High moisture extrusion of lupin protein: influence of extrusion parameters on extruder responses and product properties

BACKGROUND
High moisture extrusion (HME) of lupin protein concentrate and isolate (50:50) mixture was performed by varying the extrusion parameters, such as barrel temperature (138–180 °C), water feed (40–68%) and screw speed (400–1800 rpm). The effect of extrusion parameters on extruder responses [die pressure, product temperature, torque and specific mechanical energy (SME)] and product properties [colour, cutting force, cooking yield, microstructure and in vitro protein digestibility (IVPD)] was evaluated.

RESULTS
The multiple regression analysis of the results revealed that the water feed had a significant negative linear effect on the extruder responses considered, as well as on colour difference and cutting force of extrudates. Screw speed had a positive linear effect on product temperature, SME and cooking yield. Barrel temperature affected extruder responses and product properties to a lesser extent. Scanning electron microscopy showed that denser microstructure and higher number of fibre layers were created by increasing temperature and screw speed along with decreasing water feed. The results of IVPD of selected extrudates showed that the increase in barrel temperature decreased the IVPD, whereas the increase in water feed resulted in higher IVPD. The screw speed had no significant effect on IVPD.

CONCLUSION
The study demonstrates that the use of lupin protein is feasible to produce meat analogues with HME which could enhance the possibilities to meet the growing protein demands for human consumption.