Analytical methods for authenticity testing of organically grown vegetables are urgently needed. Danish researchers have developed a novel assay for organic authentication based on stable isotope ratio analysis (SIRA) of oxygen in plant-derived sulphate. This method was compared with SIRA of bulk plant tissue and plant-derived nitrate to discriminate organic and conventionally grown potato, carrot, and cabbage from rigidly controlled long-term field trials and from a case study using retail potatoes. The results indicated that oxygen isotope ratios of sulphate from organic vegetables were significantly lower compared to their conventionally grown counterparts, and the values were directly linked to the fertilisation strategy. The classification power of sulphate isotope analysis was superior compared to known bulk tissue isotope markers and nitrate isotope values, and hence represents a promising new method for authentication of organic vegetables.
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