Effect of foam-mat drying conditions on drying rate and anthocyanin content in purple sweet potato powder

<br />The study aimed tooptimise foam-mat drying parameters for producing purple-fleshed sweet potato (PFSP) powder. Egg albumin (EA) (5–15%), xanthan gum (XG) (0.1–0.5%), and drying temperature (50–70C) were used asindependent variables for optimisation via Response Surface Methodology with aBox-Behnken design. The response variables (drying rate and anthocyanin content) were assessed by18treatments, which included 6central points. The analysis ofvariance showed ahigh coefficient ofdetermination (>88%) between predicted and experimental values across all models. Optimal foam-mat drying conditions were 11.02%EA, 0.34%XG, and 65.1C toachieve the highest drying rate (2.49 g water.g dry matter^–1.min^–1) and anthocyanin content (1.01 mg.g^–1). After 3.5h ofdrying at65.1C, the foam-mat dried PFSP showed alow moisture content (4.35%) and water activity (0.29). Its water solubility index, water absorption index, rehydration ratio, total polyphenols, and antioxidant activity were determined tobe56.49%, 3.55%, 3.82, 3.66± 0.06 mg GAE.g^–1, and 58.49± 0.88%, respectively. Under these conditions, the powder maintained its natural beautiful and characteristic purple colour. The microstructure ofthe foam-mat dried PFSP powder (via SEM images) was also observed.