ULTRASOUND-ASSISTED EXTRACTION ENHANCES KINETIC PERFORMANCE AND YIELD OF ARABINOXYLANS FROM BREWER’S SPENT GRAIN

Brewer’s spent grain (BSG) is an abundant lignocellulosic residue rich in arabinoxylans (AX), whose recovery is limited by the strong structural association of these polysaccharides within the plant cell wall matrix. Despite their potential as functional ingredients, the efficient extraction of the water-unextractable fraction (WUAX) remains a technological challenge, requiring process intensification strategies. In this context, the objective of this study was to evaluate the effect of ultrasound-assisted extraction (UAE) compared with conventional thermal extraction (CTE) on the extraction kinetics and yield of WUAX from BSG. Extractions were performed using NaOH solution (0.5 mol L⁻¹) at a solid-to-solvent ratio of 1:10 (w/v), at temperatures of 30, 50, and 70 °C for up to 60 min. UAE was conducted in an ultrasonic bath (25 kHz, 300 W), while CTE was carried out in a thermostatic water bath. After extraction, the extracts were neutralized, precipitated with ethanol, and centrifuged to obtain the WUAX fraction. Quantification was performed using a phloroglucinol-based colorimetric method, and extraction kinetics were described using a first-order model. WUAX extraction exhibited typical diffusion-controlled behavior, characterized by a rapid initial phase (20–30 min) followed by an equilibrium plateau (WUAX∞). The kinetic model showed excellent fit to the experimental data (R² ≥ 0.97). Increasing the temperature from 30 to 70 °C significantly enhanced extraction parameters. Under CTE, WUAX∞ increased from 0.76 to 3.15 g/100 g, with WUAX₆₀min reaching 3.23 g/100 g and a yield of 32.4%. Under the same conditions, UAE showed superior performance, achieving WUAX∞ of 3.60 g/100 g, WUAX₆₀min of 3.83 g/100 g, and a maximum yield of 38.6%. The kinetic constant (k) increased from approximately 0.05–0.06 min⁻¹ at 30 °C to 0.09 min⁻¹ at 70 °C, indicating improved kinetic favorability at higher temperatures. UAE promoted more pronounced increases in the extraction plateau than in the kinetic constant, indicating that its primary effect is associated with enhanced structural accessibility of AX rather than solely accelerating mass transfer. This behavior is attributed to acoustic cavitation, which induces microfissures in the cell wall, increases the solid–liquid interfacial area, and facilitates solvent penetration, promoting the partial disaggregation of AX–lignin complexes. The low values of WEAX₆₀min (0.11–0.22 g/100 g) confirm the predominance of insoluble fractions in BSG. In conclusion, UAE improves extraction efficiency mainly by enhancing AX structural accessibility, enabling higher yields under moderate conditions (70 °C, 60 min, 0.5 mol L⁻¹ NaOH). These findings highlight the potential of ultrasound as a sustainable technology for valorizing agro-industrial residues into high-value functional ingredients.
 

Acknowledgments

This study was supported by CAPES (Finance Code 001), FAPEMIG (APQ-00388-21; APQ-00785-23; APQ-06600-24; RED-00157-23), and FINEP (01.23.0632.00).