Alkali-Neutralization-Induced β-1,3-1,6-Glucan Nanoparticles Enhance the Aqueous Dispersibility, Stability, and Antioxidant Activity of Quercetin

Quercetin is a nutraceutical flavonoid whose aqueous use is limited by poor solubility and chemical instability. Existing polysaccharide carriers may require chemical modification, crosslinkers, multicomponent formulations, or complex processing. Here, alkali-neutralization-induced β-1,3-1,6-glucan nanoparticles (r-glucan NPs), prepared from Aureobasidium pullulans K-1 glucan, were compared with β-cyclodextrin (β-CD), using native t-glucan as a composition-matched control. Spectroscopic analyses supported quercetin association with chiral, cavity-rich domains of r-glucan NPs. r-Glucan NPs showed higher quercetin loading than β-CD and increased apparent aqueous solubility/dispersibility to 1620 ± 15.3 µM, compared with 256 ± 0.52 µM for the native β-1,3-1,6-glucan control, 347 ± 16.4 µM for β-CD, and 7.11 ± 3.97 µM for free quercetin. The t-glucan control initially retained quercetin but showed limited aqueous dispersibility and formed a visible precipitate within 3 days in 1 vol% ethanol. Although carrier association reduced oxygen radical absorbance capacity (ORAC) activity on an equal-quercetin basis, r-glucan NPs yielded a maximum ORAC value of 11,600 ± 1200 µmol TE L−1, compared with 815 ± 235 for β-CD and 368 ± 38.2 for free quercetin. r-Glucan NPs also improved apparent retention, photostability, stability at pH 6.8, and cellular antioxidant activity relative to free quercetin. These results support r-glucan NPs as food-compatible carriers for aqueous quercetin delivery.