Impact of Superheated Steam Drying on Millet Analogue Rice: Evaluation of Textural, Cooking, Functional, and Structural Properties

Abstract

This study investigated the effects of super-heated steam drying (SSD) on the textural, functional, cooking, rheological, and structural characteristics of millet analogue rice (MAR), formulated from pearl millet, sorghum, and parboiled rice through hot extrusion technology. Drying experiments were conducted at varying temperatures (120°C, 140°C, and 160°C) and thicknesses (2 mm, 4 mm, and 6 mm). Their impact on quality parameters, including water absorption index (WAI), color difference (ΔE), water absorption ratio (WAR), cooking loss (CL), water solubility index (WSI), and cooking time (CT), was analyzed and optimized using the Central Composite Design (CCD) within the framework of Response Surface Methodology (RSM). Optimal drying conditions were identified at 120°C and 2 mm thickness, achieving a ΔE of 3.51, a CT of 28.74 min, a WAR of 7.12, a CL of 8.06%, a WAI of 3.45 g/g, and a WSI of 6.23%, with a desirability value of 0.969. The optimized drying parameters significantly influenced the pasting and textural attributes of MAR (p < 0.05) compared to undried MAR. Rheological analysis demonstrated that both super-heated steam-dried and undried MAR exhibited superior elastic properties relative to viscosity. FTIR spectroscopy revealed modifications in the spectral region of 900–1100 cm⁻¹, indicating higher crystallinity in the dried MAR. Differential Scanning Calorimetry (DSC) analysis indicated reduced onset temperature and enthalpy, suggesting partial gelatinization and loss of crystalline order due to drying. Furthermore, scanning electron microscopy (SEM) revealed smoother and flatter surface morphology in the dried MAR compared to undried MAR. Overall, the findings elucidate the role of super-heated steam drying in enhancing the quality and structural integrity of MAR, thereby contributing to the development of superior MAR under optimized drying conditions.