Extremely oxygen-sensitive next-generation probiotics: can current microcomposite formulations ensure effective colonic delivery?

This narrative review evaluates the suitability of conventional biopolymer-based microencapsulation strategies, originally developed for facultative and aerotolerant probiotics, for the protection and delivery of extremely oxygen-sensitive (EOS) next-generation probiotics (NGPs). With increasing interest in NGPs, there is a pressing need to establish whether conventional formulation approaches can be effectively translated for these highly oxygen-sensitive bioactives. We reviewed commonly used microencapsulation materials and techniques, assessing their suitability and potential to preserve EOS bacterial viability. Hydrated pectin- and gellan-based microcomposite systems, particularly when combined with xanthan gum or other polymers, exhibited the strongest oxygen-protection performance. In contrast, alginate alone demonstrated inconsistent barrier properties, though its performance improved when blended or coated with chitosan. Dehydrated microcomposite systems did not yield additional viability benefits compared to their hydrated counterparts. Importantly, none of the studies explicitly quantified oxygen exposure parameters or established threshold levels required for effective protection of EOS strains. Despite some microcomposite systems demonstrating potential for EOS colonic delivery, our findings highlight a critical gap in formulation science for these sensitive bioactives and underscore the need for the development of bespoke, tailored delivery systems that advance beyond conventional approaches designed for facultative or aerotolerant strains. Addressing these gaps will support the advancement of microencapsulation technologies, improve biotherapeutic NGP formulation, and ultimately facilitate the translation of exploratory clinical findings into rationally designed, accessible, and effective microbiome-based interventions.