LAUSR

BACKGROUND Blanching is a unit operation prior to drying of vegetables. Hot water blanching (HWB) of broccoli brings about quality decline and environmental problem. In this work, hot air assisted radio frequency heating blanching (HA-RFB) of broccoli was developed prior to further drying process. Blanching sufficiency, heating uniformity and heating rate during HA-RFB were investigated to improve the product physicochemical properties and texture. A desirable heating rate and uniformity was achieved with radio frequency assisted by 70°C of hot air under 10.7 cm of electrode gap, using cylindrical container for broccoli. RESULTS Under this condition, the relative peroxidase activity in broccoli decreased to 3.26% within 117 s, with 13.45% of weight loss. Compared to HWB broccoli, the products blanched by HA-RFB preserved better texture, bioactive compounds, as well as the microstructure. In addition, the content of ascorbic acid, sulforaphane and total glucosinolates in HA-RFB products were 251.1%, 131.9% and 36.7% higher than those in HWB broccoli. Furthermore, HA-RFB treatment led to a higher weight loss (13.45±0.50%) than HWB (8.70±1.70%), which is greatly beneficial to the subsequent drying process. CONCLUSION This study demonstrated that HA-RFB could be a promising substitute of HWB to blanch broccoli and other flower vegetables, especially as a pretreatment of drying process. This article is protected by copyright. All rights reserved.