Thermal degradation pathways of rapeseed aliphatic glucosinolates and flavor characteristics of volatile products.

Glucosinolates are key sulfur-containing metabolites in rapeseed that contribute to the flavor of rapeseed oil. However, the volatile compounds and forming pathways remain unclear. This study investigated changes in rapeseed glucosinolates during thermal processing using HPLC. Aliphatic glucosinolates accounted for 90% of total glucosinolates, and their degradation proceeded extensively during heating. Volatile compounds, including two isothiocyanates, fourteen nitriles, and one indole were identified in the corresponding rapeseed oil via HS-SPME-GC/MS-O. Four major aliphatic glucosinolates were then examined in model thermal degradation systems (water, glycerol, pH = 5, 7 and 9). 3-butenyl glucosinolate generated volatile 3-butenyl isothiocyanate via a Lossen-like rearrangement. Hydrolysis of 4-methylsulfinylbutyl glucosinolate produced 4-(methylsulfinyl)butyl isothiocyanate. Pungent compounds, including 4-pentenenitrile, (Z,Z)-2,4-pentadienenitrile, and (E,E)-2,4-pentadienenitrile, originated from 3-butenyl glucosinolate and 2-hydroxy-3-butenyl glucosinolate. In addition, thermal decomposition of 4-(methylsulfinyl)butyl glucosinolate produced trace amounts of thioether compounds under alkaline conditions. This study provides a theoretical basis for targeted regulation of rapeseed oil flavor quality.