Isotope ratios of bioelements for inferring beef origin and zebu feeding regime in Cameroon

The aim of the study was to deal with a lack of knowledge regarding the stable isotope composition of beef from zebu cattle reared in tropical Africa. Sixty beef carcasses belonging to the most popular zebu breeds (Goudali, White Fulani and Red Mbororo) were selected and sampled at the slaughterhouse of Yaounde. The carcass fat colour was visually evaluated on three-level qualitative scale (white, cream or yellow). The stable isotope ratios of five bio-elements - H, O, C, N and S - were analysed in protein and fat muscle fractions, together with the fatty acid composition of meat samples from Longissimus dorsi muscle. Zebu beef from Cameroon has a particular isotope profile, characterised by higher δ13C, δ2H and δ18O values than those reported in other areas of the world, as a consequence of the almost exclusive use of tropical C4 pasture grasses for cattle feeding and of the geographic and climatic gradient in the isotope composition of precipitatation water. Moreover, the isotopic composition of the fat fraction of muscle was significantly affected by the subcutaneous fat colour. Zebu with white subcutaneous fat (“white type”) showed a clear tendency to be more enriched in 2H isotopes and more depleted in 13C isotopes than the “yellow type” , while the “cream type” represented an intermediate condition. These trends correlated with fat composition: 2H enrichment and 13C depletion were significantly correlated with a high PUFA content, while 2H depletion and 13C enrichment were correlated with a high SFA content. It was argued that, as a consequence of better nutritional status, the “yellow types” had a more diluted phospholipid (PL) content and a higher proportion of neutral lipids (NL) in their fat in comparison with the “white types”, and thus a less negative δ13CFAT value, in agreement with the findings that PL fraction displays a more negative diet-tissue fractionation than NL fraction. Within Cameroon, multi-element analysis give promising results for tracing the regional origin of beef and some aspects of the cattle breeding system, such as the animal’s nutritional status.