Microbial Levan for food applications: From process-dependent heterogeneity to specification-led functionality

Microbial levan is a β-(2 → 6)-fructan whose recovered form is shaped jointly by biosynthesis and downstream processing. Preparations can differ in molar-mass distribution, branching, conformation, aggregation, residual sugars, proteins and recovery history, so materials carrying the same name are not necessarily functionally interchangeable. This critical review evaluates how levansucrase catalysis, fermentation, recovery and analytical choices define the test article used in food studies. Within-study comparisons support preparation-specific associations with rheology, water retention, emulsion behaviour, digestive fate and biological responses, whereas cross-study contrasts often confound polymer architecture with producer, purification, analytical platform and aggregation. We therefore present a specification-led qualification workflow in which intended use defines minimum identity, candidate material attributes, manufacturing levers, provisional release measures and claim-matched validation. The framework distinguishes technical performance from prebiotic or health-claim substantiation and requires the same recovered batch to be characterized and tested whenever causal structure-function inference is attempted. Current evidence supports preparation-specific qualification, not transfer of performance, safety or health claims to levan as a material class.