Abstract: The inter- and intra-crystalline fractions of Littorina littorea periwinkles recovered from archaeological sites in Northern Spain (covering the Azilian, Magdalenian and Solutrean periods) were examined for amino acid composition and racemisation over time. These fractions were found to be composed of similar proteins, as the amino acids and Asx D/L values were comparable and varied in the same way with increasing age and heating time. The protein loss from the inter-crystalline fraction was not highly significant after 22 ka and was lower than in other archaeological mollusc shells (Phorcus lineatus and Patella vulgata). The intra-crystalline fraction, isolated by bleaching, appeared to behave as a closed system for at least 22 ka, as reflected by the lack of a significant decrease in the amino acid content, although changes in the amino acid percentages occurred during this period. The percentage of aspartic acid remained almost constant with age both in the inter- and intracrystalline fractions. Good correspondence was obtained between Asx D/L values in unbleached and bleached samples and age, but discrimination of these archaeological periods within the last 27 ka using amino acid racemisation of L. littorea is unclear due to only slight differences between D/L values. We propose that temperature played a key role in the amino acid racemisation of L. littorea and could explain why in the localities that were formed during relatively cold conditions during the Lower Magdalenian (20.5?16.3 ka cal BP) and Solutrean (ca. 26.5?20.5 ka cal BP) periods, D/L values were similar and only slightly higher than in shells from sites formed during the Upper Magdalenian (16.3?13.5 ka cal BP).

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