PREBIOTIC SELECTIVITY AND ANTIOXIDANT POTENTIAL OF ARABINOXYLANS FROM BREWER’S SPENT GRAIN ARE ENHANCED BY ULTRASOUND PROCESSING

Arabinoxylans (AX) derived from brewer’s spent grain (BSG) have attracted increasing interest as functional ingredients due to their prebiotic and antioxidant properties. However, their biofunctional performance is strongly influenced by their structural organization within the lignocellulosic matrix, which can limit their accessibility and biological activity. In this context, this study investigated the effect of ultrasound processing on the prebiotic selectivity and antioxidant potential of water-unextractable arabinoxylans (WUAX) obtained from BSG. WUAX were extracted under alkaline conditions using NaOH (0.5 mol L⁻¹) at a solid-to-solvent ratio of 1:10 (w/v), at 70 °C for 60 min. Ultrasound-assisted extraction (UAE) was performed in an ultrasonic bath (25 kHz, 300 W) and compared with conventional thermal extraction (CTE) under the same conditions. Prebiotic activity was evaluated in vitro using the prebiotic activity index (PAI), based on the selective growth of Lactobacillus rhamnosus, Lactobacillus acidophilus, and Lactobacillus plantarum, in comparison with Escherichia coli. The bioactive potential was assessed through total phenolic content (TPC) and antioxidant activity using FRAP, ABTS•⁺, and DPPH• assays. WUAX obtained by UAE exhibited significantly higher prebiotic activity than those extracted by CTE, with PAI values above 1.0 for all evaluated probiotic strains, whereas conventionally extracted samples showed reduced values and, for L. plantarum, a negative index. UAE promoted selective stimulation of probiotic growth while simultaneously limiting the proliferation of E. coli (≈ −0.21 log CFU mL⁻¹), indicating enhanced microbial selectivity. Among the tested strains, L. acidophilus showed the highest fermentative response. In addition to improved prebiotic performance, UAE significantly enhanced the bioactive profile of WUAX. The TPC increased by approximately 11% compared to the conventional method. This increase was directly reflected in antioxidant capacity, with improvements of about 18% (FRAP), 15% (ABTS•⁺), and 6% (DPPH•), indicating greater availability and accessibility of phenolic compounds associated with the polysaccharide structure. These enhancements are attributed to ultrasound-induced structural modifications, including disruption of the lignocellulosic matrix, reduction in particle size, and increased exposure of functional groups, which collectively improve enzymatic accessibility and interactions with reactive species. Overall, ultrasound processing emerges as an effective strategy to modulate the biofunctionality of arabinoxylans, enhancing both prebiotic selectivity and antioxidant capacity. These findings highlight the potential application of WUAX from BSG as multifunctional ingredients for the development of functional foods and gut health-promoting formulations.
 

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).