Effect of barrel temperature and feed moisture on the physical properties of chickpea–sorghum and chickpea–maize extrudates, and the functionality and nutritional value of their resultant flours—Part II. Issue 4 (17th May 2019) - Wang, Shuyang
Abstract: Background and objectives: The effect of barrel temperature (120 and 150°C, held constant in zones 4–6) and feed moisture (20% and 24%) on the physical properties of chickpea–sorghum (CS) and chickpea–maize (CM) extrudates, and the functional and nutritional properties (protein quality) of their flours were examined. Findings: Temperature had a greater effect on the physical properties than moisture for both blends, where, in general, extrusion at 150°C resulted in greater expansion, less hardness, and lower bulk density than at 120°C. Extrusion also increased the water‐holding capacity relative to the raw CS and CM blends, but had an adverse effect on oil‐holding capacity, foaming, and emulsifying properties. Pasting viscosities of precooked flours were also lowered by 8 to 37 times due to the pregelatinization of the starch. Although in vitro protein digestibility increased after extrusion, the in vitro protein digestibility‐corrected amino acid score (PDCAAS) showed an overall reduction relative to the raw blended flours due to the reduction of the primary limiting amino acid lysine during extrusion. Conclusions: Only the chickpea–maize blend extruded at 120°C at either 20% or 24% moisture had higher in vitro PDCAAS than the raw blend, with only the one with 24% moisture having a value >0.70. Significance and novelty: A balance between functionality and protein quality needs to be considered when using extruded pulse–cereal blends.