Comprehensive evaluation of Folin-Ciocalteu assay for total phenolic quantification in algae (Chlorophyta, Phaeophyceae, and Rhodophyta)

Abstract

The Folin-Ciocalteu assay is a tool widely employed to measure total phenolic content (TPC) in various applications across different fields, including food industry, agriculture, medicine, and environmental sciences. However, despite its popularity, there are limitations and an ongoing debate concerning its accuracy in TPC measurement. This review addresses these concerns within the context of phycology. A comprehensive database was compiled to quantitatively and qualitatively analyze the use of the Folin-Ciocalteu assay in this field. The quantitative approach led to the creation of an activity scale, indicating that brown algae, with their phlorotannins, and green microalgae stand out within the algal groups. Moreover, the qualitative approach indicates that the assay has proven to be a sensitive tool for studying algal ecology and physiology, and it has been widely employed to evaluate the biotechnological potential. However, a critical analysis reveals concerns related to interfering non-phenolic compounds and insufficient information on data reporting, including imprecise language and undefined terms, which hinders comparison with literature. Despite the growing interest in the Folin-Ciocalteu assay, most articles (98.7 %) do not take into account the effect of interfering compounds on TPC determination. Thus, the Folin-Ciocalteu assay is used as a measure of reducing power or antioxidant capacity in phycology rather than a measure of TPC. Nevertheless, with proper consideration of limitations, the Folin-Ciocalteu assay remains a valuable tool due to its simplicity, cost-effectiveness, and sensitivity.