Thermal characterisation of corn–lentil extruded snacks

The phase transitions of extruded corn–lentil snacks were investigated using different extrusion process conditions, which were feed rate (2.52–6.84 kg/h), extrusion temperature (170–230 °C) and feed moisture content (13–19% wb). Lentil flour–corn flour mixtures were used at ratios ranging from 10–50%. Extrusion temperature, feed rate and feed moisture content decreased the specific mechanical energy during extrusion cooking. The sorption isotherm at room temperature of corn–lentil snacks was described successfully by the GAB model. The glass transition temperature of extrudates (midpoint of the specific heat shift) increased with feed rate, extrusion temperature, and lentil to corn ratio. Water acts as a plasticiser on extrudates, depressing their glass transition temperature. The Gordon-Taylor equation was used for the plasticisation description and had a good fit with the experimental data. Generally, as the moisture content decreased, the sharpness of glass transition also decreased. The formation of amylose–lipid complexes was confirmed by the presence of an endothermic peak.

Research highlights
► The water sorption of extruded corn–lentil snacks was described by GAB model.
► The Tg of extrudates was influenced by extrusion conditions and feed composition.
► The plasticizing effect predicted by Gordon-Taylor equation.
► During extrusion cooking complexes are formed between amylose and lipids.