## 1 Introduction
### Antioxidant Activity
#### 1.1.1 Antioxidant Activity of Salvia Extracts--Chemical Models  
As for plants in general, the antioxidant potential of sag extracts has been evaluated as a first approach through in vitro methods (Table 1), including the capacity to scavenge stable free radicals such as DPPH\({}^{\bullet}\) (2.2-diphenyl-1-picrylhydraz), ABTS\({}^{\bullet}\) (2.2'-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid), hydroxyl (\({}^{\bullet}\)OH), superoxide (O\({}_{2}\)\({}^{\bullet-}\)) and nitric oxide (NO\({}^{\bullet}\)), and also by the ability to reduce metal ions from their higher to their lower oxidation state by the reducing power method (RP) and ferric reducing antioxidant power assay (FRAP). Additional assays include the oxygen radical absorbance capacity (ORAC), for assessing radical chain-breaking ability through the inhibition of peroxyl radical (RO\({}_{2}\)\({}^{\bullet}\))-induced oxidation, and the trolox equivalence antioxidant capacity (TEAC), as well as the thiobarbituric acid reactive substances (TBARS) and \(\beta\)-carotene bleaching assays, to estimate the lipid peroxidation inhibitory capacity [24; 37; 38]. Among sag plants, _S. officials_ is the most widespread worldwide and also the most studied regarding antioxidant capacity [24; 39]. Due to their high antioxidant capacity, _S. officials_ polar phenolic extracts, usually alcoholic or hydroalcoholic extracts, are also frequently used as a reference to assess antioxidant properties of other less investigated plants [40; 41]. The DPPH EC\({}_{50}\) values (half maximal effective concentration, equivalent to the sample concentration that provides 50% of antioxidant activity) of distinct extracts from this species were established in the range of 1.98-10.1 \(\mu\)g/mL [42; 43; 41], being close to that of the flavonoid quercetin (2.79 \(\mu\)g/mL) [44]. The antioxidant activity of _S. officials_ phenolic-rich extracts has also been extensively assessed by the ABTS\({}^{\bullet}\) scavenging assay (EC\({}_{50}\) = 4.79-50.8 \(\mu\)g/mL) [43; 44], through evaluation of the ability to scavenge superoxide (EC\({}_{50}\) = 5.3-10.1 \(\mu\)g/mL) [42] and hydroxyl radicals (EC\({}_{50}\) = 1.36 \(\mu\)g/mL) [43], and also by the ORAC assay (0.4-1.8 mmol TE/100 mL) [45]. Moreover, methanolic extracts and decoctions of _S. officials_ were shown to exhibit very low EC\({}_{50}\) values, as estimated by \(\beta\)-carotene bleaching (EC\({}_{50}\) = 6.6 and 50.9 \(\mu\)g/mL, respectively) and TBARS assays (EC\({}_{50}\) = 2.1 and 10.4 \(\mu\)g/mL, respectively) [46]. More recently, Soxhlet extraction of _S. officials_ provided samples with high antiradical activity, with respective DPPH\({}^{\bullet}\) and ABTS\({}^{\bullet}\) EC\({}_{50}\) values of 116.5 and 88.2 \(\mu\)g/mL for aqueous extract, and 124.7 and 99.3 \(\mu\)g/mL for the hydroethanolic extract. Additionally, the authors showed that extracts obtained with a Soxhlet or by traditional methods presented a similar antioxidant activity against RO2\({}^{\bullet}\) (EC\({}_{50}\) values of 0.52 and 0.61 ug/mL for hydroethanolic and aqueous soxhlet extraction versus 0.52 and 0.69 ug/mL for hydroethanolic maceration and infusion traditional extraction, respectively) [47]. As for other _Salvia_ species, methanolic extracts of _Salvia_ from Tunisia origin (_Salvia aegyptiaca, Salvia argentea_ and _Salvia vertebraea_), were reported to scavenge DPPH\({}^{\bullet}\) (EC\({}_{50}\) = 21-77 ug/mL) and ABTS\({}^{\bullet}\) (141-318 u ME/mg DW), as well as to reduce the ferric form (81-164 mM Fe(II)/mg DW) [41]. Moreover, the DPPH EC\({}_{50}\) values of methanolchloroform (1:1) extracts of 14 _Salvia_ plants from South Africa, which in general contained rosmarinic acid as their major phenolic constituent, were shown to vary between 1.6 ug/mL (_Salvia schlectter_) and 74.2 ug/mL (_Salvia garipensis_) [48].