β-Glucan from Tibetan highland barley (THB) is an excellent edible gel polysaccharide due to its unique hypoglycemic and antioxidant activities. However, direct extraction of β-glucan from THB exhibits low yields with higher costs. Given that highland barley spent grain (BSG) is a byproduct of the brewing process and is frequently considered waste, the efficient extraction of its β-glucan could promote high-value repurposing of BSG. In this study, 2.74% β-glucan (BSG-B) was extracted from Rhizopus oryzae (R. oryzae)-fermented BSG, which is lower than those from THB (THB-B: 4.62%) yet enabled value-added utilization of BSG. The molecular weight of BSG-B was 5.24 × 10⁶ Da, which significantly increased by 124.89% compared to that of THB-B. Fourier-transform infrared (FT-IR) spectroscopy showed similar absorption peaks in BSG-B and THB-B, except for structural modifications in the β-glucan pyranose ring induced by the fermentation of R. oryzae. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicated that BSG-B possesses a more compact structure and lower aggregation heights compared to THB-B. Moreover, BSG-B demonstrated superior antioxidant capacities to THB-B in NO/DPPH/ABTS/reducing power assays, and lower apparent viscosity and oil adsorption capacity, likely attributed to the fermentation of R. oryzae. This study establishes a foundation for extracting higher-molecular-weight antioxidant β-glucan from BSG.

Gellan gum (GG) is an anionic microbial polysaccharide widely used in foods because of its efficient gelation, thermal stability, and ion-responsive structuring. However, the contrasting limitations of high- and low-acyl GG, together with their sensitivity to molecular weight, ions, pH, thermal history, and food-matrix composition, restrict their performance in complex products. This review distinguishes four intervention levels of GG modification and structural regulation: covalent modification, chain-architecture regulation, supramolecular regulation, and food-matrix composite structuring. These modifications and structural regulations alter chain properties, helix association, junction-zone formation, interfacial organization, and phase connectivity, thereby affecting gelation, texture, water retention, emulsion stability, processability, and release behavior. Food applications are evaluated through their structure–function relationships across diverse food systems. Particular attention is given to gastrointestinal disassembly, nutrient digestion, bioactive release, and colonic fermentation. Current evidence strongly supports the role of GG structural regulation in food texture and physical stability, whereas evidence for digestive modulation and physiological effects remains limited and is largely based on formulation-specific in vitro studies. Overall, this review provides a structure-guided framework for application-specific selection of GG intervention strategies.