Lipopolysaccharide detection in foods using recombinant factor C and Toll-like receptor 4 activation assays

Lipopolysaccharides (LPS) are produced by gram-negative bacteria. Lipid A, with structural variants that determine its activity, is the component of LPS responsible for activating endotoxin assays and inducing inflammatory responses. The detection of LPS and Toll-like receptor 4 (TLR4)-dependent reporter activation in foods has received limited attention. The aim of this study was to quantify LPS in food and examine LPS mediated TLR4 stimulation in a subset of tested foods. Food and water samples (n=73) were examined in triplicate for LPS using the recombinant Factor C assay (rFC) assay. To determine the TLR4-dependent reporter activation, the human embryonic kidney (HEK)-Blue hTLR4 reporter cell assay was used. Foods were homogenized, centrifuged, and analyzed with and without filtration through a 0.45 µm PES-membrane filter. All foods had detectable quantities of LPS compared to none in water samples and were highest in mixed dishes (p < 0.001). There was a direct correlation between LPS detected in food samples using the rFC assay and hTLR4 reporter cell assay (r =0.779, p <0.05). LPS detected via TLR4-dependent activation suggests the presence of LPS with lipid A molecules with endotoxic activity. The methods described in this study provide guidance to measure LPS in future food studies needed to determine its relevance to health. • Endotoxins are a class of lipopolysaccharides (LPS) that bind the Toll-like receptor-4 and induce an inflammatory response. • There are exogenous sources of LPS, but food remains poorly characterized. • LPS was detected in 100% of foods tested including grains, fruits, vegetables, and protein foods and was highest in mixed dishes. • All foods tested, induced an LPS mediated inflammatory response. • Food LPS is an overlooked source of inflammation.