Application of Direct Analysis in Real Time (Part 1) Rapid Analysis of Fatty Acids and Amino Acids in Food Using LCMS-2020

Importance of the Topic

Direct and high‐throughput analysis of food components is crucial for quality control and screening purposes. Fatty acids and amino acids in dried fish products are key indicators of nutritional value and processing effects. Conventional methods require time‐consuming extraction and derivatization steps. DART‐MS offers a rapid alternative by ionizing samples in ambient conditions, enabling immediate detection without pretreatment.

Objectives and Study Overview

This application note presents the direct characterization of free fatty acids and amino acids in two forms of katsuobushi (dried bonito): arabushi (pre‐mold) and hongarebushi (post‐mold). The aim was to evaluate the feasibility of DART coupled with a single quadrupole mass spectrometer for fast screening, to compare surface and internal sample regions, and to observe changes induced by the mold fermentation process.

Methodology and Instrumentation

A DART‐SVP ion source was mounted on a Shimadzu LCMS‐2020 single quadrupole mass spectrometer.

• DART heater temperature: 100–500 °C (optimized at 200 °C for fatty acids, 400 °C for amino acids)
• Mass range: m/z 50–1500 with rapid polarity switching (15 msec) and up to 15,000 u/sec scanning
• Nebulizing gas flow: 1.5 L/min; drying gas flow: 5.0 L/min
• DL temperature: 250 °C; block heater: 400 °C

Sample slices from surface and internal regions were directly held in the DART gas stream without any extraction or derivatization. Measurements took approximately 10 seconds per position.

Key Results and Discussion

• Fatty acids: Palmitic, oleic, stearic, EPA, DHA, and other free fatty acids were detected in negative ion mode. Characteristic fish‐derived PUFAs (EPA, DHA) appeared as ammonium adducts in positive mode; their signals were strongest on the hongarebushi surface.
• Amino acids and peptides: Histidine, carnosine, and anserine were observed in positive ion mode without derivatization. The histidine peak highlighted the contribution of migratory fish metabolites.
• Sample comparison: Hongarebushi surfaces exhibited the highest free fatty acid signals, suggesting that mold fermentation increases lipid hydrolysis. Arabushi showed lower levels, and internal regions had reduced signal intensities in both types.

Benefits and Practical Applications

• High‐throughput screening: Analysis time reduced from hours to seconds per sample without solvent use.
• Minimal sample preparation: Direct analysis of solid samples simplifies workflow for quality control and authenticity testing.
• Versatility: Applicable to various sample matrices (gases, liquids, solids) and capable of dual‐polarity detection.

Future Trends and Applications

• Quantitative method development combining DART‐MS with internal standards for routine food analysis.
• Integration with high‐resolution or tandem MS to improve structural elucidation and isomer differentiation.
• Automation and robotic sample handling to further increase throughput and reproducibility in industrial QA/QC.
• Extension to other fermented foods, complex matrices, and in‐line process monitoring.

Conclusion

The DART‐MS approach coupled with a fast single‐quadrupole MS demonstrates efficient, pretreatment‐free detection of free fatty acids and amino acids in katsuobushi. Mold fermentation notably enhances surface lipid hydrolysis, a phenomenon readily captured by this method. The streamlined workflow offers significant advantages for rapid food analysis and quality assessment.

Reference

Shun Wada et al. High throughput characterization of Katsuobushi using DART‐MS with high‐speed polarity switching (Poster No.ThP633), ASMS 2014, Baltimore.