Effect of hydration and thermal pre-treatments on physicochemical properties and stability of sorghum-millet blended milk

This study explored a synergistic pre-processing approach integrating hydration and thermal treatments to improve yield, nutrient retention, and functional quality of a sorghum and millet blended milk (sorghum: pearl millet: proso millet = 1:1:1). Three hydration methods, viz. , conventional soaking, alkaline soaking (0.05% sodium bicarbonate, NaHCO₃), and ultrasound hydration (20 kHz, 26 min), were evaluated. The optimally hydrated grains were subsequently subjected to thermal treatments such as microwave (750 W, 2.5 min) and blanching (90 °C, 5 min). Alkaline soaking significantly improved total solids, protein (0.47 ± 0.01 g/100 mL), and viscosity, while reducing titratable acidity and phytate content of the sorghum-millet blend milk relative to other hydration methods. Ultrasound hydration produced finer particle size and greater ζ-potential, indicating enhanced colloidal stability but lower nutrient recovery. Among the thermal treatments of alkaline-soaked grains, microwave heating increased milk yield by 4.7% and protein by 73.7%, whereas blanching caused excessive starch gelatinisation, aggregation, and reduced stability (CSR = 31.8%). Overall, alkaline soaking followed by microwave heating was the most effective for enhancing yield and nutrient recovery. Nevertheless, further processing and formulation optimisation are needed to enhance nutritional quality and stability; this study provides a critical foundation for developing nutrient-rich sorghum–millet blend milk. • Alkaline soaking (0.05% NaHCO₃) enhanced yield, protein, and total solids. • Ultrasound hydration yielded finer particles and enhanced stability but reduced nutrient recovery. • Microwave heating (750 W, 2.5 min) increased yield by 4.7% and protein by 73.7%. • Blanching caused excessive gelatinisation, aggregation, and reduced stability.