Is your juice truly organic? An isotopic approach for certifying organic grape juice

The sustainability and authenticity of grape juice production have gained increasing attention, particularly regarding the environmental impact and health benefits of organic practices. This study aimed to evaluate the isotopic composition of nitrogen (δ15N) and carbon (δ13C) in grape juices produced under organic and conventional farming systems, to determine whether these markers can differentiate production methods. A total of 36 samples (18 organic and 18 conventional) were analysed using elemental analysis and isotope ratio mass spectrometry. Results showed significantly higher δ15N values in organic grape juices (mean of 7.78 ‰), consistent with the use of organic fertilisers naturally enriched in 15N. In contrast, conventional juices had significantly lower δ15N values (mean of 1.24 ‰), reflecting the use of synthetic fertilisers. No significant differences in δ13C values were observed between systems, with all samples falling within the expected range for C3 plants, suggesting that carbon isotope ratios are more influenced by photosynthetic pathway and environment factors than by farming practices. These findings confirm that δ15N analysis is a reliable tool for distinguishing organic from conventional grape juices. This approach contributes to food authentication and supports sustainable agriculture verification.