Effect of ultrasonic-assisted blanching pretreatment on the characteristics of solar-heat pump dried pumpkin slices

In order to demonstrate the influence of ultrasonic-assisted blanching pretreatment on the characteristics of solar-heat pump dried pumpkin slices, the effects of ultrasonic temperature, ultrasonic power, frequency and treatment time on the chromatic aberration, hardness, content of β-carotene and ascorbic acid were studied. The optimum technological conditions were obtained by orthogonal optimization analysis and compared with the traditional blanching pretreatment for drying the quality of pumpkin. The results revealed that under the conditions of ultrasonic temperature of 70℃, ultrasonic power of 300 W, ultrasonic frequency of 35 kHz and ultrasonic treatment time of 3 min, drying treatment had the least effect on the color and nutrient content of pumpkin slices. The chromatic aberration was 9.95, compared with traditional blanching, the chromatic aberration decreased by 61.64%. The hardness value was 36.61 N. The content of ascorbic acid was 13.00 mg/100 g, which was 41.38% higher than the traditional blanching treatment. Therefore, the advantages compared to the traditional hot stamping method are still obvious. It was proved that the physical means of ultrasound can significantly reduce the color change of pumpkin heat treatment and the loss of ascorbic acid and other nutrients, and the ultrasonic blanching pretreatment method owned the potential of being applied in the drying process of pumpkin slices.