Changes in stable isotope ratios in PDO cheese related to the area of production and green forage availability. The case study of Pecorino Siciliano.

RATIONALE: No study has investigated the variations in stable isotope ratios (SIRs) of bioelements within a Protected Designations of Origin (PDO) cheese and few studies have focused on the dietary background of animals. For traceability purposes, it is important to know how and whether these issues affect SIRs in a PDO cheese.

METHODS: Thirty-six Pecorino Siciliano cheese samples were collected in three east-Sicilian areas in seasons in which green herbage was present or absent in the diet of the animals. The determination of C, N and S SIRs was performed using an isotope ratio mass spectrometer coupled with an elemental analyser. The H and O SIRs were measured using an isotope ratio mass spectrometer equipped with a thermal conversion elemental analyser pyrolysis unit.

RESULTS: The C, N, H, O and S SIRs measured in defatted cheeses were subjected to a multivariate stepwise discriminant analysis to verify if cheeses could be distinguished based on their geographical origin and on the animals' feeding regimen. Sulfur and nitrogen SIRs allowed the best discrimination among the three areas (97.2% correct classification of the cheeses). The discrimination of the feeding system, to check the presence or not of fresh forage in the diet of the animals, correctly classified 86.1% of the cheeses. The C and O SIRs were the most effective parameters.

CONCLUSIONS: This study demonstrates that the variability in C, H, O, N and S SIRs can allow discrimination between cheeses produced in a narrow geographical region within a PDO area. This may lead to the search for new tools in authentication studies such as the creation of specific isoscapes. Moreover, this study confirms that SIR determination can also discriminate cheeses obtained from animals fed in stalls from those produced when animals have access to green forage, with benefit in terms of environmental impact, animal welfare and product quality. Copyright © 2017 John Wiley & Sons, Ltd.