Characterization of key aroma compounds in microgreens and mature plants of hydroponic fennel (Foeniculum vulgare Mill.)

Abstract

Fennel is a popular culinary herb known for its unique flavor. In this study, we identified key aroma-active compounds in fresh fennel (Foeniculum vulgare Mill.) and its microgreens. Fennel was cultivated hydroponically with soilless substrates. Upon harvesting, samples were ground with liquid nitrogen, and headspace solid phase microextraction (SPME) gas chromatography-mass-spectrometry-olfactometry (GC-MS-O) was used for volatile analysis. Thirty-two and 28 key aroma-active compounds were identified in fennel microgreens and mature leaves, respectively. Phenylpropenes, especially (E)-anethole, were the predominant aroma-active compound in all samples (36.3-83.4 %). Quantitation results showed that fennel microgreens contained a significantly higher amount of monoterpenes, showing an 81.4-98.1 % increase when compared to mature fennel. Principal component analysis (PCA) of identified volatiles indicated a distinctive difference in the overall aroma profile between microgreens and mature leaf. The changes in aroma contents over different growth stages revealed the underlying volatile biosynthesis discrepancy. This study provided baseline information for understanding the aroma evolution from microgreen to mature fennel herbs.

Keywords: Aroma characterization; Gas chromatography-mass-spectrometry-olfactometry (GC-MS-O); Leaf fennel; Monoterpenes; Phenylpropenes; Secondary metabolites.