Influence of different drying techniques on physicochemical and techno-functional properties, gelatinization, pasting behaviors, and morphology of bitter yam (Dioscorea bulbifera L.)

Abstract

This study investigates the influence of various drying methods—sun drying (SD), shade drying (SHD), hot air drying (HAD), microwave drying (MWD), infrared drying (IRD), and freeze-drying (FD)—on the physicochemical, nutraceutical, structural changes, and pasting properties of bitter yam flour. Scanning electron microscopy (SEM) analysis revealed that FD samples retained the original starch granule structure, while HAD and MWD samples exhibited substantial damage and variation in particle sizes. FD samples exhibited the highest levels of resistant starch (50.23 %), while IRD and MWD showed lower resistant starch levels (2.05 % and 2.03 %, respectively). Modern drying methods (HAD, MWD, IRD, and FD) achieved a moisture content of less than 10 %, ensuring safer, longer storage, with FD achieving the lowest moisture content (6.07 %). The HAD sample demonstrated the highest peak viscosity (732.17 mPas), suggesting better starch stability compared to MWD (377.17 mPas) and IRD (598.37 mPas). Nutraceutical analysis indicated that FD samples had retained the highest total flavonoid content (75.77 mg/g) and antioxidant activity (FRAP = 21.99 mM Fe (II)/g). These findings suggest that FD, compared to traditional drying methods, preserves the nutritional and functional properties of bitter yam flour.