**7. Conclusions**

Plant antioxidant action for the benefit of human health/well-being may occur by a variety of mechanisms. As in the case of therapeutic drugs, industry has to address the mode of action of "antioxidants". Direct mechanisms include quick REDOX reactions occurring locally but, also, the action of a given compound that after blood-mediated distribution into a target tissue participates in an enzyme-catalyzed REDOX reaction.

Indirect mechanisms, more di fficult to measure but with significant potential to help in development of the industry of plant supplements and nutraceuticals, include actions such as boosting innate mechanisms of detoxification. Hormetic processes, also indirect, should be considered since plant derivatives may provide pro-oxidants able to upregulate the expression of enzymes of innate detox pathways or, alternatively, regulators of the expression of vitagenes (as defined in [48]).

Finally, it is likely that molecules present in chloroplast and mitochondria of plant cells (and therefore in plant extracts) may reach the mitochondria of mammalian cells to make electron transport and oxidative phosphorylation more e fficient. One of the causes of oxidative stress is malfunctioning of mitochondria due to a disease and/or to aging.

Nutraceutical industry, focusing more on mechanisms, could select the best candidates from the myriad of plant-derived molecules that can be divided as more beneficious or as detrimental (or less beneficious). Furthermore, the industry must consider that, often, in vitro measured antioxidant power does not correlate with antioxidant action at the physiological level.

**Author Contributions:** R.F., G.N. and E.M.-P. scanned the literature, retrieved and processed papers referenced in the review. R.F. compiled all the information and wrote the first version of the manuscript. G.N. and E.M.-P. critically read the manuscript, prepared a second version and the tables/figures in all versions of the paper. All authors edited the manuscript and revised the final submitted version.

**Funding:** This research received no external funding.

**Acknowledgments:** In Memoriam: Adela Mazo, a brilliant chemistry student, a master of REDOX chemistry and stunning as colleague. In Memoriam: Jesús (Suso) Pintor who produced stunning papers and was as good as scientist as a person (we miss you Suso). We acknowledge the inspiring work of Vince Gilligan and his team, especially for this quote: "I simply respect Chemistry. Chemistry must be respected"—Walter White. Anything good or bad occurring in life has a common factor: Chemistry.

**Conflicts of Interest:** The authors declare no conflict of interest.
