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The effect of the addition of Spirulina platensis flour and of extrusion parameters on texture, cooking yield, expressible moisture, total phenolic content (TPC), total flavonoid content (TFC), Trolox equivalent antioxidant activity (TEAC), in vitro protein digestibility (IVPD) and conformational changes of proteins using Fourier-transform infrared spectroscopy (FTIR) of lupin protein based meat analogues was studied. High moisture extrusion (HME) cooking was used to produce the meat analogues. The Spirulina concentration (15, 30 and 50%), extruder barrel temperature (145 °C, 160 °C and 170 °C), water feed (50, 55 and 60%), and screw speed (500, 800 and 1200 rpm) were varied. The Spirulina concentration and extrusion parameters significantly affected physical properties, such as texture, cooking yield and expressible moisture of the extrudates. The addition of Spirulina generally increased the TPC, TFC and TEAC values of the extrudates. Increased temperature and screw speed as well as decreased water feed slightly improved the content of TPC, TFC and TEAC, respectively. The addition of Spirulina at a level of 30% decreased the IVPD of the extrudates from 82 to 75.6%. However, increased water feed and screw speed partly counterbalanced this effect. Protein conformational analyses of the extrudates by FTIR showed that β-sheets were decreased, whereas α-helix, β-turn and antiparallel β-sheets were increased compared to the raw extrusion mixtures. On the whole, the HME process improved the values of TPC, TFC, TEAC and IVPD in the extrudates compared to the raw extrusion mixtures. The addition of Spirulina along with controlled extrusion parameters can deliver meat analogues with improved physico-chemical and nutritional 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.