Pretreatment and Freezing Rate Effect on Physical, Microstructural, and Nutritional Properties of Fried Sweet Potato

Sweet potato is a unique high-calorie food because it is an excellent source of some essential micronutrients, such as provitamin A (ß-carotene). The quality of par-fried frozen sweet potato products is impacted by several factors that have not been well researched, such as freezing rate and surface modification. In this study, our objective was to evaluate the effect of freezing rate (at -20°C, -30°C, -40°C, and -60°C), surface pretreatment including blanching and gum coating (methylcellulose, sodium alginate, or mixed gums), sample dimensions (strips or slices), and cultivar (Covington and Murasaki) on several quality attributes of fried sweet potato. Based on our study, frying at 180°C yielded the lowest oil content among the tested temperatures. Compared with Covington samples, Murasaki strips coated with mixed gums produced fried samples that were significantly (p = 0.05) lower in fat uptake (10.84%), less porous (35.5%), crispier (maximum force = 6.90 N), lighter, less red, and yellower. Higher freezing rate, 5.12°C min-1 (at -60°C), showed significantly lower fat content, and lower lightness or yellowness than lower freezing rates. Frying at 180°C significantly reduced vitamin C and ß-carotene levels from 3.75 mg and 349.27 µg per 100 g to 1.92 mg and 105.99 µg per 100 g, respectively. X-ray micro-computed tomography showed a significant decrease in porosity because of high freezing rates. The general conclusion is that faster freezing rate is better for par-fried sweet potato quality preservation. Keywords: ß-carotene, Fat uptake, Gum coating, Par-frying, Sweet potato, X-ray micro-computed tomography, Vitamin C.