Underivatized Amino Acid Profiling in Fermentation Samples with Novel High-Resolution Mass Spectrometry Platform with Bio-Compatible Column and LC

Significance of the topic

Monitoring amino acid dynamics during microbial fermentation provides direct insight into nutrient uptake, metabolic state, and product formation. Reliable, high-throughput assays that quantify underivatized amino acids in complex fermentation matrices support process development, quality control and mechanistic studies in food and biotech industries. Eliminating derivatization simplifies workflows, reduces artefacts, and improves compatibility with online and high-throughput sampling strategies.

Objectives and overview

The study evaluates a workflow for quantifying underivatized amino acids in Saccharomyces cerevisiae fermentation supernatant using a bio‑inert HILIC column and a novel high‑resolution time‑of‑flight mass spectrometer. Key aims were to demonstrate chromatographic separation of isomeric amino acids, establish wide dynamic range calibration, achieve high mass accuracy, and apply the method to time‑course monitoring of amino acid depletion and fermentation byproducts.

Methodology

Sample preparation and fermentation sampling:

• Saccharomyces cerevisiae (ATCC 204508) grown in dilute Yeast Peptone Dextrose at 30 °C.
• Discrete sampling every 2 hours from 0–12 h and an additional 24 h point; cells removed by 5,000 x g centrifugation and supernatant collected.
• For amino acid extraction the supernatant was diluted 1:4 with 50% methanol:water and centrifuged; analytical injection samples were prepared by 20× dilution into 70:20:10 ACN:H2O:MeOH.
• 3 µL injection volume was used for LC/TOF analysis.

Chromatography and mobile phase:

• HILIC separation on an Agilent Altura Poroshell HILIC‑Z column (2.1 × 150 mm, 2.7 µm) at 30 °C with autosampler at 4 °C.
• Mobile phases: 10 mM ammonium acetate pH 9.0 (A) and 10 mM ammonium acetate pH 9.0 in 90:10 ACN:H2O (B).
• Flow 0.25 mL/min, 25 min total runtime with a gradient switching between high organic and higher aqueous to elute polar amino acids.

Mass spectrometry and quantitation strategies:

• Negative electrospray ionization with m/z range 60–1000; instrument parameters optimized for negative mode detection.
• Calibration curves produced from commercial amino acid standards over 50–50,000 nM range; retention time library constructed for identification in matrix.
• Quantitation and data review performed in MassHunter Quant; untargeted feature analysis and PCA performed in MassHunter Explorer.

Instrumentation used

• Agilent 1290 Infinity II Bio LC (bio‑compatible LC platform)
• Agilent Altura Poroshell HILIC‑Z column, 2.1 × 150 mm, 2.7 µm (bio‑inert column hardware)
• Agilent 6230C Time‑of‑Flight (TOF) mass spectrometer

Main results and discussion

Chromatography and reproducibility:

• HILIC separation provided baseline or near‑baseline resolution for many amino acids; isomeric separation of leucine and isoleucine was achieved and shown reproducible across injections.
• Injection‑to‑injection reproducibility for standards was excellent, supporting robust retention behavior on the bio‑inert Altura hardware.

Quantitative performance:

• Calibration curves demonstrated broad dynamic ranges for individual amino acids (typical ranges from 50 to 50,000 nM), with many analytes quantified over three orders of magnitude.
• Linearity was high (R2 values ≈ 0.998–0.999) and intra‑method precision was acceptable (RSDs < 10% reported for standards).
• Measured mass accuracy was better than 2 ppm for the evaluated amino acids, supporting confident elemental assignment and peak identity confirmation.

Application to fermentation time course:

• Quantitation of amino acids in the fermentation supernatant showed differential depletion patterns: several branched and aromatic amino acids (leucine, isoleucine, valine, phenylalanine, tryptophan) displayed significant decrease over the growth period while other amino acids showed distinct uptake kinetics.
• Principal component analysis of untargeted features captured global metabolomic changes over time, indicating the method can monitor broader metabolic shifts beyond targeted amino acids.

Simultaneous monitoring of fermentation byproducts:

• The high pH mobile phase and negative ion mode permitted concurrent detection of deprotonated amino acids and negatively charged organic acids (e.g., lactic acid) as well as tracking hexose depletion, enabling a more integrated view of carbon flux and fermentation status.

Method strengths and limitations:

• Strengths include avoidance of derivatization, high dynamic range, good mass accuracy, and bio‑inert hardware that minimizes adsorption of polar analytes.
• Limitations to consider are matrix effects inherent to complex fermentation broths (mitigated here by dilution and chromatographic separation) and potential coelution of some isobaric species that may require MS/MS confirmation in more complex samples.

Benefits and practical applications

• Routine monitoring of fermentation performance and nutrient depletion in food and beverage production, brewing and bioprocess development.
• Quality control applications where quick, derivatization‑free workflows reduce sample handling and turnaround time.
• Use in metabolic engineering and systems biology to correlate extracellular amino acid dynamics with intracellular pathways and phenotype.
• Capability to simultaneously monitor organic acids and sugars simplifies assay consolidation and reduces analytical overhead.

Future trends and potential applications

• Integration with online or at‑line sampling and automation for real‑time process monitoring and control in manufacturing environments.
• Combining this LC/HRMS approach with targeted stable isotope dilution methods to further improve absolute quantitation and correct for matrix suppression.
• Expansion to broader metabolomics panels and multi‑omics workflows, including MS/MS libraries for unequivocal identification of coeluting or isobaric compounds.
• Further improvements in column chemistries and hardware inertness to reduce adsorption of highly polar metabolites and extend applicability to other bioprocess matrices (mammalian or bacterial cultures).

Conclusions

The presented workflow using a bio‑inert Altura HILIC column coupled to the Agilent 6230C TOF provides robust, derivatization‑free quantitation of underivatized amino acids in yeast fermentation supernatant. The method exhibits high chromatographic reproducibility, excellent mass accuracy (<2 ppm), wide dynamic range with strong linearity (R2 ≈ 0.998–0.999) and practical sensitivity for monitoring nutrient depletion and fermentation byproducts. This approach is well suited for routine fermentation monitoring, process development and applications requiring integrated measurement of amino acids, organic acids and sugars without complex sample derivatization.

References

1. Maicas S. The Role of Yeasts in Fermentation Processes. Microorganisms. 2020;8(8):1142.
2. Hsiao J. et al. Pushing the Boundaries of Chromatographic Separation with Inert HPLC Column Hardware. Agilent White Paper 5994‑8618EN. 2025.
3. Hsiao J. et al. Analysis of Underivatized Amino Acids by LC/MS for Bioreactor Cell Culture Monitoring. Agilent Application Note 5991‑8816EN. 2018.