Are Your Cornflakes Stale? Hexanal Formation in Grain Products

Significance of the Topic

The formation of hexanal in grain products is a key marker of lipid oxidation and shelf life degradation. Even at trace levels, hexanal imparts a green, grassy off-odor that can undermine consumer acceptance of cereal and other cereal-based foods. Developing reliable, sensitive analytical methods for monitoring hexanal is essential for quality control, product development, and ensuring consistent sensory profiles in the food industry.

Study Objectives and Overview

This study aimed to compare two headspace sampling techniques—static headspace and solid-phase microextraction (SPME)—for quantifying hexanal generated in corn flakes over a ten-week aging period. By tracking hexanal formation as cereal sits exposed to air, the investigation evaluates method sensitivity, precision, and chromatographic performance under optimized conditions.

Methodology

The experimental workflow involved:

• Sample Preparation: Commercial corn flakes were opened, dated, and stored at ambient conditions for intervals of fresh, 3 days, 2, 3, 6, and 10 weeks. Flakes were crushed to ~2–3 mm pieces for improved analyte recovery.
• Headspace Sampling:
• Static Headspace: 1 g sample in 20 mL vial, incubated at 120 °C for 20 min with agitation, 2 mL headspace withdrawal.
• SPME: Same vial format, incubated at 60 °C for 10 min with PDMS/DVB fiber exposed 5 min in headspace.
• Optimization: Temperature, incubation time, agitation speed, and extraction parameters were varied to maximize hexanal partitioning and reproducibility. Each condition was run in quintuplicate to assess relative standard deviation (RSD).

Used Instrumentation

• EST Analytical FLEX Autosampler configured for static headspace (2.5 mL syringe) and SPME (PDMS/DVB fiber).
• Agilent 7890 Gas Chromatograph equipped with Restek Rxi-5Sil MS column (30 m × 0.25 mm ID, 0.25 µm film).
• Agilent 5975 Mass Spectrometer, electron impact ionization, scan range m/z 35–265.
• Temperature Programs: Headspace run time ~12.5 min; SPME run time ~17 min; helium carrier gas at 0.8 mL/min.

Key Findings and Discussion

Hexanal area counts increased steadily with storage time for both methods. Static headspace counts rose from ~1.1 × 10⁶ (fresh) to ~1.1 × 10⁷ (10 weeks), while SPME signals increased from ~1.5 × 10⁵ to ~4.2 × 10⁶. Both techniques achieved RSD values below 10%, indicating good precision.
However, SPME yielded sharper, more defined hexanal peaks and lower baseline noise compared to broader, less resolved headspace signals. This enhanced chromatographic performance facilitates more accurate integration and quantitation, particularly at low concentrations.

Benefits and Practical Applications

• Rapid, solvent-free sampling ideal for routine monitoring of flavor compounds in cereals and other food matrices.
• Comparable precision for both methods, enabling flexible adoption based on existing instrumentation and throughput needs.
• SPME’s superior peak shape supports trace-level detection and improved quantitation of oxidation markers in quality control labs.

Future Trends and Opportunities

Advances in fiber coatings and high-throughput autosamplers will further enhance SPME sensitivity and selectivity for diverse volatile markers. Integration with two-dimensional GC and high-resolution MS can expand compound coverage and resolve coeluting species. Real-time ambient sampling techniques and portable SPME devices offer potential for on-site shelf-life assessment and dynamic monitoring in production lines.

Conclusion

This comparative study demonstrates that both static headspace and SPME effectively track hexanal formation in aging cereal, with similar precision. SPME’s distinct advantage in peak resolution and signal clarity makes it the preferred technique for sensitive, reliable flavor analysis in quality control and research settings.

References

• Jurek A. Solid Phase Micro Extraction of Flavor Compounds in Beer; Application Note. EST Analytical, Cincinnati, OH.