EFFECT OF EXTRUSION TEMPERATURE AND MOISTURE ON PHYSICAL, FUNCTIONAL AND NUTRITIONAL PROPERTIES OF KABULI CHICKPEA, SORGHUM, MAIZE AND THEIR BLENDS

The overall goal of this research was to investigate extrusion and the effect of extrusion temperature (120 and 150oC) and moisture (20 and 24%) on the physical, functional and nutritional properties of raw and/or extruded Kabuli chickpea, sorghum and maize flours in the first study, as well as their blends (chickpea-cereal) in the second study. The extrudates were analyzed for physical properties—expansion ratio, bulk density and hardness, and were then milled into flours for functional properties including water hydration capacity, oil holding capacity, foaming capacity and stability, emulsion activity and stability, and pasting property; in vitro protein digestibility and in vitro protein digestibility corrected amino acid score were analyzed for nutritional properties, and were compared to the WHO/FAO requirement for protein quality to determine the feasibility of the blends to be used as a food aid product or other potential applications. Nitrogen solubility and thermal properties were analyzed for some samples to demonstrate the effect of extrusion on protein solubility and starch gelatinization respectively. The effect of extrusion temperature and moisture on different properties varied among samples. Generally, higher temperature and lower moisture content resulted in greater expansion, less hardness and bulk density. Extrusion reduced protein solubility and gelatinized/melted all detectable starch, which affected the functional and nutritional properties of the flours. Extrusion significantly increased (2-3 times) water hydration capacity, whereas decreased pasting viscosities (8-40 times) due to shear and gelatinization of starch. Oil holding capacity slightly decreased for the blends but remained relatively unchanged at the same level for the individual flours. None of the extruded samples showed foaming activity. Emulsion properties varied for the individual flours but showed a general decrease for the blends. Extrusion did not improve protein quality (in vitro protein digestibility corrected amino acid score) of the blends by much due to the loss of limiting amino acid lysine. Only chickpea-maize blend reached the 70% requirement by WHO to be used as food aid for the moderately malnourished. The great hydration property of the extrudates indicates the potential use as instant cold/hot beverage or porridge