Not from concentrate (NFC) juice has better flavour and demands a higher price than reconstituted juice, and hence is more vulnerable to adulteration with sugar and water. This study investigates the use carbon and oxygen stable isotope ratios (δ13C and δ18O values) of the bulk juice and different juice components from 21 fruit and vegetable juicesto determine whether water and/or sugar has been added. Using juice pulp as an internal standard, δ13C values can qualitatively and quantitatively indicate the presence of C4 plant sugars in NFC juice, and can reliably detect added C4 plant sugars above 7 %. Determination of δ13C values of different juice sugars (sucrose, glucose and fructose) and carbon content can qualitatively infer C3 plant sugar addition to NFC juices. δ18O values of the pulp extracted from juice had a good linear relationship with the juice water δ18O values (R2 > 0.90). Also, comparison of δ18O values of extraneous water, pulp and filtered juice can also determine water addition to NFC juices. 

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