Effects of high-humidity hot air impingement steaming on Gastrodia elata: steaming degree, weight loss, texture, drying kinetics, microstructure and active components

Steaming is a key process affecting quality of herbal medicine Gastrodia elata (G. elata). This research investigated the effects of high-humidity hot air impingement steaming (HHAIS) on weight loss, texture, drying characteristics, microstructure, and active ingredients of G. elata, as well as the judgement of steaming degree. It was demonstrated that G. elata steaming degree was correlated to starch gelatinization and could be quantified by monitoring central temperatures of the cross section with the maximum diameter. While just well-steamed, the G. elata central temperature was around 62.8–67.2 ℃, near to gelatinization temperature. Steaming led to decreased weight and shear hardness, while increased adhesion force and prolonged drying time. Hydrolysis of polysaccharide and gelatinization of starch granules were observed from microstructure of steamed G. elata, which confirmed changes in weight, texture and drying rate. Furthermore, steaming increased gastrodin content and decreased p-hydroxybenzyl alcohol content.