Underivatized Amino Acid Profiling in Yeast Fermentation Samples

Significance of the topic

Monitoring small-molecule composition of fermentation media is essential for understanding nutrient consumption, metabolic byproduct formation, and culture health during bioprocess development. Amino acids are key nutrients and intermediate metabolites; their accurate, reproducible measurement informs media optimization, feed strategies, and strain performance. Methods that avoid chemical derivatization shorten sample workflows and preserve analyte integrity, but they must maintain chromatographic performance and sensitivity for a wide dynamic range of concentrations.

Objectives and overview of the study

The application note demonstrates an LC/TOF-MS workflow for direct quantitation of underivatized amino acids in Saccharomyces cerevisiae fermentation media. Key aims were to: (1) preserve metal‑sensitive analytes using a biocompatible (iron‑free) LC flow path, (2) separate and quantify underivatized amino acids using HILIC chromatography, and (3) combine targeted quantitation with untargeted, high‑resolution full‑scan metabolite profiling to monitor fermentation dynamics over time.

Methodology

Sample collection and preparation:

• Organism and culture: Saccharomyces cerevisiae (ATCC 204508) grown at 30 °C in 20× diluted Y5000 yeast peptone dextrose broth.
• Time points: samples collected every 2 h from 0 to 12 h and at 24 h.
• Clarification: centrifugation at 5,000 × rcf for 5 min to remove cells; supernatant diluted 1:4 with 50:50 methanol:water, vortexed and centrifuged at 10,000 × rcf for 10 min.
• Final dilution: extracted supernatant diluted 20× into 70:20:10 acetonitrile:water:methanol prior to injection.
• Calibration: external standards (Agilent Amino Acid Analysis standard, supplemented with glutamine, asparagine, tryptophan) over 50–50,000 nM (n = 4) to span expected sample concentrations.

Chromatography and mass spectrometry (overview of key parameters):

• Column: Agilent Altura Poroshell 120 HILIC‑Z, 2.1 × 150 mm, 2.7 µm, operated at 30 °C.
• Mobile phases: 10 mM ammonium acetate, pH 9.0 (A: water; B: 90:10 acetonitrile:water).
• Flow: 0.25 mL/min; injection volume: 3 µL; total run time: 25 min; gradient from high organic (≈90% B) to increased aqueous to elute analytes, then re‑equilibration.
• MS: Agilent 6230C TOF LC/MS with Jet Stream source in negative polarity; m/z range 60–1,000 (high‑resolution accurate mass full scan); sheath gas temp 300 °C; capillary voltage 3,000 V; nebulizer 40 psi.
• Software: MassHunter Quantitative Analysis 12.1 for targeted calibration and quantitation; MassHunter Explorer 2.0 for untargeted feature extraction, PCA, and annotation using a custom PCDL of standards (accurate mass + retention time).

Main results and discussion

Chromatography and quantitative performance:

• HILIC separation retained and resolved underivatized amino acids, with most analytes eluting within the first 10 min. Baseline separation of isomers leucine and isoleucine was achieved, enabling accurate individual quantitation.
• Calibration curves showed excellent linearity (R2 > 0.998 for most amino acids) across a broad dynamic range (50–50,000 nM for several analytes), spanning roughly three orders of magnitude.
• Reproducibility: replicate injections produced relative standard deviations (RSDs) < 10% for peak areas; mass accuracy was maintained below 2 ppm.

Biochemical trends observed during fermentation:

• Targeted quantitation revealed distinct depletion patterns for specific amino acids—some compounds were rapidly consumed to support growth and protein synthesis, while others changed minimally over the 24‑hour period.
• Untargeted full‑scan data enabled detection of other metabolite classes: an increase in lactic acid signal was observed between 0 and 8 h, consistent with fermentation by‑product excretion, and hexose monosaccharide signals decreased over time as sugars were consumed.
• Multivariate analysis: PCA on untargeted features clustered samples according to fermentation time, demonstrating broad shifts in metabolite composition as the culture progressed.

Advantages of the biocompatible HILIC‑TOF workflow:

• Iron‑free, Ultra Inert flow path (Altura Poroshell + 1290 Infinity II/III bio LC) reduces metal–analyte interactions that can degrade peak shape or suppress signals for metal‑sensitive compounds.
• Negative‑mode TOF full scan provides simultaneous coverage of amino acids, organic acids, and carbohydrates in a single injection—supporting complementary targeted and discovery analyses and retrospective interrogation of data.

Used instrumentation

• Agilent 1290 Infinity II bio LC (methods compatible with 1290 Infinity III bio LC).
• Agilent Altura Poroshell 120 HILIC‑Z column, 2.1 × 150 mm, 2.7 µm (Ultra Inert hardware, iron‑free flow path).
• Agilent 6230C TOF LC/MS with Jet Stream ion source and VacShield technology.
• Agilent MassHunter Quantitative Analysis 12.1 and MassHunter Explorer 2.0 for targeted quantitation, untargeted feature extraction, PCA, and annotation; custom PCDL for amino acids.

Benefits and practical applications

• Elimination of derivatization simplifies sample preparation, reduces turnaround time, and preserves metabolite integrity while maintaining sensitivity and chromatographic resolution.
• Broad dynamic range and good reproducibility enable monitoring both low‑ and high‑abundance amino acids during fermentation without multiple methods.
• Combined targeted and untargeted data support process development tasks such as media optimization, feed strategy design, strain comparison, and early detection of metabolic shifts or by‑product accumulation.

Future trends and potential applications

• Integration with automated sample handling and high‑throughput workflows for real‑time or near real‑time bioprocess monitoring.
• Expansion to isotope‑labeling experiments to quantify fluxes and pathway activity during fermentation.
• Coupling high‑resolution MS with orthogonal separations (e.g., ion mobility) to increase chemical coverage and improve isomer discrimination for complex metabolites.
• Application to other bioprocess systems (mammalian or bacterial cultures) and to broader metabolome coverage by optimizing extraction and ionization strategies.
• Use of retrospective full‑scan datasets for discovery of emergent biomarkers or for regulatory/compliance investigations in QA/QC workflows.

Conclusion

This work demonstrates a robust HILIC‑LC/TOF‑MS approach for quantitative monitoring of underivatized amino acids in yeast fermentation media. The combination of an iron‑free, Ultra Inert flow path and high‑resolution TOF detection delivers accurate, reproducible quantitation across a wide dynamic range while enabling untargeted metabolomic profiling from the same run. The workflow supports actionable biochemical insights for fermentation process development and is adaptable to broader metabolomics applications.

References

1. Maicas S. The Role of Yeasts in Fermentation Processes. Microorganisms. 2020;8(8):1142.
2. Hsiao J, Chu T‑W, Kennedy A, Bivens A, Blackwell A. Analysis of Underivatized Amino Acids by LC/MS for Bioreactor Cell Culture Monitoring. Agilent Technologies application note 5991‑8816EN. 2018.
3. Hsiao J, Masigol M, Closser R, et al. Pushing the Boundaries of Chromatographic Separation with Inert HPLC Column Hardware. Agilent Technologies white paper 5994‑8618EN. 2025.