Modification and validation of Folin-Ciocalteu assay for faster and safer analysis of total phenolic content in food samples

Folin-Ciocalteu (F-C) is a routine assay in several laboratories around the world and has been widely employed for total phenolic content (TPC) quantification from food samples. F-C assay was modified to obtain a system reaction safer, as well as decrease the use of reagents, energy expenditure and time-consuming. After evaluating alternatives solvents and supports, and the effect of the binomial time/temperature, the modified F-C assay was as follows: 40% ethanol as solvent, 20 minutes at room temperature (25±2°C) using 50% F-C reagent and 5% sodium carbonate solution. The modified F-C assay was linear in 2.5-50.0 µg/mL range to gallic acid. Limit of detection and limit of quantification were 0.195 and 0.591 µg/mL, respectively. Intra-day and inter-day precision (relative standard deviation (RSD) 0.06-3.28%) and accuracy (93.28-104.28%) were also demonstrated. The assay was robust for F-C reagent (45-55%) and sodium carbonate (4.5-5.5%) changes. The modified assay was employed to analyse food samples containing phenolic compounds and the results corroborated with conventional assay. The modified F-C assay demonstrated to be reproducible, robust, fast, easy, inexpensive, safe and reliable for quantify phenolic compounds in food samples. The employment of ethanol in F-C assay decreases the environmental impact and, consequently, makes the analysis safer than conventional F-C assay. Furthermore, the modified F-C assay is conducted under milder conditions (time/temperature), which is particularly helpful for numerous analyses. Thus, the modified and validated F-C assay can be used as a routine assay in quality control and chemical profiling for natural product extracts and foods.