Nutritional, pasting, rheological, and thermal properties of sorghum–okara composite flours and porridges

Abstract This study examined the impact of okara addition on the nutritional, pasting, rheological, and thermal properties of sorghum flour and porridge. Porridges (fermented and unfermented) were made with 100% sorghum flour and sorghum–okara blends at 70:30 and 50:50 ratios. The inclusion of okara significantly enhanced the porridge's crude protein, fat, fibre, and ash content. It also increased essential amino acids, particularly lysine, and improved in vitro protein digestibility and available lysine by 23%–73% and 50%–104%, respectively, compared to 100% sorghum porridge. Okara addition and fermentation altered pasting properties, reducing peak viscosity (PV), holding strength, breakdown viscosity, and final viscosity while also decreasing the storage modulus (G′) and loss modulus (G″). Differential scanning calorimetry showed that sorghum flour had higher thermal stability than okara, but this stability decreased with the addition of okara. In terms of colour, the blending of sorghum and okara, along with fermentation, led to noticeable shifts in colour, making the porridges brighter and more colourful. Overall, okara was found to improve the nutritional quality and colour attributes of sorghum-based porridge while also affecting the pasting and thermal properties by reducing its PV and gelatinization temperature.