Potentials and caveats with oxygen and sulfur stable isotope analyses in authenticity and origin checks of food and food commodities

The sulfate reduction in plants is accompanied by isotope fractionation but as normally no sulfur is excreted, the δ34S value of bulk plant matter is identical to that of the primary local source. Small differences in the δ34S values of plant compartments are often due to differences in their abundance of main S-containing ingredients, as residual sulfate and cysteine or methionine containing proteins. This is similar with animal tissues and products. Therefore, the sulfur isotope analysis of the bulk matter or of defined fractions of plant and animal samples is an ideal and reliable tool for food origin and authenticity proof and for archaeological and animal migration research.