Katja Parschat: Conceptualization, Project administration, Writing - Review & Editing, Anne Oehme: Data curation, Writing - original draft, Jost Leuschner: Methodology, Investigation, Stefan Jennewein: Conceptualization, Supervision, Julia Parkot: Conceptualization, Project administration, Writing - review & editing, SupervisionA safety evaluation of mixed human milk oligosaccharides in rats.

Human milk oligosaccharides (HMOs) are indigestible carbohydrates representing the third largest fraction of solutes in human breastmilk. They provide valuable prebiotic and anti-pathogenic functions in breastfed infants, but are not yet included in most infant formula products. Recent biotechnological advances now facilitate large-scale production of HMOs, providing infant formula manufacturers with the ability to supplement their products with HMOs to mimic human breastmilk. Although the safety of individual HMOs has been confirmed in preclinical toxicological studies, the safety of HMO mixtures has not been tested. We therefore performed bacterial reverse mutation and in vitro micronucleus tests and conducted a repeated-dose oral toxicity study in rats with a mixture of five HMOs (HMO MIX I), containing 2'-fucosyllactose (2'-FL), 3-fucosyllactose (3-FL), lacto-N-tetraose (LNT), 3'-sialyllactose (3'-SL) and 6'-sialyllactose (6'-SL). HMO MIX I was not genotoxic and did not induce adverse effects in the repeated dose study. The no-observed-adverse-effect-level (NOAEL) for HMO MIX I in this study is 10% in the diet (equivalent to 5.67 g HMO MIX I/kg bw/day for males and 6.97 g HMO MIX I/kg bw/day for females). Our results provide strong evidence for the safety of HMO MIX I in infant products and general foods.