Effects of ultrasonic impregnation pretreatment on drying characteristics of Nostoc sphaeroides Kützing

The purpose of this study was to investigate the effects of ultrasonic impregnation pretreatment on drying characteristics of Nostoc sphaeroides Kützing (N. sphaeroides). N. sphaeroides treated with ultrasound and the ultrasonic solution contain 1% salt, 6% whey protein, and 15% xylitol/sucrose/trehalose. The results showed that N. sphaeroides treated with ultrasonic solution containing 1% salt, 6% whey protein, and 15% xylitol had the best quality. Freeze-drying (FD), pulse-spouted microwave freeze-drying (PSMFD) and hot air drying (AD) were used respectively to dry ultrasonic impregnated N. sphaeroides. Then, the color, texture, flavor, ascorbic acid, antioxidant capacity, and rehydration ratio of different products were determined. The results showed that the qualities of the PSMFD products were similar to that of the freeze-dried products, but its antioxidant activity was obviously higher than that of the freeze-dried product. PSMFD also had the advantages of short drying time and low energy consumption.