Drying and storage influence the formation of key aromatic constituents in Blue Fenugreek (Trigonella caerulea)

The dried herb of blue fenugreek is used as a spice in the alpine region for the preparation of traditional bread and cheese. After drying, the herb is stored for a period of six to twelve months. During this time, the herb is expected to undergo changes in the compositions of the major flavor- and odor-determining compounds. To identify eventual biochemical processes, we applied different growing (conventional and sterile) and drying (air- and freeze drying) conditions and subsequently conducted periodical analysis of key aroma constituents (α-keto acids and volatile compounds) by LC-MS and GC-MS. The amount of glyoxylic acid was drastically increased in the air-dried sample, while the freeze-dried sample showed significantly higher amounts of α-keto-glutaric acid and pyruvic acid, respectively. During storage, a decrease in sulfuric compounds and an increase in alkane aldehydes were observed when comparing conventional and sterile samples. However, this increase was even greater for monoterpenes (especially camphor and p-cymene), showing thrice as high amounts after storage. Interestingly, both compounds were only formed significantly during the storage under conventional conditions, indicating that their production is induced/caused by microbial organisms.