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Lipid analysis goes to pot
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A combination of MS methods has demarkers of animal fats. Seven vessels fell They then plotted the relative intensity of termined that fat residues in three Neointo the large distribution class because each fatty acid peak against carbon numlithic pots came from goat’s milk, cow’s ber. These plots, which indicated how their TAGs exhibited a wide range of sizes (T40 to T54, where the subscript much of a fatty acid with say, 12 carbon milk, and sheep meat. In the August 15 issue of Analytical Chemistry (pp 6182– indicates the number of carbon atoms atoms, was present in a particular sample, served as signatures for milk fat and adi6192), Martine Regert and colleagues in a TAG, excluding the three in the describe a new approach to identifying pose fat from cows and goats. For examglycerol backbone). Another seven fell types of food and their animal sources into the medium distribution class, T44 ple, T46 from bovine adipose tissue conin ancient ceramic vessels, which in this to T54, and four others fell into the nar- tained only four saturated fatty acids (C12 case were 5000–6000 to C18), whereas T46 from years old. The work was bovine milk fat contained 60 T44:0 Goat’s milk performed at the Censix (C10 to C20). Many feaCow’s milk tures distinguished goat’s tre de Recherche et de 50 milk from cow’s milk. For Restauration des MuT1050A instance, only goat’s milk sées de France and the 40 had C18 in its T24, and Université des Sciences 150 0 10 cm only cow’s milk had C20 in et Technologies de Lille 30 its T40. (France). “By combining The collaborators GC/MS with nanoESI 20 searched for these sigMS, it has been possible to determine new criteria natures in four ancient 10 for distinguishing species vessels. High-temperature that were exploited for GC and GC/MS readily 0 dairy products or meat,” identified degraded dairy C6:0 C8:0 C10:0 C12:0 C14:0 C16:0 C18:0 C20:0 products in two vessels. Regert says. Moreover, nanoESI MS Previously, milk lipids A plot of the relative intensities of fatty acids liberated from TAGs during could be differentinanoESI-MS/MS versus carbon number shows that the T44 derived from one of on one of these vessels ated from meat lipids the Clairvaux vessels matches the signature of cow’s milk (red) and not that of detected T28, which had in ancient pots, but the goat’s milk (green). eluded previous investigaanimals that produced tions because of its small those lipids could not be identified, row distribution class, T46 or T48 to T54. size and low concentration. By obtaining especially in the case of dairy products. After a literature search, the researchers nanoESI MS data for various TAGs and equated the large distribution class with comparing features such as carbon numRegert attributes the group’s success degraded dairy products and the narrow ber, fatty acid distribution, and number to advances in MS and the level of distribution class with subcutaneous fat. of unsaturated bonds, the researchers preservation of the pots, which Pierre showed that one vessel had contained The source of the TAGs in the medium Pétrequin’s team excavated from under distribution class was unclear. goat’s milk and the other cow’s milk. Lakes Clairvaux and Chalain in eastern To find criteria for identifying milk or GC/MS shed no light on the third France, where oxidation and bacterial degradation are minimal. meat from different animal species, samvessel, but nanoESI MS showed that it had contained subcutaneous fat, probGraduate student Sigrid Mirabaud ples were taken to Christian Rolando for selected shards of pots that were covanalysis with nanoESI MS and nanoESI- ably from sheep. The contents of the ered with carbonized residues, which fourth remained a mystery, even with MS/MS. These methods were tested by impregnating modern pot pieces with always contain fat. After mechanically nanoESI MS analysis. washing the shards to avoid contaminamilks or fats. NanoESI MS proved to “For the first time, it is possible on tion, she ground them up and extracted be much more sensitive than high-temsuch degraded samples to determine and derivatized the lipids. The samples the animal species from which milk was perature GC/MS, detecting even small were then screened by high-temperature TAGs (T24 and T26) in the samples. exploited,” Regert says. “So it opens up new avenues for the archaeological inGC/MS for meat fat, dairy products, The researchers used a nanoESI quadand other food remains. terpretation of the exploitation of these rupole TOF mass spectrometer to deterThis approach identified three classes mine the number of carbon atoms and natural systems by Neolithic people.” a —Linda Sage of triacylglycerols (TAGs)—specific bio- double bonds in each TAG’s fatty acids. s e p t e m b e r 1 , 2 0 0 7 / A n a ly t i c a l C h e m i s t r y
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