Impact of ultrasonic pretreatment on the color and antioxidant capacity of vacuum freeze-dried strawberries

To enhance the color quality and antioxidant potential of vacuum-freeze-dried strawberry tablets, ultrasonic waves were used as a freezing pretreatment. Results revealed that the * values of freeze − dried strawberries following ultrasonic pretreatment improved significantly by ∼60% and the C* values increased by 34.36%–51.65%. These findings suggest that ultrasonic pretreatment results in a brighter coloration of the strawberry samples. The ultrasound − assisted freezing treatment groups exhibited a significantly higher free radical scavenging ability compared with the nonultrasonic treatment group. This enhancement was attributed to the ultrasonic pretreatment, which increased the concentrations of total phenolic compounds, flavonoids, and anthocyanins, and effectively inhibited the activities of polyphenol oxidase and peroxidase, thereby reducing the content of red pigment in the strawberry samples. Furthermore, confocal laser scanning microscopy revealed a uniform distribution of sugar within the samples following ultrasonic treatment. Cluster analysis indicated that the primary indices influencing the color of the samples were total phenolic content and peroxidase activity. Therefore, the ultrasonic pretreatment method effectively enhances product color, inhibits enzyme activity, and increases anthocyanin content. This technology holds promising development prospects.