# Antioxidant and Antimicrobial Properties of Selected Red Seaweeds from Central Portugal
## 4 Discussion
### Species-Specific Notes
crispus_ showed potential in the ABTS assay, presenting a low EC50 value, while, in the TPC assay, it had a polyphenol content comparable to most of the remaining seaweeds analyzed. In the MIC assay, _C. crispus_ extracts only inhibited _B. subtilis_ growth; furthermore, it is one of the species that required the highest concentration to induce such inhibition, from all the species analyzed. Nevertheless, the aqueous extracts show potential for further study, specifically in discovering which compounds are responsible for the measured bioactivities. _C. crispus_ is a well-known edible carrageenanophyte species, holding many benefits for human health, which includes having great bioactivity potential [44; 45; 46; 48]. The phenolic fraction of a number of carrageenanophyte species reportedly holds antimicrobial activity against fungi [80]. It is noteworthy, however, that _C. crispus_ stands as one example where the composition of a single compound, carraagenan (and consequent bioactivities it may hold), significantly varies between the tetrasporophyte and the gametophyte life stages, which are otherwise isomorphic [70]. Although the antioxidant activity of _S. coronopifolius_ stood among the average values unveiled for all seaweed species, both for the ABTS and the TPC assay, this red seaweed stood out as the one with the lowest MIC against _B. subtilis_ (although it failed to inhibit both _E. coli_ and _S. cerevisiae_ growth). _S. coronopifolius_ is a fairly well-studied seaweed in the academic context, although it remains to be as acknowledged as seaweeds such as _P. umbilicalis_ and _C. crispus_. Regarding its bioactive potential, _S. coronopifolius_ has been widely reported as a source of important metabolites with biological activity, namely antioxidant [81], antimicrobial [41], anti-inflammatory [82] and anti-tumoral activities [41; 50; 51; 82]. A previous study reported the noteworthy antimicrobial activity of _S. coronopifolius_ compared to a range of selected seaweed species, whose range of extracts with different solvents (_n_-hexane, dichloromethane and methanol) inhibit the growth of _S. cerevisiae_, while only the _n_-hexane extract inhibits the growth of _B. subtilis_ and, similarly to our study, showed no inhibition against _E. coli_[39]. Terpenes, commonly found in brown algae, but less so in red algae, have been isolated from _S. coronopifolius_ and targeted in several studies evaluating their potential as anti-cancer [51; 83; 84; 85; 86], antibiotic [87] and anti-fouling [88; 89; 90] agents. The variations found in the present study are probably explained by the different extraction method, where only aqueous extracts were tested. _P. cartilagenum_ is an algae that showed activity in both antioxidant and antimicrobial assays. Although the values achieved were not particularly outstanding, it presented polyphenols in amounts comparable to those found in the majority of the species analyzed. Similarly to the other species, it presented activity neither against _E. coli_ nor _S. cerevisiae_, but inhibited _B. subtilis_ growth. _P. cartilagenum_ lacks dedicated studies regarding its bioactivity potential, thus offering an opportunity to explore it further. Authors have shown the anti-proliferative activity of the dichloromethane extracts of _P. cartilagenum_[49] or studying the terpen _P. cartilagenum_ produces, with authors isolating and characterizing these compounds [91; 92; 93; 94]. A number of authors also found that the Antarctic _P. cartilagenum_, being completely adapted to polar environments, produces specific metabolites that can potentially be used in skin therapeutics [95]. The coralline algae (_C. officinalis_, _E. elongata_, _A. rigida_ and _J. rubens_) showed similar results in most analyses, and thus are discussed together. The whole group shows the lowest antioxidant activity by the ABTS assay when compared to all the other species analyzed. All coralline algae, except _J. rubens_, showed similar polyphenol quantities. Regardingantimicrobial activity, _C. officinalis, A. rigida_ and _J.