Alkaline cooking and stable isotope tissue-diet spacing in swine: archaeological implications

In this study we examine the effects of alkaline cooking on carbon and oxygen stable isotopic ratios of mineralized tissues from nine pigs raised on monotonous mixed C3/C4 vegetarian diets. Two sources of collagen (humerus and mandible) and two sources of apatite (humerus and enamel) were analyzed. Within each diet group, humerus and mandible collagens were found to record equivalent delta C-13 and delta O-18 ratios; however, enamel apatite was found to be enriched over bone apatite by 2.3 parts per thousand in carbon and 1.7 parts per thousand in oxygen. Alkaline cooking was found to slightly, but significantly increase the Delta C-13(collagen-diet) and Delta O-18(collagen-diet) of bone collagen. A similar trend towards enrichment was observed in bone and enamel Delta C-13(apatite-diet) and Delta O-18(apatite-diet), but the differences were not significant. Observed isotopic shifts were consistent with increased nutrient utilization of the alkaline-cooked maize as compared to raw maize. In addition, a reexamination of the relationship between diet and tissue carbon isotopic values suggests that species and alimentary type should be considered when interpreting ancient diets. (C) 2009 Elsevier Ltd. All rights reserved.