Evaluation of the Effect of Refractive Window Drying Using Ultrasound as Pretreatment on the Preservation of the Chemical, Physical and Techno-Functional Properties of the Leaf of Bauhinia forficata

Bauhinia forficata leaves were subjected to ultrasonic pretreatment and subsequently dried using a refractance window (RW) and tray drying (TD). The physical, chemical, and biological properties of the dried leaves were evaluated under both drying methods, with and without ultrasound. RW combined with ultrasound (RW-US) resulted in the shortest drying time (90 min) and the lowest values of water activity (0.21), color difference (ΔE = 0.61), and maximum shear force (14.72 N), indicating improved drying efficiency and texture preservation. In addition, the RW-US samples exhibited the highest water solubility capacity (13.75%), water absorption capacity (5.56 g water/g dry matter), and swelling power (9.95%). With respect to structural changes, thickness showed the greatest percentage reduction during drying. The RW-US treatment also preserved bioactive compounds more effectively, yielding the highest total polyphenol content (61.96 mg GAE/g extract), flavonoid content (308.44 mg QE/g extract), antioxidant activity (60.50% by DPPH• and 70.15% by ABTS•+), and chlorophyll content (2.65 mg/g), the values of which were closest to those of fresh leaves. None of the extracts showed cytotoxic effects, with respect to hypoglycemic activity, the best treatments were RW, RW-US, and TD, which resulted in glucose reductions of 51.64%, 41.95% and 39.70%, respectively. Overall, RW-US drying preserved most of the physical, chemical, and biological properties, resulting in the production of a potential functional ingredient for foods.