L-tryptophan (Trp) is widely used in food and feed enforcement to play an important role in biological processes. Various metabolites of Trp perform its potent function. The indole pyruvate pathway is one of the main pathways of Trp metabolism in the gut microbiota, providing numerous indole-derivatives, which can modulate intestinal homeostasis and mucosal immunity by activating the aryl hydrocarbon receptor (AHR) signaling pathway. In this study, we constructed an IL4I1-overexpressed 293T cell line and found that IL4I1 can catalyze Trp to produce indole-3-acetic acid (IAA) and indole-3-carboxaldehyde (IAld). Moreover, both IAA and IAld are accumulated in dendritic cells (DCs) and can stimulate the expression of CYP1A1. Our results demonstrate the existence of the indole pyruvate pathway in host cells with IL4I1 as the key enzyme. The IL4I1-mediated Trp metabolism implies the role of dietary impact on immunity.

BACKGROUND The illegal undeclared addition of reconstituted milk powder to ultra‐heat treated (UHT) milk to lower production costs is an example of economically motivated adulteration. This activity not only defrauds consumers but also places honest traders at a disadvantage, which could damage the reputation of milk producers and reduce the integrity of the markets. In this research, a non‐targeted analytical strategy that combines proton (1H) nuclear magnetic resonance (NMR) spectroscopy with a chemometrics data mining tool was developed for the authentication of bovine UHT milk. RESULTS Unsupervised principal component analysis was used to distinguish UHT and tap‐water‐reconstituted powdered milk. Partial least squares‐discriminant analysis (PLS‐DA) with R2(Y) and Q2 equal to 0.859 and 0.748, respectively, was used to differentiate UHT and reconstituted milk samples. Three compounds were selected as biomarkers to distinguish UHT and reconstituted milk and identified according to the standard NMR‐spectra database. Finally, a PLS‐DA model was established, according to the characteristic spectral bands, to identify UHT milk and reconstituted milk. CONCLUSION This procedure demonstrated the feasibility of using non‐targeted NMR profiling combined with chemometric analysis to combat mislabeling and fraudulent practices in milk production. © 2019 Society of Chemical Industry

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