Effects of Drying Techniques on Selected Functional Properties and Bioactive Compounds of Dietary Fiber from the Outer Leaves of Cabbage

Abstract

The outer leaves of cabbage (Brassica oleracea L. var. capitata), which are usually discarded during processing or selling at the market, have been reported as a good raw material for producing functional dietary fiber powder. This study investigated the effects of different drying techniques, i.e., hot-air drying, vacuum drying and low-pressure superheated steam drying at 80°C, on selected functional properties and bioactive compounds of dietary fiber powder from the outer leaves of cabbage. The results showed that vacuum drying improved water retention capacity and swelling capacity of the dietary fiber powder compared to the hot-air dried sample. Neither the pressure level (5 and 10 kPa absolute pressure) nor steam injection before vacuum drying at 10 kPa affected the water retention or swelling capacities of the powder. No significant differences in the oil holding capacity (OHC) were observed among the samples prepared using different drying schemes. Vacuum-dried samples contained the highest contents of glucosinolates and phenolics. Overall, the results showed that powder undergoing vacuum drying at 80°C at 5 kPa possessed good functional properties and contained the most glucosinolates and phenols.