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

Significance of the Topic

Ensuring the authenticity and quality of food products is vital for consumer safety and industry standards. Biomarkers such as trigonelline, an alkaloid abundant in green coffee beans and quinoa, serve as indicators of freshness, origin and processing conditions. Rapid, sensitive and portable analytical approaches are required to monitor these compounds during production, storage and distribution.

Objectives and Study Overview

This work demonstrates a field-deployable method for quantifying trigonelline in aqueous samples using Surface-Enhanced Raman Spectroscopy (SERS). By combining a portable Raman spectrometer with gold nanotriangles functionalized with mercaptopropionic acid, the study aims to lower the detection limit, accelerate analysis and minimize sample requirements compared to conventional Raman measurements.

Methodology and Instrumentation

The experimental setup and procedures included:

• Portable Raman spectrometer: i-Raman Plus 785S equipped with a 785 nm laser, TE-cooled CCD detector; spectral range 150–2800 cm⁻¹; integration time 50 s; 10 scans; 10 mm cuvette.
• Nanoantenna synthesis: Gold nanotriangles modified with mercaptopropionic acid dispersed in water.
• Sample preparation: Aqueous trigonelline standards from 10 mM down to 0.5 mM mixed with gold nanotriangles at a 15:2 volume ratio.
• Data acquisition: Monitoring of the 1034 cm⁻¹ Raman band (pyridine ring breathing mode) within 1010–1045 cm⁻¹ for calibration.

Results and Discussion

Conventional Raman analysis of a 250 mM trigonelline solution revealed a strong 1034 cm⁻¹ signal. Comparing four replicate series across five concentrations showed that SERS with gold nanotriangles enhanced the signal‐to‐noise ratio markedly. Calibration curves derived from the SERS peak area exhibited linear response down to below 0.5 mM, outperforming standard Raman in sensitivity and detection limit. The gold nanoantenna geometry was optimized to maximize enhancement in the 700–800 nm emission region.

Benefits and Practical Applications

The described approach offers several advantages:

• Lower detection limits for trigonelline, enabling trace analysis in beverages and raw food materials.
• Reduced sample volume and rapid acquisition—suitable for on-site quality control.
• Portability of the spectrometer allows implementation in production lines, warehouses or point-of-sale environments.

Future Trends and Opportunities

Advancements may involve:

• Multiplexed SERS substrates for simultaneous monitoring of multiple biomarkers.
• Integration with smartphone-based readouts and cloud analytics for real-time decision support.
• Expansion to non-invasive packaging analysis using STRaman technology.
• Enhanced multivariate algorithms to distinguish complex sample matrices and adulterants.

Conclusion

The combination of portable Raman instrumentation with tailored gold nanotriangles provides a robust, sensitive and field-ready method for trigonelline quantification. This strategy promises to strengthen quality control in coffee, quinoa and other food sectors by delivering fast, reliable biomarker analysis outside the traditional laboratory setting.

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. Direccion de Gestion de la Investigacion (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. Direccion de Gestion de la Investigacion (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.