Ruminant meat and milk contain δ-valerobetaine, another precursor of trimethylamine N-oxide (TMAO) like γ-butyrobetaine

•δ-Valerobetaine is reported for the first time in ruminant meat and milk.•δ-Valerobetaine is more abundant in meat and milk of ruminants than non-ruminants.•δ-Valerobetaine originates in the rumen from Nε-trimethyllysine.•δ-Valerobetaine, producing trimethylamine in the gut, could be a health risk factor.•δ-Valerobetaine highlights the importance of Nε-trimethyllysine in vegetables. Quaternary ammonium compounds containing N-trimethylamino moiety, such as choline derivatives and carnitine, abundant in meat and dairy products, are metabolic precursors of trimethylamine (TMA). A similar fate is reported for Nε-trimethyllysine and γ-butyrobetaine. With the aim at investigating the metabolic profile of such metabolites in most employed animal dietary sources, HPLC-ESI-MS/MS analyses on ruminant and non-ruminant milk and meat were performed. Results demonstrate, for the first time, the presence of δ-valerobetaine, occurring at levels higher than γ-butyrobetaine in all ruminant samples compared to non-ruminants. Demonstration of δ-valerobetaine metabolic origin, surprisingly, showed that it originates from rumen through the transformation of dietary Nε-trimethyllysine. These results highlight our previous findings showing the ubiquity of free Nε-trimethyllysine in vegetable kingdom. Furthermore, δ-valerobetaine, similarly to γ-butyrobetaine, can be degraded by host gut microbiota producing TMA, precursor of the proatherogenic trimethylamine N-oxide (TMAO), unveiling its possible role in the biosynthetic route of TMAO.