Total phenolic content in brown algae from the Sicilian coast

Abstract

Phlorotannins are polyphenolic secondary metabolites found in almost all brown algae that function as defense against grazers, pathogens and epiphytes but are also involved in photoprotection mechanisms. These com- pounds, produced in the Golgi apparatus, are accumulated in cytoplasm, within vesicules called physodes, or bound to the cell wall. The concentration of phlorotannins differs within and between species, shows geograph- ical variations but may be also affected by abiotic or biotic factors. We present here an overview of the studies carried out on total phenolic content in brown algae collected along the north-western coast of Sicily. The aims of these studies were in particular a) to analyse total phenolic content in four Mediterranean brown algae (Cys­ toseira amentacea, Cystoseira compressa, Dictyopteris polypodioides and Padina pavonica), b) to follow the sea- sonal changes in total phenolic content in D. polypodioides and C. amentacea and c) to test the effects of temperature on total phenolic content of C. amentacea. Results showed signiicant differences in total phenolic content between leathery and sheet-like algae and also within each morphological group. Among the four species, the sheet-like alga D. polypodioides showed the highest concentration of phenolic compounds. Differ- ences in the seasonal pattern of total phenolic content and in the period of maximum production were observed between D. polypodioides and C. amentacea. In D. polypodioides the peak was observed during winter and autumn whereas for C. amentacea the peak was observed during spring and summer. Moreover, C. amentacea responded signiicantly to the exposition to an increase of temperature, suggesting that increasing global temperatures predicted in the coming century might have effects on the chemical defences and then on the trophic interactions of these algae. The results of these studies seem to conirm that total phenolic content in brown algae is a re- sponse to a combination of several factors. However, due to the complexity of total phenolic content responses in brown algae and the multiple roles of phlorotannins, for a better understanding of this process, it is still nec- essary to identify which types of phlorotannins are responsible for the different activities in order to clarify who does what. Therefore, studies are currently in progress in order to characterize phlorotannins in some species belonging to the Fucales and Dictyotales and to test their biological activities.