Using Raman Microscopy to Detect Counterfeit Coconut Water

Recently, coconut water has seen an increase in popularity and the market is very lucrative. Per head, London, England, is the biggest consumer of coconut water in the world. In the United Kingdom alone there are over 40 brands of coconut water, and a liter can cost as much as £4.

Detecting Counterfeit Coconut Water

The majority of the coconut water supplied to the West comes from only five countries and this increase in popularity has resulted in an imbalance between supply and demand. This has led to criminal activity in the supply chain. As a result, scientists at the University of Manchester are studying the adulteration of coconut water using a Renishaw inVia™ confocal Raman microscope.

In 2017, 400 tonnes of coconut water were seized at the port of Felixstowe, England, by a national food-crime investigation. Subsequent testing revealed that of the twelve imported brands, seven had been adulterated.

The group that is conducting the research into fake coconut water is led by Prof. Roy Goodacre, from the Manchester Institute of Biotechnology. Mr Paul Richardson, his research student, used a Renishaw inVia Raman microscope to detect and quantify the adulteration of fresh coconut water stretched with water-sugar mixes.

Raman Spectroscopy

One of the main challenges that the study faced was to mimic typical adulteration of fresh coconut water, with a sugar/water mix used to maintain a consistent sweetness. They were able to detect adulteration with three different sugar solutions using the inVia Raman microscope and chemometrics. This means that, once optimized, Raman spectroscopy could be used as a reliable and fast screening method for detecting the stretching of coconut water, even if masked with very low sugar levels.

The group was asked why Raman spectroscopy was chosen for this research project and Mr Richardson said, “It is a fast and relatively inexpensive analytical method with the potential to be highly portable. Furthermore, it differs from the methods currently in place (SNIF-NMR* and IRMS**) in that it requires no sample preparation, allowing it to potentially be used as an effective screening method at points of entry.”

Mr Richardson continued, “The inVia system is a powerful Raman microscope which, with appropriate training, can allow the user to easily test and use a multitude of different settings including laser strength, acquisition parameters, and grating.  The ability to easily test different parameters and optimize our methods gave us more confidence in the detection capabilities of our models. Furthermore, the machine’s sensitivity allowed us to provide stronger evidence for our models.”

“My favourite aspect of the inVia microscope was the ability to automate sampling. As my work involved sampling multiple sets of 21 samples, I could simply prepare them, load them up on a 96-well plate, and run several hours of analysis overnight. Given that I had limited time for research, this allowed me to obtain more high-quality results, as I never had to compromise between quality and quantity. Along with those highlighted above, a great advantage of the inVia microscope, compared to other spectrometers I have used, is the small volume required for analysis. While low stock was never an issue for me, working with volumes under 1 ml made my sample sets far easier to generate and keep track of.” Added Mr Richardson.

Conclusion

Mr Richardson summarized how the inVia microscope was used for this research, “It is a great tool for research. Along with being a powerful spectrometer with microscopy capabilities, it has a multitude of useful features that simplify research. The ability to modify various parameters allows for diverse research to be performed on the same machine, and the small volumes requires make it ideal for biological research. Finally, the capacity for automation allows for far greater efficiency in data gathering.”

Paul Richardson from the Manchester Institute of Biotechnology

Paul Richardson from the Manchester Institute of Biotechnology

A paper on this work has been recently published by Mr Richardson and his colleagues: Paul I.C. Richardson, Howbeer Muhamadali, David I. Ellis, Royston Goodacre Rapid quantification of the adulteration of fresh coconut water by dilution and sugars using Raman spectroscopy and chemometrics, Food Chemistry, Vol 272, 2019, Pages 157-164, ISSN 0308-8146, https://doi.org/10.1016/j.foodchem.2018.08.038

References

*SNIF-NMR – specific natural isotope fractionation-nuclear magnetic resonance

**IRMS – isotope ratio mass spectrometry

This information has been sourced, reviewed and adapted from materials provided by Renishaw plc - Spectroscopy.

For more information on this source, please visit Renishaw plc - Spectroscopy.

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