Proteomics analysis of ancient food vessel stitching reveals >4000-year-old milk protein.

RATIONALE: The 19th century excavation of an exceptionally well-preserved Early Bronze Age high status log-coffin burial from northern England, dated to 2200-2020 BC, yielded a 'food residue' collected from the inside of an accompanying bark vessel. This residue contained fibrous stitching that was used to hold the bark walls of the vessel together, first described as animal sinews, although the surviving material clearly contains animal hairs. Protein sequencing by soft ionisation mass spectrometry should identify the proteins that constitute the material, as well as the animal species from which they derive. METHODS: Peptide mass fingerprinting (PMF) by MALDI-TOF-MS combined with liquid chromatography-ESI-LTQ-MS/MS was used to identify low-abundance proteins as well as the dominant proteins in the sample. RESULTS: These proteomics techniques revealed the dominant proteins as deriving from the fibrous keratins (both types 1 and 2) and collagens (types 1 and 3), specifically those indicative of a bovine source. However, several peptide sequences diagnostic of bovine α-S1-casein were also observed, indicating that traces of milk had been preserved within the >4000-year-old fibrous residue. CONCLUSIONS: The presence of this food vessel that once contained milk within a burial of high status is suggestive of the importance placed on these secondary products. It is perhaps more remarkable that this information was retrieved not only from material of such antiquity, but also from an excavation that occurred nearly 200 years ago.