Stable oxygen isotopes in water of concentrated liquid foodstuffs: Are the commonly determined values accurate?

RATIONALE: Oxygen isotope analysis of water molecules of liquid foodstuffs is commonly performed under isotopic equilibrium between water in the solution and the vapour water, assuming that the liquid water activity is equal to unity and that liquid water is an ideal mixture of H2 O isotopologues. A priori this behaviour is not realistic for all foodstuffs, which frequently are very concentrated solutions. In this paper we mainly consider "balsamic vinegar" with the aim of defining an appropriate procedure of oxygen isotope ratio analysis of water molecules in these concentrated solutions. METHODS: Isotope ratio mass spectrometry (IRMS) measurements of the oxygen isotope ratios (δ18 O values) were carried out on CO2 equilibrated with water molecules at 22 ± 0.1°C. Three independently calibrated, very low salinity waters were used as standards. RESULTS: For grape must and wine vinegar (density < 1.15 g/cm3 ) the δ18 O values for water determined directly on these solutions are "true" values. On the contrary, for balsamic vinegar with density higher than 1.15-1.20 g/cm3 , the δ18 O values obtained directly on the solutions are systematically different from those obtained on water produced by distillation of the same samples at 70°C under vacuum. CONCLUSIONS: In the case of balsamic vinegar with density higher than 1.15-1.20 g/cm3 , to avoid severe systematic errors, the isotopic analyses must be carried out on water obtained by distillation under stirring.

Stable isotope study on ancient populations of central sudan: Insights on their diet and environment.

OBJECTIVES: A contribution to the knowledge of the economy and the environmental surroundings of the populations living along the Nile valley in three different periods. MATERIALS AND METHODS: This study reports stable isotope analyses on apatite bone samples of 139 humans, 48 mammals, and 43 fish from the Al Khiday archaeological sites in Sudan. The bones belong to four archaeological periods: pre-Mesolithic, Mesolithic, Neolithic, and Meroitic. Data were processed statistically. RESULTS: A significant difference exists between the pre-Mesolithic and Mesolithic mean δ(18) Ow value and the mean of the modern Nile. The mean δ(18) Ow values for the Neolithic humans and bovids are very similar (+1.5‰ ±4‰, and -2‰, respectively) and more positive than the mean values of Mesolithic mammals and Pre-Mesolithic humans. The water ingested by Meroitic humans (+7‰ ± 2.5‰) is enriched in (18) O in respect to the water ingested by the Neolithic population. There is a separation in the δ(13) Cdiet values between the pre-Mesolithic humans (-14‰ ± 1‰) and Mesolithic mammals (-12‰ ± 2‰) group and the Neolithic humans (-18‰ ± 1‰), Meroitic humans (-19‰ ±1‰), Neolithic mammals (-21‰), and the modern (mean δ(13) Cdiet = -19‰ ±2‰) mammal group. DISCUSSION: The climate became warmer and more arid from the pre-Mesolithic/Mesolithic to the Meroitic period. The environmental conditions influenced the strategies of subsistence and, in particular, the changes occurring from the pre-Mesolithic to the Neolithic can be considered contemporaneous to the transition from hunting-gathering-fishing to cultivation-herding. Am J Phys Anthropol 160:498-518, 2016. © 2016 Wiley Periodicals, Inc.