ULTRASOUND AMPLITUDE MODULATES PARTICLE PROPERTIES AND PHENOLIC RECOVERY FROM AÇAÍ SEEDS

Açaí (Euterpe oleracea Mart.) processing generates large amounts of seeds containing compounds of functional interest. Ultrasound-assisted processing may improve the release of phenolic compounds from this residue; however, acoustic cavitation can also modify the particle-size distribution and colloidal properties of the resulting dispersions. This study evaluated the effects of ultrasound amplitude on the hydrodynamic diameter, polydispersity, zeta potential, and total phenolic content of aqueous açaí seed dispersions. Açaí seeds were blended with water at a 1:1 seed-to-water ratio for 5 min and filtered. The dispersions were treated for 5 min using a BIOBASE UCD-650 ultrasonic processor (650 W, 25 kHz) at amplitudes of 20, 40, and 60%. A non-sonicated dispersion was used as the control. Hydrodynamic diameter, polydispersity index, and zeta potential were determined using a Litesizer 500 analyzer (Anton Paar). Total phenolic content was quantified by the Folin–Ciocalteu method using gallic acid as the reference standard and expressed as mg gallic acid equivalents per liter (mg GAE L^-1). Data were evaluated by one-way analysis of variance and Tukey’s test at 95% confidence. Ultrasound increased the hydrodynamic diameter compared with the control, which presented a mean diameter of 1583.93 nm. Values of 2183.00, 2263.13, and 2785.31 nm were obtained at 20, 40, and 60%, respectively. The increase at the highest amplitude suggests that intense cavitation favored particle collision, structural disruption, and reaggregation of insoluble components. The polydispersity index ranged from 23.64 to 27.77% and was not significantly affected, indicating similar dispersion heterogeneity among treatments. The control showed the most negative zeta potential (−18.87 mV), whereas sonicated samples ranged from −14.00 to −14.58 mV. This reduction in surface-charge magnitude indicates weaker electrostatic repulsion and is consistent with the formation of larger aggregates. In contrast, ultrasound markedly enhanced total phenolic recovery. The control contained 3524.33 mg GAE L^-1, while treatments at 20, 40, and 60% reached 6096.39, 5930.69, and 5815.41 mg GAE L^-1, corresponding to increases of 73.0, 68.3, and 65.0%, respectively. Although ultrasound amplitudes did not differ significantly in phenolic content, the 20% treatment produced the highest numerical value and a smaller hydrodynamic diameter than the 60% treatment. Therefore, low-amplitude sonication was the most favorable condition, improving phenolic extraction while limiting particle aggregation and energy input. These results demonstrate the potential of ultrasound for valorizing açaí seeds and show that amplitude must be controlled to balance extraction efficiency and colloidal characteristics.

The authors gratefully acknowledge the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação Araucária (FA), Instituto Federal do Paraná (IFPR), and Universidade Estadual de Maringá (UEM) for their financial and institutional support. The authors also acknowledge the Complexo de Centrais de Apoio à Pesquisa (COMCAP/UEM) for providing the facilities and technical support required for the analyses.