PREBIOTIC POTENTIAL OF EXOPOLYSACCHARIDES OBTAINED FROM AN AÇAÍ BEVERAGE FERMENTED BY SONICATED WATER KEFIR

Microbial exopolysaccharides (EPS) have been investigated as functional ingredients due to their partial resistance to digestion and selective utilization by gut microorganisms. Ultrasound-assisted fermentation may modify EPS production and functionality, improving bioaccessibility and fermentability. This study evaluated the prebiotic potential of EPS extracted from açaí beverage fermented by water kefir grains subjected to ultrasonic pretreatment. Kefir grains were sonicated at 500 W and 19 kHz for 5 min, corresponding to an acoustic intensity of 75.4 W.cm⁻², and used to ferment açaí juice for 24 h at 30 ± 3 °C. After fermentation, EPS were recovered by alcoholic precipitation and freeze-dried. Two samples were obtained: EPS-US, from the beverage fermented with sonicated grains, and EPS-C, from the beverage fermented with non-sonicated grains. Fructooligosaccharide (FOS) was used as a commercial prebiotic control. EPS-US, EPS-C, and FOS were subjected to simulated gastrointestinal digestion according to INFOGEST 2.0. Prebiotic potential was assessed through the growth of Lacticaseibacillus casei NRRL B-442, Bifidobacterium bifidum NRRL B-41408, and Bifidobacterium infantis NRRL B-41661 over 48 h, considering microbial counts, absorbance-based growth, EPS consumption, and biomass yield coefficient (YX/S), which represents substrate conversion into biomass. The prebiotic effect was strain-dependent. For L. casei, EPS-US showed the best performance after 24 h, with higher substrate consumption and a YX/S value of (0.1646), exceeding EPS-C and FOS. For B. bifidum, EPS-US also presented the highest overall YX/S value (0.2681), indicating more efficient polymer utilization for biomass formation, although EPS-C resulted in higher microbial counts after 48 h. For B. infantis, the response was more variable, with the highest YX/S observed for EPS-C however, EPS-US showed marked substrate consumption within the first 24 h, suggesting metabolic utilization of the polymer. Overall, EPS from açaí beverage fermented with sonicated kefir grains exhibited relevant prebiotic performance, particularly for L. casei and B. bifidum, with effects comparable or superior to FOS. These findings support ultrasound as a technological tool in fermentation processes, possibly due to cavitation-induced structural modifications in EPS, such as reduced molecular weight, increased solubility, or greater exposure of glycosidic bonds. Therefore, these EPS show potential as non-conventional prebiotics for plant-based functional foods.