The influence of pretreatments on the quality characteristics and in vitro biological activity of freeze-dried Thai Tom-Yum ingredients

Abstract

This study aimed to investigate the effects of pretreatments on quality characteristics, bioaccessibility of phenolic compounds, and antioxidant activities (AA) of freeze-dried Thai Tom-Yum ingredients during in vitro digestion. Hot water (B), steam (S), microwave blanching (MW), ultrasound (US), and blanching with dipping in chemical solution (D) were performed on lemongrass, red onion, kaffir lime leaves, chili, galangal, and coriander. In most samples, D significantly lowered water activity (Aw) and moisture content (MC) while preserving color attributes. D was the best pretreatment with the highest total phenolic compounds (TPC) for lemongrass, red onion, and galangal, US for kaffir lime leaves and chili, and S for coriander. The AA assessed by DPPH and FRAP showed a correlation with TPC values (0.731 and 0.576 at p < 0.01). Bioaccessibility of phenolic compounds and FRAP in selected herbs were higher under intestinal phase. After digestion, kaffir lime leaves treated with US had the highest TPC and FRAP values, ranging from 26.63 to 34.34 mg GAE/g db and 80.07–105.07 μmol FeSO4/g db, respectively. A decrease in DPPH values was observed in lemongrass, red onion, chili, and galangal. These findings show that pretreatments and freeze-drying have considerable effects on the qualitative attributes, bioaccessibility of phenolic compounds, and AA of dried herbs.