Fast and Selective Detection of Trigonelline, a Coffee Quality Marker, Using a Portable Raman Spectrometer

Importance of the topic

Ensuring the authenticity and quality of food commodities such as coffee and quinoa has become critical for producers and regulators. Rapid and sensitive identification of key biomarkers can reveal processing history, detect adulteration and support consistent product standards. Surface-Enhanced Raman Spectroscopy (SERS), combining the molecular specificity of Raman scattering with signal amplification by metallic nanostructures, offers a field-deployable approach to monitor important alkaloids like trigonelline under real-world conditions.

Study objectives and overview

This work presents a portable SERS-based method to quantify trigonelline, an alkaloid linked to coffee quality and aroma formation. Using a handheld Raman spectrometer and gold nanotriangles functionalized with mercaptopropionic acid, the authors aim to lower detection limits, accelerate analysis and reduce sample requirements compared to conventional Raman. Calibration over a biologically relevant range assesses the technique’s suitability for routine quality control in the food industry.

Methodology and Used instrumentation

The analytical workflow involves mixing aqueous trigonelline standards (0.5–10.0 mM) with modified gold nanotriangles (ratio trigonelline:AuNTs = 15:2) and recording SERS spectra with a portable 785 nm Raman spectrometer. Key instrument parameters:

• Spectrometer: i-Raman Plus 785S portable system
• Laser excitation: 785 nm, 50 s integration, 10 accumulations
• Raman shift range: 150–2800 cm⁻¹
• Sampling: 10 mm pathlength liquid cuvette
• Enhancement substrate: gold nanotriangles modified via mercaptopropionic acid

Main results and discussion

Conventional Raman analysis of a 250 mM trigonelline solution reveals a strong band at 1034 cm⁻¹, corresponding to the pyridine ring breathing mode. Under identical conditions, SERS measurements of diluted samples exhibit marked signal enhancement and improved signal-to-noise. Calibration plots based on the 1034 cm⁻¹ peak area (integrated over 1010–1045 cm⁻¹) demonstrate linear response down to 0.5 mM, with reliable detection below this threshold. Comparison of spectra with and without gold nanotriangles highlights a clear gain in sensitivity, validating the benefit of nanoparticle-assisted amplification.

Benefits and practical applications

The portable SERS approach delivers several advantages:

• Lower detection limits vs. standard Raman, enabling measurement of trace biomarker levels
• Reduced sample volume and minimal preparation requirements
• Rapid analysis times compatible with on-site quality control
• Potential for non-destructive testing and integration into production lines

These attributes make it a promising tool for coffee roasters, quinoa producers and regulatory bodies to verify product integrity and processing conditions.

Future trends and potential applications

Emerging directions include:

• Development of nanoparticle substrates optimized for other food markers and complex matrices
• Integration with automated sampling heads and multivariate software for real-time decision support
• Application through opaque packaging using transmission SERS techniques
• Field deployment in agricultural settings for harvest and post-harvest monitoring

Combining SERS with portable spectrometers and advanced data analytics promises broader adoption in food safety and quality assurance.

Conclusion

This study demonstrates a straightforward SERS method, employing a handheld 785 nm Raman spectrometer and mercaptopropionic acid-modified gold nanotriangles, for quantifying trigonelline at sub-millimolar concentrations. The enhanced sensitivity, coupled with low sample demand and portability, highlights its potential as a routine analytical protocol for food quality control.

References

• Galarreta B.C., Hernandez Y., Saldana Ramos A. Sintesis y aplicacion de nanotriangulos de oro en el desarrollo de un metodo de cuantificacion de un potencial alcaloide terapeutico: la trigonelina. DGI-2016-352, PUCP.
• Galarreta B.C., Maruenda H. Espectroscopia vibracional y de resonancia magnetica nuclear en el control de calidad de cafe organico peruano y cafe instantaneo. DGI-2014-078, PUCP.
• Aroca R. Surface-enhanced vibrational spectroscopy. John Wiley & Sons, 2016.
• Jaworska A., Malek K., Marzec K.M., Baranska M. Nicotinamide and trigonelline studied with surface-enhanced FT-Raman spectroscopy. Vibrational Spectroscopy. 2012, 63:469–476.