Effect of different drying methods on physico-functional properties and anthocyanins of purple-fleshed sweet potato flours

In order to improve the quality of purple sweet potato flours and retain the nutritional value, effects of hot air drying, drum drying and vacuum freeze drying on physic-functional and anthocyanins of flours prepared from purple sweet potato variety Q-18 were evaluated.The color, granule structure, water absorbing capacity and freeze-thaw capacity, granule structure, content and components of total anthocyanins were measured.The results showed that different drying methods had effect on the physic-functional properties and content of anthocyanins of purple sweet potato flours ( p < 0.05) . Flours prepared by vacuum freeze drying could keep the color and aroma better and the water absorbing capacity ( 6.900 g/g) , freeze-thaw capacity ( 0.171 g/g) and anthocyanin content ( 5.030 mg/g DW) were better than the other two drying methods.Flours prepared by drum drying were also in good quality as the water absorption capacity, freeze-thaw capacity and anthocyanins content were 6.185, 0.341 g/g DW and 4.047 mg/g DW respectively. Hot air drying had a significant effect on the content of anthocyanins ( 2.094 mg/g DW) . It was nearly half of the drum drying.LC-MS showed that drying methods had little effect on the types of anthocyanins, while it could affect the total content and relative content of anthocyanins.Some organic acids tended to drop when heating.In a word, the quality of flours prepared by drum drying is good, second only to freeze drying, which is suitable for large-scale industrialization.As a result, drum drying is a good choice for the preparation of purple sweet potato flours.