Organ-specific toxicity of Maillard-derived 2-furfural and 5-hydroxymethylfurfural: Quantitative evidence from zebrafish

The Maillard reaction enhances flavor in thermally processed infant formula (IF) yet generates furfural derivatives such as 2-furfural and 5-hydroxymethylfurfural (5-HMF), raising safety concerns. This study assessed the toxicity of these compounds using both wild-type and transgenic zebrafish models, while establishing quantitative concentration-specific toxicity relationships. Stored IF produced elevated levels of 2-furfural and 5-HMF compared to normal IF, leading to immune, nervous, and liver toxicity in exposed zebrafish. Both compounds induced immunotoxicity at maximum non-lethal concentrations and hepatotoxicity across tested doses. Notably, 5-HMF showed minimal neurotoxicity and gastrointestinal (GI) effects, while 2-furfural induced neurotoxicity at its lowest concentration and GI toxicity at 10 % lethal concentration (LC 10 ). Moreover, high levels of these compounds in powdered IF can elicit immune, hepatic, and neurotoxicity, but not GI toxicity, with differences from pure compounds likely attributable to the influence of the complex dairy matrix. To our knowledge, this is the first study using the zebrafish model to systematically evaluate the immunotoxicity, neurotoxicity, hepatotoxicity and GI effects of 2-furfural and 5-HMF, and to establish quantitative, concentration-dependent, organ-specific toxicity relationships. These findings reveal the safety risks of these Maillard-derived compounds and highlight the need to optimize thermal processing to reduce their formation and improve infant-formula safety.