Effect of drying and salting on the flavour compound of Asian white radish

Asian white radish (Raphanus sativus cv. Hoshiriso) was dried to <10% moisture using a hot air drier at 40, 50 60 and 70 °C, a heat pump drier at 35, 40, 45 and 50 °C and a freeze-drier, and was salted under pressure with concentrations of 0, 5, 15 and 25% sodium chloride. The primary compound responsible for the flavour of white radish, 4-methylthio-3-trans-butenyl isothiocyanate (MTBITC), was found to be substantially decreased by the hot air and heat pump driers, the loss increasing with increasing drier temperature, but the loss was lower in the heat pump drier than the hot air drier at equivalent temperatures. Osmotic dehydration with salt also caused a substantial loss of MTBITC with the loss increasing with increasing salt concentration. MTBITC loss of about 50% occurred with a heat pump drier at 50 °C, hot air drier at 40 °C and 25% salt. Freeze-dried white radish showed a relatively low loss (15% MTBITC).