Steam blanching strengthened far-infrared drying of broccoli: Effects on drying kinetics, microstructure, moisture migration, and quality attributes

The effects of steam blanching (SB) at various times (0, 30, 60, 90, 120, and 150 s) on the far-infrared drying kinetics, quality properties of broccoli, and relevant mechanisms were investigated. Compared with the un-treated samples, SB increased the drying rate, and reduced the drying time by 9.26%-48.15%. The back propagation-artificial neural networks (BP-ANN) was optimized and performed the good fitting performance between drying time, blanching time and moisture ratio, with the best training function of trainlm, transfer function of tangsig in input-hidden layer and purelin in hidden-output layer, and 10 hidden layer neurons. Meanwhile, SB destroyed the cellular structure, that caused the collapse of the tissue and the increase of water freedom, and which were intensified by prolonging the blanching time. Blanched sample after drying had better color, higher chlorophyll and vitamin C contents, while the retention of sulforaphane decreased slightly after blanching compared with the untreated broccoli.