RESUMEN
ABSTRACT: 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 açaí 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 (R2 = 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 µg/mL and 33.1 µg/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 açaí seed extract, resulting in 38 g of pyrogallol equivalent/100 g of extract.
RESUMEN
Euterpe oleracea Mart. (Arecaceae) is an endogenous palm tree from the Amazon region. Its seeds correspond to 85% of the fruit's weight, a primary solid residue generated from pulp production, the accumulation of which represents a potential source of pollution and environmental problems. As such, this work aimed to quantify and determine the phytochemical composition of E. oleracea Mart. seeds from purple, white, and BRS-Pará açaí varieties using established analytical methods and also to evaluate it as an eco-friendly corrosion inhibitor. The proanthocyanidin quantification (n-butanol/hydrochloric acid assay) between varieties was 6.4-22.4 (w/w)/dry matter. Extract characterization showed that all varieties are composed of B-type procyanidin with a high mean degree of polymerization (mDP ≥ 10) by different analytical methodologies to ensure the results. The purple açaí extract, which presented 22.4% (w/w) proanthocyanidins/dry matter, was tested against corrosion of carbon steel AISI 1020 in neutral pH. The crude extract (1.0 g/L) was effective in controlling corrosion on the metal surface for 24 h. Our results demonstrated that the extracts rich in polymeric procyanidins obtained from industrial açaí waste could be used to inhibit carbon steel AISI 1020 in neutral pH as an abundant, inexpensive, and green source of corrosion inhibitor.