Specific natural isotope profile studied by isotope ratio mass spectrometry (SNIP-IRMS):: 13C/12C ratios of fructose, glucose, and sucrose for improved detection of sugar addition to pineapple juices and concentrates

The delta(13)C values of fructose, glucose, and sucrose have been determined in authentic pineapple juices. The sugar fraction is separated from the organic acids by an anionic exchange process. Then the individual components (fructose, glucose, and sucrose) are isolated on a preparative HPLC device using a NH2-type column. It is demonstrated that no significant isotope fractionation occurs when close to 100% of material is recovered and when the hydrolysis of sucrose is avoided. The control of the recovery rates and of the sucrose hydrolysis rate after purification is recommended for a reliable interpretation of the results. Correlations between the delta(13)C values of fructose (delta(13)Cf), glucose (delta(13)Cg), and sucrose (delta(13)Csu) can be characterized by systematic differences between these values. For the set of measurements on authentic pineapple juices and concentrates, the mean and the standard deviation of the differences are delta(13)Cf - delta(13)Cg = -0.6 +/- 0.6 parts per thousand, delta(13)Cf - delta(13)Csu = -1.3 +/- 0.6 parts per thousand, and delta(13)Cf - delta(13)Csu = -0.7 +/- 0.5 parts per thousand. The determinations of the C-13 content of fructose, glucose, and sucrose enable a refinement of the detection of added sugars in fruit juices, re-enforcing the SNIP-IRMS method.