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Determination of the mixing extent of sugar from C4 plants in juice using the isotopic signature of carbon (δ13C) in sugar

The objective of this study was to apply a method for estimating the mixing extent of C4 sugar in juice (apple) based on the fingerprinting of carbon stable isotope (δ13C). The values of δ13C in sugar separated from fresh apples, pure apple juices as well as sugar produced from C4 plants (plants conduct C4 cycle photo-synthesis, in this case, it was sugar canes) were analysed on an isotope ratio mass spectrometer equipped with an elemental analyzer (EA IRMS). The results showed that the δ13C in sugar separated from fresh apples was in the range of -27.00 to -24.00‰ with an average of -25.47‰ (n=6) vs. VPDB standard (Vienna Pee Dee Belemnite). Meanwhile, the δ13C in sugar cane products ranged from -13.00 to -11.00‰, with an average of -12,47‰ vs. VPDB. Based on the isotope signature of carbon (δ13C) and the two end-members mixing model, the extent of mixing C4 sugar in apple juice available on the market could be estimated precisely. It was found one out of 9 apple juice samples available in the Hanoi markets to have a high content of C4 sugar mixed in the product, it was up to 96% instead of 5% as proclaimed on the label. The developed method seems to be of high accuracy so it was advisable to wider its application in the evaluation of the quality of juices available at the markets in Vietnam to ensure the right of the consumers.