Abstract:The solubility of κ-carrageenan was improved by ultrasonic treatment for different time periods （0-240 min）.The effects of ultrasonic treatment on the molecular weight，reducing sugar content，solubility，thermal stability，rheology，and gel texture of carrageenan were studied，on the basis of which the mechanism of ultrasonic treatment on the structure and functional properties of κ-carrageenan was explored.The results showed that the molecular weight，reducing sugar content，and solubility of κ-carrageenan were greatly influenced by ultrasonic time.Ultrasonic treatment can significantly reduce the molecular weight，and the water solubility index of the sample at room temperature can reach 98.91% after 60 min of ultrasonic treatment.The variation in reducing sugar content with ultrasonic time indicated that ultrasonic treatment can depolymerize and partially degrade κcarrageenan，thus improving its solubility.The changes of rheology and gel structure suggested that ultrasound regulated the viscoelastic properties of the carrageenan samples.Before ultrasonic treatment，κ-carrageenan was a hard and brittle gel with certain water secretion.After ultrasonic treatment，the sample showed increased water-holding capacity and decreased thermal stability.The results of scanning electron microscopy suggested that ultrasound changed the apparent morphology of the sample.With the extension of ultrasonic time，the sample showed extended surface folds，smoothing surface，and flaky microstructure.To sum up，ultrasound as an effective method to improve the solubility of polysaccharides including κ-carrageenan can regulate the rheology and gelation，enhance the water-holding capacity，and reduce the thermal stability of κ-carrageenan.