Effects of ultrasound pretreatments on the quality of fried sweet potato (Ipomea batatas) chips during microwave‐assisted vacuum frying

Abstract The research was focused on the quality of sweet potato chips fried by microwave‐assisted vacuum frying (MVF) pretreated by ultrasound. Fresh sweet potato slices were pretreated at two different ultrasonic conditions: (1) ultrasound power of 150, 300, and 450 W for 20 min and (2) ultrasound power of 300 W for 10, 20, and 30 min. The pretreated samples were then fried by MVF. The dielectric properties, drying time, moisture content, oil uptake, texture, color, and microstructure profiles of the fried sweet potato chips were measured to determine the effects of ultrasound pretreatments on the quality of the fried sweet potato slices. This study found that the dielectric properties of the fresh sweet potato slices was significantly (p < .05) changed by ultrasound pretreatments. The moisture content and oil uptake of the fried sweet potato chips was reduced constantly by increasing the ultrasound pretreatments power and prolonging the processing time. The stronger ultrasound power and the longer processing time resulted into a crispier texture property of the fried sweet potato chips. However, the strong ultrasound power level and the prolonged processing time also caused the negative effect on the color preservation and cell integrity of fried samples. In conclusion, a proper ultrasound power level and time have to be selected to produce fried sweet potato chips with less oil uptake, crisper texture, and better appearance. Practical applications Ultrasound pretreatments have great potential to improve the quality of fried food products. Ultrasound pretreatment before frying is a novel method for fabricating food products with healthier attributes, better appearance, more natural color and less frying time. The research found that, ultrasound pretreatments with proper ultrasound power level and processing time can produce higher quality products and shorten frying time.