach to address the requirements of the EFSA health claim. The availability of a complete analytical platform comprising both on-site screening methods and accurate laboratory determination could support the value chain operators in EVOO differentiation and segmentation, as well as consumers in gaining increasing awareness.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/2304-815 8/10/3/677/s1. Table S1: Contents of OHTyr an Tyr in the EVOO samples set, determined by the reference method before and after acid hydrolysis.

**Author Contributions:** Conceptualization, V.M.P. and F.C.; methodology, V.M.P., F.L. and N.M.; formal analysis, V.M.P. and F.L.; investigation, S.F., L.C., M.B., P.R.; resources, F.C., P.C. and N.M.; writing—original draft preparation, V.M.P. and F.L.; writing—review and editing, M.B., L.C., P.C. and F.C.; visualization, V.M.P.; supervision, F.C. and N.M.; project administration, V.M.P. and F.L.; funding acquisition, V.M.P. and F.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by AGER 2 Project (grant no. 2016-0105) and by Regione Puglia (POR Puglia FESR-FSE 2014–2020—Innonetwork call—"Multifunctional microsystems for the monitoring of olive oils oxidation"—project code XMPYXR1).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

#### **References**

