An authentication study of Vietnamese passion fruit juice using pulp, organic acids, and sugar-specific stable isotopes

This study employs stable isotope analysis to detect adulteration in passion fruit juice. By analyzing oxygen isotope ratios (δ¹⁸O) in juice water, genuine products can be differentiated from diluted samples, while carbon isotope ratios (δ¹³C) enable the identification of C4-derived sugars and acids not naturally present in juice. Totally 41 passion fruit samples were analyzed for stable isotope ratios (δ¹³C, δ¹⁵N, δ¹⁸O) of multiple juice components, including pulp, sugars, organic acids, and water. The δ¹³C values ranged from −23.2 to −30.45 ‰, with a maximum standard deviation of 0.9 ‰. Based on these results and a 99.7 % confidence level, component-specific authenticity limits and isotopic consistency criteria (Diff.max < 5 ‰), diff.(pulp-sugar) ≥ 0 ‰, diff.(pulp-acid) ≥ −1.0 ‰ and diff.(acid-sugar) ≥ −1.0 ‰ were established for authentic passion fruit juice, with fruit pulp serving as a reliable internal reference for detecting the addition of foreign sugars and acids. Compound-specific isotope analysis confirmed the effective detection of C4 sugar, HFCS, and citric acid adulteration at low levels, whereas C3-derived sugar adulteration was only conditionally detectable at higher addition levels. The δ¹⁸O values of juice water enabled the identification of undeclared dilution in NFC juice. Multivariate analysis of δ¹³C profiles further suggested patterns of geographical variability; however, these findings are considered exploratory due to limited sample size and partial overlap among regional groups. Overall, stable isotope analysis provides a robust tool for authenticating passion fruit juice and detecting adulteration.