A validated Folin-Ciocalteu method for total phenolics quantification of condensed tannin-rich acai (Euterpe oleracea Mart.) seeds extract

The widely used methodology to quantify polyphenols-the Folin-Ciocalteu (FC) method-cannot be applied indiscriminately since different matrices may impair the assay's accuracy. Thus, this study aimed to adapt the FC method for the acai seed extract, a tannin-rich extract with potential applications for various therapies. Firstly, a pre-method standardization was established to determine parameters such as reading wavelength (765 nm), reaction time (30 min), and the reference substance (pyrogallol). In the validation step, the adapted method responded linearly to the analyte (R-2 = 0.9910), ensuring its selectivity (linearity and selectivity curves statistically parallel) and accuracy (99.18-101.43%). Furthermore, the method proved to be precise (RSD <= 2.63%) at the two levels assessed (repeatability and intermediate precision) and robust (RSD <= 4.45%) concerning variation on the Na2CO3 concentration and the reaction time. The limits of detection and quantification were also calculated (9.9 mu g/mL and 33.1 mu g/mL, respectively). An additional step for tannins quantification based on its reported selective precipitation by complexing agents was also evaluated; however, unspecific precipitation was observed, reducing the results' accuracy. Our work successfully adapted and validated a method for total phenolics quantification of acai seed extract, resulting in 38 g of pyrogallol equivalent/100 g of extract. Graphic abstract

Automated summary

The study successfully adapted and validated the FC method for quantifying total phenolics in acai seed extract, with a result of 38 g of pyrogallol equivalent/100 g of extract. The method showed linear response to the analyte, good selectivity, accuracy, precision, and robustness, with limits of detection and quantification determined. An additional step for tannins quantification based on selective precipitation was evaluated but found to reduce accuracy.