Carbon isotopic characterization of cider CO sub(2) by isotope ratio mass spectrometry: a tool for quality and authenticity assessment

RATIONALE The cider market is an important sector of the food industry in certain regions. Adulteration of cider can happen in several ways: for example, by the addition of sugar, or of exogenous CO sub(2) to certain types of cider. Because such practices are not allowed by either Spanish legislation or the legislation of other countries, it is essential to study possible methods to detect these unauthorized practices. For this purpose a procedure was required to study the stable carbon isotopic composition of CO sub(2) in cider. METHODS A liquid sample of cider was transferred to a vial and CO sub(2) from the headspace of the vial was analyzed using a peripheral device interfaced to an isotope ratio mass spectrometer. Separation of the CO sub(2) from water and ethanol was achieved using a gas chromatography column located in the peripheral device. RESULTS The values for repeatability and reproducibility obtained indicated the robustness of the method, which is required for routine analysis. Ninety cider samples from various origins were analyzed, most of which showed a super(13)C content consistent with the declared origin. The [delta] super(13)C ranged from -24.80ppt to -20.89ppt for ciders with endogenous carbon dioxide (-22.74 plus or minus 0.79ppt) and -37.13ppt to -26.00ppt if industrial CO sub(2) was added. Several samples were also suspected of C4 sugar addition prior to the fermentation. CONCLUSIONS A fast, accurate and simple method for cider adulteration detection was developed. The addition of exogenous CO sub(2) as well as C4 sugar addition prior to fermentation could be detected. The method showed advantages over existing methods in term of simplicity (no sample preparation and very long-term stability of the sample), speed (less than 10min/sample) and precision ((r less than or equal to 0.32 and R less than or equal to 0.42). Copyright [copy 2012 John Wiley & Sons, Ltd.