Effect of processing on functional properties, physicochemical characteristics and in vitro starch digestibility of two sweet potato varieties

Abstract

This study investigates the effect of different processing methods (boiling, baking, and frying) on the functional properties, physicochemical characteristics and in vitro starch digestibility of two sweet potato varieties: Guayaco morado and Toquecita. Thermal processing affected the rate of starch digestion, focusing on parameters, such as total digestible starch (TDS), rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS), from which the hydrolytic index was determined and allowed estimation of the glycemic index (pGI) to be derived from sweet potato intake. Each cooking technique has a unique impact on sweet potatoes. For example, boiling maximizes starch gelatinization (improving digestibility) but leaches water soluble nutrients, baking develops desirable flavors and retains carotenoids, although high temperatures can form acrylamide and frying increases resistant starch which reduces glycemic impact, it also leads to decreased starch solubility and creates crisp textures but introduces excess calories and potential heat contaminants. Among the varieties studied, Toquecita exhibited higher TDS (73.75 ± 0.18 g/100 g dw) and RDS (31.21 ± 0.10 g/100 g dw) in boiled samples, while fried samples showed a higher RS content (9.83 ± 0.03) compared to Guayaco morado. This difference reflects Toquecita’s lower amylose content and water absorption index. Both varieties exhibited a lower glycemic index (pGI) in the raw state. However, among the processed samples, the fried Guayaco morado variety displayed a lower pGI (64.15 ± 0.89). These results emphasize the significant impact of cooking methods on the nutritional profile of sweet potato starch. The findings suggest that boiling and baking are processes for enhancing starch digestibility, while frying may diminish it. Overall, this study highlights the potential of sweet potatoes as a functional food ingredient, particularly for diets with a moderate glycemic index.