GC-C-IRMS on single fatty acids and EA-IRMS on bulk lipid to study the fractionation processes in bovine organism and to detect differences in four matrices of Simmental cows fed on C3 and C4 diets

Fatty acids (FAs), carboxylic acids with a long aliphatic chain, detectable in both adipose tissue and muscle of animals, strongly contribute to different aspects of meat quality and are central to the nutritional value of this product [1]. Focusing of bovine meat, we must consider that the FAs may derive either from the animal diet only, as is the case with essential linoleic and linolenic acid, or from de novo endogenous synthesis, or both [2]. As for the biosynthetic pathway the FAs follow in cow organism, dietary FAs undergo substantial transformations into the digestive tract before depositing into the tissues. First, the hydrolyzation of complex lipids deriving from the diet, carried out by bacteria and protozoa in the rumen, produces long chain fatty acids (LCFAs) and other organic compounds [3]. Then, the free FAs released during hydrolysis are converted to saturated ones, primarily stearic and secondarily palmitic acid through biohydrogenation [3]. On exiting the rumen, the FAs flow into the duodenum, where the absorption takes place. Furthermore, the FAs reach the liver carried by the blood, whose flow, together with the FAs concentration, influences their supply to this organ [5]. In this work, two groups of multiparous cull cows fed according to two different dietary regimes (based on products deriving from plants characterized by either C3 or C4 photosynthetic cycle) were considered. The different paths C3 and C4 plants follow for CO2 fixations result in discriminating carbon isotopic ratios (δ13C). Therefore, the ability to distinguish between animals directly comes from the isotopic differences in the feeding regimes. Different cow compartments (rumen, duodenum, liver and meat) led to the diet-based discrimination of the animals. The presented results were obtained by analysing the δ13C of both the bulk lipidic extract through EA-IRMS and six FAs through GC-IRMS in each compartment. Furthermore, it is worth considering that several chemical reactions resulting in isotopic fractionation take place in the bovine organism. On this basis, the compound-specific analysis of the fatty acids in the different compartments of all cows gave the opportunity to compare the fractionation processes taking place in the bovine organism and to highlight differences depending on the dietary regime of the cows, whether C3- or C4- based