HPLC/EA-IRMS: Identifying adulterated coconut juice using isotope fingerprints

Significance of the Topic

The demand for pure coconut water has risen due to its perceived health benefits and low carbohydrate content. Ensuring authenticity is essential to protect consumers and to comply with regulations on juice labeling.

Study Objectives and Overview

This summary is based on Psomiadis et al 2018, focusing on the use of carbon isotope fingerprinting to detect sugar adulteration in both authentic and retail coconut water samples. The goal was to compare isotopic signatures of pulp, bulk sugars, and individual sugars (sucrose, glucose, fructose).

Methodology

Samples of authentic coconut pulp and juice were prepared following ENV12140. Bulk sugars were precipitated as calcium salts, and individual sugars were separated for analysis. δ13C values were measured by Elemental Analysis–Isotope Ratio Mass Spectrometry (EA-IRMS) and by HPLC coupled to EA-IRMS, using internal acetanilide and sorghum standards calibrated against VPDB.

Used Instrumentation

• Thermo Scientific EA IsoLink IRMS system
• Thermo Scientific LC IsoLink IRMS system
• High-performance liquid chromatograph coupled to IRMS
• Centrifuge, vacuum dryer, filtration apparatus

Key Results and Discussion

Authentic coconut samples exhibited δ13C values within the typical C3 plant range (~−33‰ to −22‰). Bulk sugar analysis flagged 21% of commercial samples as adulterated. When examining individual sugars, the method identified 38% adulteration and achieved detection limits below 10% added C4 sugar, demonstrating superior sensitivity.

Benefits and Practical Applications

This targeted isotope analysis enhances the detection of C4 sugar adulteration, supports regulatory compliance for juice labeling, and provides a reliable quality control tool for laboratories in the food and beverage industry.

Future Trends and Opportunities

Advancements may include automation of sample preparation, expansion to multielement isotopic profiling, and application of similar fingerprinting strategies to other beverages, further strengthening authenticity testing and fraud prevention.

Conclusion

Carbon isotope fingerprinting of individual sugars offers a powerful and sensitive approach for verifying coconut water authenticity, outperforming bulk sugar analysis and enabling the detection of low-level adulteration.

References

• Psomiadis D Zisi N Koger C Horvath B Bodiselitsch B 2018 J Food Sci Technol 55 2994
• Farquhar GD Ehleringer JR Hubick KT 1989 Annu Rev Plant Physiol Plant Mol Biol 40 503 537
• OLeary M 1988 Bioscience 38 328 336
• AIJN Provisional Reference Guideline for Coconut Water and Juice 6.27 2017 Brussels Belgium