Valorization of açaí (Euterpe oleracea Mart.) seed as a source of flavonoids: influence of different extractants and extraction techniques

Agro-industrial residues are promising sources of bioactive compounds, and their utilization contributes to the circular economy and to the reduction of environmental impacts. In this context, açaí (Euterpe oleracea Mart.) seed stands out, as it accounts for 85–95% of the fruit weight and shows potential as a source of phenolic compounds and flavonoids with antioxidant activity, which may be applied in the development of higher value-added products. However, the recovery of these compounds may be influenced by extraction conditions. Thus, this study aimed to evaluate the total flavonoid content (TFC) of açaí seed flour (ASF) extracts obtained using different extractants and extraction techniques. The seeds, donated by an açaí pulp processing industry in the state of Para, Brazil, were cleaned with potable water, sanitized with sodium hypochlorite (200 mg L⁻¹), dried in a forced-air circulation oven at 40 ± 2 °C for 72 h, ground in a knife mill, and standardized using a 60-mesh sieve. To obtain the extracts, 1.0 g of ASF was extracted with 8 mL of extractant under the following conditions: water with centrifugation (CA), citric acid-acidified water with centrifugation (CC), ethanol with centrifugation (CE), water with ultrasound (UA), citric acid-acidified water with ultrasound (UC), and ethanol with ultrasound (UE). TFC was determined by a colorimetric method, in which the extract was reacted with NaNO₂, AlCl₃, and NaOH, and absorbance was measured at 510 nm. Results were expressed as mg catechin equivalents per gram (mg CE g⁻¹) on a dry weight basis. Means were compared using Tukey’s test (p < 0.05), and different letters indicate significant differences among treatments. TFC ranged from 2.88 to 3.45 mg CE g⁻¹, with values of 3.45 ± 0.01^a (CA), 3.43 ± 0.01^a (CC), 2.88 ± 0.01^b (CE), 3.32 ± 0.01^ab (UA), 3.44 ± 0.01^a (UC), and 3.42 ± 0.01^a mg CE g⁻¹ (UE). The CE treatment showed the lowest content, differing significantly from CA, CC, UC, and UE, whereas UA did not differ from the other treatments. For water and acidified water as extractants, the extraction method did not significantly affect TFC. For ethanol, however, the use of ultrasound resulted in a higher content than that obtained with centrifugation (3.42^a vs. 2.88^b mg CE g⁻¹), which may be related to the greater release of these compounds from the matrix. Therefore, the results indicate that TFC recovery depends on the combination of extractant and extraction technique. ASF thus shows potential as a source of flavonoids, and its utilization may contribute to the valorization of this agro-industrial by-product and to circular economy strategies, enabling the production of higher value-added ingredients.