Thermal stability of stigmasterol and β-sitosterol glucosides in fresh-cut bitter melon fruit

Charantin in M. charantia fruit comprises stigmasterol glucoside (STG) and β-sitosterol glucoside (BSG). Despite numerous studies on charantin quantification and health beneficial bioactivity, thermal stability of two components remains unclear. This study investigated the thermal stability of BSG and STG in the fruit growth stages (S1-S5). Freeze-dried fruit contained approximately twice higher BSG than STG, with the content tending to decrease during fruit maturation. A dramatic decrease in content was observed between S2 and S3, with a reduction of 70 % for BSG and 75 % for STG. In thermal processing, BSG significantly degraded above 30 °C treatments, while STG remained stable. It was found that the thresholds of thermal stability were approximately 10 °C for BSG and 30 °C for STG. Therefore, minimal thermal processing or freeze-drying is recommended for preserving charantin in the fruit.