Aroma-impact compounds in dried spice as a quality index using solid phase microextraction with olfactometry and comprehensive two-dimensional gas chromatography

A systematic experimental procedure is used to identify the aroma-impact compounds, leading to a shelf quality index based on head space solid-phase microextraction. Dried (ground) fennel seeds, having shelf life of 6 months (0.5Y) and 5 years (5Y), were used as a spice model for assessment of comparative aroma quality. Aroma-impact odorants were analysed by GC-olfactometry (GC-O) in parallel with comprehensive two-dimensional GC-flame ionisation detection (GC×GC-FID) using a polar/non-polar phase combination for the GC×GC column set. Tentative identification of aroma-impact odorants involved correlating data from the GC-O/FID system with GC×GC-time-of-flight mass spectrometry analysis by means of retention indices. Major compounds responsible for aroma perception were limonene, 1,8-cineole, terpinen-4-ol, estragole and trans-anethole, and showed an average decrease of 30-50% NIF from 0.5Y to 5Y. Monoterpenes which represent 'freshness', e.g. β-pinene and β-myrcene, exhibited identifiable aroma-impact only for the 0.5Y product. Sesquiterpenes and sesquiterpene oxides are suggested as an aging index, being present in increased amounts in 5Y. p-Anisaldehyde odour intensity for both samples remained the same (aroma perception sweet creamy, floral odour and Chinese seasoning powder).