Stable carbon isotope ratio analysis (
SCIRA) was used to determine the authenticity of commercialAustralian orange juices. Thirty-five samples of Valencia (
13C values from -23.8 to -24.7 ppt)and eight samples of Navel juices (
13C values from -24.1 to -24.5 ppt) of known origin were usedto establish a decision level before analysis. No significant seasonal variations in
13C/
12C ratio wereobserved. Variations in combustion temperature in the method were also found to be insignificant.Keywords: Authenticity; adulteration; SCIRA; stable carbon isotope ratio; orange juice; Valencia;Navel