Upcycling Agro-Industrial Biomass into Bioactive Oligosaccharides for the Circular Bioeconomy: Beyond the Prebiotic Effects with a Focus on Receptor Interactions

Oligosaccharides represent an important class of bioactive compounds with diverse structure-dependent functionalities. While traditionally investigated for prebiotic effects on gut microbiota, increasing evidence shows that they can also interact directly with intestinal and immune cell receptors (e.g., pattern recognition receptors, C-type lectin receptors, G-protein coupled receptors, and scavenger receptors), influencing inflammation, mucosal immunity, and epithelial barrier function. In a circular bioeconomy context, oligosaccharides offer an underexplored sustainable route for upcycling agro-industrial and forestry biomass by converting polysaccharides into structurally tailored products. This review synthesizes current knowledge on the direct effects of plant-derived oligosaccharides on host receptors and describes enzymatic and green chemistry-based methods for their production and extraction. We propose a new roadmap for oligosaccharide upcycling using assessments for their biological effects, characterization, standardization, and alignment with regulatory aspects. This enables translating receptor-active oligosaccharides from biomass utilization into innovative solutions for precision nutrition and sustainable functional food development.