Two-stage frying process for high-quality sweet-potato chips

Vacuum frying (1.33kPa), with the aid of a de-oiling mechanism, was used to produce low-fat sweet potato chips. The kinetics of oil absorption and oil distribution in the chips (total, internal, and surface oil content) was studied so that effectiveness of the de-oiling system could be established. Product quality attributes (PQAs) such as moisture content, oil content, diameter shrinkage, and thickness expansion, as well as, color, texture, bulk density, true density, and porosity of chips fried at different temperatures (120, 130, and 140°C) was performed to evaluate the effect of process temperature on the product.The final oil content of the vacuum fried chips was 60% lower than those found in traditionally fried sweet potato chip, which indicates that the de-oiling mechanism is crucial in vacuum frying processing. The rate of change in PQAs is greatly affected by temperature; however, the final values of bulk density, true density, porosity, diameter shrinkage, and thickness expansion were not affected by temperature. The structured of the chips settled faster when fried at 130–140°C. Color b∗ values was not affected by temperature by the range of temperature used in this study.The product fried in a two-stage (TS) frying process (1min fried at atmospheric pressure and 2min under vacuum) had better appearance and texture compared to the ones that were only fried under vacuum or single-stage (SS) conditions. The samples were lighter and more yellow (less compact) than the chips fried under the SS process. The atmospheric frying prior to vacuum frying helped the starch to gelatinize thus producing a better product in terms of texture, oil content, and flavor. The final oil content of the TS fried chips was 15% lower than those fried by the SS process showing that the structure of the chips formed during the process affected the oil absorption during frying.