Carbon isotope analysis of bulk keratin and single amino acids from British and North American hair

Abstract

The reconstruction of ancient diets using isotopic measurements of bone collagen, and other tissues, which survive in archaeological contexts, relies on known isotopic relationships between diet and body tissues. Examination of these relationships often requires the study of modern human and animal subjects. While hair keratin can act as a useful proxy for bone collagen in isotopic studies on living humans, where it is inappropriate to sample tissues such as collagen, it can, in addition, act as a chronological indicator of dietary change. This study investigates hair keratin delta13C values from current residents of the UK and the USA. Residents in the USA showed a clear bulk hair delta13C enrichment of approximately 3 per thousand over UK individuals, attributed to an elevated C4 dietary input from maize fed to livestock in North America. The keratin delta13C of subjects who moved between the UK and USA showed a pronounced change after relocation, taking approximately 4 months to reach isotopic equilibrium. To investigate these differences further, we measured delta13C values of dispensable and indispensable amino acids as a group, and selected individual amino acids. As a group, enrichment of dispensable amino acids compared with indispensable amino acids occurred in samples from both continents, averaging 7.2 per thousand in the UK and 7.9 per thousand in the USA. Dispensable and indispensable amino acids, as well as all individual amino acids measured, were enriched in samples from the USA compared with those from the UK.

Analysis of amino acid 13C abundance from human and faunal bone collagen using liquid chromatography/isotope ratio mass spectrometry

“…Ion-pairing reagents, such as trifluoroacetic acid (TFA) and perfluorinated carboxylic acids, have been used in mobile phases to optimize separation efficiency but this also introduces extraneous carbon to the mobile phase. 18,31,32 In order to enhance ion-exchange and reversed-phase interactions the mixed-mode analytical column was chosen for method development. Mixed-mode columns provide a retention mechanism incorporating both ion-exchange and hydrophobic interactions with amino acids and the authors experimented with a number of stationary phases and low concentration acid mobile phases to manipulate the pH retention mechanism.…”

Preparative separation of underivatized amino acids for compound‐specific stable isotope analysis and radiocarbon dating of hydrolyzed bone collagen

“…Furthermore, the separate isotopic analysis of dispensable and indispensable (nonessential and essential) amino acids would make it possible to trace dietary components and nutrients from the environment into humans, useful for studies of diet. We are currently applying this methodology to the separation of amino acids from hair keratin [35], which will allow us to use living proxies for our study of ancient diet.…”

Reconstruction of breastfeeding and weaning practices using stable isotope and trace element analyses: A review

“…The assessment of biological age is relatively straightforward in soft tissues because the potential time lags between actual weaning ages and elemental signals are relatively small. The turnover rates of most soft tissues, such as blood, hair, nail, and muscle, and excreta are relatively high and these reflect diet during relatively short time periods (as little as a few days to months) before sampling for most animal species (e.g., O'Connell and Hedges, 1999;Sponheimer et al, 2003;McCullagh et al, 2005;Codron et al, 2011;Braun et al, 2013;Bahar et al, 2014).…”