Not all β-glucans are equal: processing-induced structural diversity of oat β-glucan and its functional and health outcomes.

Oats (Avena sativa) are a multifunctional cereal in which β-glucan is the primary bioactive component; however, its structural heterogeneity results in functionally non-equivalent fractions. This review demonstrates that β-glucan efficacy follows a continuum governed by weight-average molecular weight (Mw), rather than a binary classification. High-Mw fractions (>1000 kDa) are associated with viscosity-mediated cardiometabolic benefits, whereas low-Mw fractions (<300 kDa) promote fermentation-driven gut and immune responses. Intermediate Mw fractions (300-1000 kDa) provide overlapping functionality, contributing to both metabolic regulation and microbial fermentation. Processing conditions determine these structural transitions. Gentle thermal treatments such as steaming and kilning increase Mw from 1067 to 1713 kDa and from 75 to 1264 kDa, respectively, while enhancing viscosity (115 to 193 cP; 26 to 466.5 cP). Boiling maintains Mw within 1400-1900 kDa and increases extractability from 28% to 37%, while dehulling preserves native Mw. Moderate processing generates intermediate Mw fractions, with cryogenic milling reducing Mw from 2180 to ∼700 kDa and microfluidisation decreasing Mw from 2748 to 350 kDa while increasing solubility by up to 2.7-fold. Pulsed electric fields increase extractability by 94% with minimal Mw reduction (∼371 to ∼339 kDa). In contrast, intensive processing such as extrusion (down to 251 kDa), microwave treatment (1067 to 165 kDa), enzymatic hydrolysis (1000 to 104 kDa), and γ-irradiation (199 to 52 kDa) reduces Mw and viscosity, shifting functionality toward prebiotic and immune effects. Overall, not all β-glucans are equal; processing-induced structural diversity dictates functionality, highlighting the need for targeted Mw design to achieve specific health outcomes.