Different Drying Techniques and Their Impact on Physicochemical Properties of Sweet Potato: A Review

Sweet potato (SP) is a globally important storage root crop, serving as a natural source of essential nutrients, including starch, carotenoids, and anthocyanins. Given its nutritional value, preserving the physicochemical properties during processing is imperative to enhance its role in addressing food security. This review presents a comprehensive analysis of the literature on physicochemical properties, such as color, β-carotene, and TPC and examines the effects of different drying techniques on these properties. It was found that CHAD significantly degrades these properties, potentially reducing the β-carotene content by up to 22.7-fold and the TPC by 53%. This degradation can result from high drying air temperatures (>70°C), high air velocity (>1.5 m.s^-1) and extended drying times, which can be up to 28 h. In contrast, combined techniques preserve these properties. For example, MWD + CHAD reduced the drying time up to six times more than CHAD alone. In addition, MWD + CHAD achieved a lower total color change (ΔE) and a higher retention of β-carotene content (67%). The highest increase in TPC (247%) was observed for SP that was dried using MWD with carbon maceration pre-drying treatment. This results from a porous microstructure that is formed which increases the moisture transfer and reduces the drying time. Factors like the drying air temperature, drying medium, air velocity, and pre-drying treatments influence the performance of drying techniques and their quality preservation capabilities. However, the SP variety is often overlooked in drying studies. This article discussed, compared, and identified literature gaps to pave the way for future research aimed at enhancing dried SP product quality.