Comparison between isotope ratio mass spectrometry (IRMS) and cavity ring-down spectroscopy (CRDS) for analysing the carbon isotope ratio and detection of adulteration in coconut water

This study investigated the carbon isotope ratio (¹³C/¹²C, δ¹³C in unit of parts per thousand or per mill, ‰) of different coconut water samples using elemental analysis isotope ratio mass spectrometry (EA-IRMS) and combustion module cavity ring-down spectroscopy (CM-CRDS). Natural coconut water from young coconuts from 12 provinces in Thailand (n = 94), adulterated coconut water containing three sweeteners (sucrose, glucose and fructose) at different concentrations and eight brands of commercial coconut water were analysed. The δ¹³C of all samples were not significantly different (P > 0.05) between the EA-IRMS and CM-CRDS analyses. The natural coconut water (C3 plant) had δ¹³C ranging from −21.58‰ to −27.79‰ (mean −24.64 ± 0.91‰). Three sweeteners (C4 plant) contained δ¹³C between −11.46‰ to −13.16‰. The use of δ¹³C determination can detect adulteration of a singular extraneous sweetener (either glucose or sucrose) down to a level of 2% of adulteration. For the detected δ¹³C values of commercial products labelled as ‘no added sugar’, about 50% of products were adulterated. This study demonstrates that CM-CRDS can be used as an alternative analytical platform to EA-IRMS for detecting adulterated products, especially coconut water.