Alpha-tocopherol stereoisomer analysis as discriminant method for distinguishing Iberian pig feed intake during the fattening phase

•We categorise α-stereoisomers in fat from pigs according to their feeding.•Analysis of α-tocopherol stereoisomers is a potent tool to assure quality.•A 90% success rate can be achieved in classification of Iberian pig samples.•This method allows the differentiation of pigs fed with natural resources.•A lower proportion of RRR-stereoisomer is found in pigs receiving a mixed diet. The use of stereoisomers of α-tocopherol to correctly classify Iberian pig fat samples according to their feeding system was investigated. Samples were obtained over two different seasons in controlled farms from the four categories of pigs described in the Industry Quality Policy (FREE-RANGE: pigs fed exclusively under free-range conditions; FREE-FEED: pigs fed free-range and supplemented with feed; FEED-OUT: pigs fed outdoors with access to grass and a mixed diet; and FEED: pigs fed exclusively a mixed diet). A higher presence of RRR-stereoisomer indicated a greater consumption of the natural form of tocopherol provided by acorns or grass, whereas a higher proportion of S forms were related to a higher mixed diet intake. Validation results showed 90% success in fat sample classification. Analysis of the RRR-stereoisomer together with γ- and α-tocopherol determination can be considered as a potent tool for distinguishing fat from pigs fed under free-range conditions or exclusively with acorns and grass from those receiving a supplemented diet at any time of their fattening phase.