MEASUREMENT OF C-13 C-12 RATIOS OF SUGARS, MALIC-ACID, AND CITRIC-ACID AS AUTHENTICITY PROBES OF CITRUS JUICES AND CONCENTRATES/

The carbon-13 content of sugars, malic acid, and citric acid has been determined in authentic orange, lemon, and tangerine juices. After a c leanup step, sugars and organic acids were separated from each other b y an anion-exchange process, and pure malic and citric acids were isol ated by preparative reversed-phase liquid chromatography, This method has been applied to the stable isotope analysis of citrus juice sample s of different botanical and geographical origins and of different yea rs. Correlations between the carbon isotope ratios of all metabolites have been found, and typical ranges for the differences in delta(13)C values between them have been defined for each fruit. These data provi de new tools for detecting adulterations that cannot be detected by th e conventional carbon-13 method with the whole juice.