Quality changes in Pteridium aquilinum and the root of Platycodon grandiflorum frozen under different conditions

• Different freezing methods affect the quality of frozen bracken fern and bellflower.
• Freezing produced considerable changes in the microstructure.
• The least changes in the samples were produced by freezing at −70 °C.
• Freezing in the gas nitrogen convection chamber at −70 °C was the most suitable.

The effects of different freezing methods on the quality changes of bracken fern and the root of bellflower were examined. Quality characteristics, such as the microstructure, hardness, colour, and sensory properties of these vegetables, were determined after freezing at −20 °C in a freezer, at −70 °C in a gas nitrogen convection chamber, and at −196 °C in liquid nitrogen. Freezing produced considerable changes in the microstructure, hardness, colour, and sensory parameters of the bracken fern and bellflower root samples. The highest degree of changes in the microstructure and hardness of the vegetables were induced by freezing at −20 °C, whereas the least changes were produced by freezing at −70 °C. Based on the sensory characteristics, freezing at −70 °C provided the highest acceptability of the vegetable samples. Therefore, freezing in the gas nitrogen convection chamber at −70 °C is suggested to be the most suitable freezing method.