Rapid quantification of isovaleraldehyde in sake by HPLC with post-column fluorescent derivatisation

Why was the work done: Elevated levels of isovaleraldehyde (3-methylbutanal) in sake gives rise to an unfavourable aroma of ‘mureka’ or ‘stuffy smell’. The concentration of isovaleraldehyde is typically higher in unpasteurised than pasteurised sake. Controlling the concentration of isovaleraldehyde in unpasteurised sake remains a major challenge for quality control. As existing methods for the quantification of isovaleraldehyde in sake require specialised sample preparation, there is a need for a simple and precise method. How was the work done: High-performance liquid chromatography with fluorescence detection and post-column derivatisation (HPLC-PCD-FLD) for determining the isovaleraldehyde content in sake has been developed with optimisation of the separation of peaks and derivatisation of aldehyde compounds. The new method was compared with the established method of headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). What are the main findings: The limit of quantification of the new method was 87 µg/L, and accordingly, the HPLC-PCD-FLD method could determine the concentration of isovaleraldehyde in sake below the reported threshold level. The precision of the HPLC-PCD-FLD method for the analysis of sake containing isovaleraldehyde (> threshold level) either matched or was superior to the HS-SPME-GC-MS method. Why is the work important: The new approach requires only particle removal for sample preparation, with an rapid analysis time (<1 h per sample), and requires a smaller sample volume (≈ 100 µL) than the alternative method (10 mL). These improvements contribute to a simpler and more efficient workflow for routine analysis of isovaleraldehyde in the quality control of sake.