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 (M w ), rather than a binary classification. High-M w fractions (>1000 kDa) are associated with viscosity-mediated cardiometabolic benefits, whereas low-M w fractions (<300 kDa) promote fermentation-driven gut and immune responses. Intermediate M w 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 M w 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 M w within 1400–1900 kDa and increases extractability from 28% to 37%, while dehulling preserves native M w . Moderate processing generates intermediate M w fractions, with cryogenic milling reducing M w from 2180 to ~700 kDa and microfluidisation decreasing M w from 2748 to 350 kDa while increasing solubility by up to 2.7-fold. Pulsed electric fields increase extractability by 94% with minimal M w 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 M w 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 M w design to achieve specific health outcomes.