Thermally Induced Generation of Desirable Aroma-Active Compounds from the Glucosinolate Sinigrin

Glucosinolates are the most abundant secondary sulfur-containing plant metabolites in the plant family of Brassicaceae. These phytochemicals are well-known for their enzymatic degradation induced by the enzyme myrosinase, resulting in pungent odor impressions derived from their respective degradation products. However, up to now, only little attention has been paid to non-enzymatic thermal degradation and the release of additional aroma-active compounds. Thermal treatment is particularly important in the processing of Brassica vegetables, and thereby, glucosinolates as precursors can act as a natural source of odorants. Application of gas chromatography-olfactometry to the volatile fractions obtained after heat treatment of sinigrin (2-propenyl glucosinolate) in different matrices (phosphate buffer at a pH value of 5, 7, or 9, silicon oil, silica gel (7% water), sea sand, and glycerol) showed a high potential to generate aroma-active compounds, mainly revealing onion- and garlic-like odor impressions deriving from sulfur-containing odorants. A clear dependency of the formation of desired aroma-active compounds upon the respective matrix was found, indicating the need of detailed investigations to obtain knowledge for the best use of glucosinolates as a source of natural aroma compositions. For example, the distillate obtained from sinigrin heat-processed in buffer solution at pH 7 led to the identification of 17 odorants.