Abstract: The effect of hot water blanching and steam blanching treatments on the activity of endogenous browning-related enzymes such as polyphenol oxidase (PPO) and peroxidase (POD), and the microstructure of lily pieces were investigated. Results showed that PPO activity was higher than POD activity in fresh lily bulbs. The thick outer pieces (TKO) show the highest PPO activity, while the lowest one was observed in the thin inner pieces (TNI). POD activity was highest in the thin outer pieces (TNO) but was lowest in TNI. The activity of PPO and POD was effectively inhibited by both thermal treatments. The microstructure of the cross section and the adaxial epidermis of lily bulb pieces was changed after the blanching treatments. PPO in the TNO and the TNI was inactivated after more than 30 s of thermal treatments, while POD was inactivated when the blanching time was more than 60 s. The blanching time required to inactivate PPO and POD in the TKO and the thick inner pieces was more than 60 and 120 s, respectively. Blanching resulted in gelatinization of lily starch granules with surface textures changing from smooth to coarse, blurring the interface between starch granules. The degree of gelatinization increased with blanching time and the time required to completely gelatinize lily starch granules was 3 min. No stomatas were distributed in the adaxial epidermis. The surface of lily bulb pieces became more smooth and showed membranous and granular structures after blanching treatments.

Key words: lily, blanching, browning, endogenous enzymes, microstructure