The Effects of Die Temperature and Screw Speed on Extruded Pulse Flours and Their Application in Bread Production

Abstract

Extrusion is an innovative technology for improving the techno-functional and nutritional properties of pulse flours. This study aimed to optimize extrusion conditions for broad bean and mung bean flours and to assess their potential in bread making. Die temperature (135°C-165°C) and screw speed (200-300 rpm) were optimized using response surface methodology, with water absorption index (WAI), phytic acid (PA), and insoluble dietary fiber (ISDF) as response variables. Optimal conditions were found to be a 165°C die temperature and a 200 rpm screw speed for both pulses. Die temperature and screw speed had a significant effect on WAI, PA, and ISDF values. Flours obtained under optimum conditions showed the following changes: in mung bean, WAI increased by 50%, whereas PA and ISDF decreased by 59.5% and 30.9%, respectively; in faba bean, WAI increased by 33.69%, whereas PA and ISDF decreased by 45.27% and 29.68%, respectively. Extrusion disrupted starch crystallinity and changed protein-carbohydrate structures as observed by XRD, FTIR, and DSC analyses. Incorporation of pulse flours affected the rheological properties of the bread dough, causing a decrease in viscous and elastic responses. In bread making trials, wheat flour was substituted with pulse flours at 12.5% and 25%. Both substitution levels reduced bread volume and increased crumb hardness. In conclusion, it is shown that extrusion is an effective method for modifying the functional properties of pulse flours, and the use of optimized extrusion as a tool to develop novel functional pulse-based ingredients.

Keywords: bread; broad bean flour; extrusion; mung bean flour.

FIGURE 1

3D surface plots expressing the effect of die temperature and screw speed on (a) water absorption index, (b) phytic acid, (c) insoluble dietary fiber of extruded mung bean flour.

FIGURE 2

3D surface plots expressing the effect of die temperature and screw speed on (a) Water absorption index, (b) Phytic acid, (c) Insoluble dietary fiber of extruded broad bean flour.

FIGURE 3

The X‐ray diffraction (XRD) spectra of the flour samples. EBF, extruded broad bean flour; EMF, extruded mung bean flour; RBF, raw broad bean flour; RMF, raw mung bean flour; WF, wheat flour.

FIGURE 4

The FTIR spectra of flours. EBF, extruded broad bean flour; EMF, extruded mung bean flour; RBF, raw broad bean flour; RMF, Raw mung bean flour; WF, wheat flour.

FIGURE 5

Storage modulus (G′, solid markers) and loss modulus (G″, open markers) of samples during frequency sweep tests. Different marker shapes and colors correspond to the sample formulations indicated in the legend. 12.5‐EBB, bread dough prepared with 12.5% extruded broad bean flour‐87.5% wheat flour; 12.5‐EMB, bread dough prepared with 12.5% extruded mung bean flour‐87.5% wheat flour; 12.5‐RBB, bread dough prepared with 12.5% raw broad bean flour‐87.5% wheat flour; 12.5‐RMB, bread dough prepared with 12.5% raw mung bean flour‐87.5% wheat flour; 25‐EBB, bread dough prepared with 25% extruded broad bean flour‐75% wheat flour; 25‐EMB, bread dough prepared with 25% extruded mung bean flour‐75% wheat flour; 25‐RBB, bread dough prepared with 25% raw broad bean flour‐75% wheat flour; 25‐RMB, bread dough prepared with 25% raw mung bean flour‐75% wheat flour; WB‐C, bread dough prepared with wheat flour (control).

FIGURE 6

Cross‐section views of bread samples. 12.5‐EBB, 12.5% extruded broad bean flour‐87.5% wheat flour bread; 12.5‐EMB, 12.5% extruded mung bean flour‐87.5% wheat flour bread; 12.5‐RBB, 12.5% raw broad bean flour‐87.5% wheat flour bread; 12.5‐RMB, 12.5% raw mung bean flour‐87.5% wheat flour bread; 25‐EBB, 25% extruded broad bean flour‐75% wheat flour bread; 25‐EMB, 25% extruded mung bean flour‐75% wheat flour bread; 25‐RBB, 25% raw broad bean flour‐75% wheat flour bread; 25‐RMB, 25% raw mung bean flour‐75% wheat flour bread; WB‐C, wheat flour bread (control bread).

FIGURE 7

The morphological structures of breads. (a) WF‐C, (b) 12.5‐RMB, (c) 25‐RMB, (d) 12.5‐EMB, (e) 25‐EMB. 12.5‐EMB, 12.5% extruded mung bean flour‐87.5% wheat flour bread; 12.5‐RMB, 12.5% raw mung bean flour‐87.5% wheat flour bread; 25‐EMB, 25% extruded mung bean flour‐75% wheat flour bread; 25‐RMB, 25% raw mung bean flour‐75% wheat flour bread; WB‐C, wheat flour bread (control bread).

FIGURE 8

The morphological structures of breads. (a) WF‐C, (b) 12.5‐RBB, (c) 25‐RBB, (d) 12.5‐E‐BB, (e) 25‐EBB. WB‐C; Wheat flour bread (control bread). 12.5‐EBB, 12.5% extruded broad bean flour‐87.5% wheat flour bread; 12.5‐RBB, 12.5% raw broad bean flour‐87.5% wheat flour bread; 25‐EBB, 25% extruded broad bean flour‐75% wheat flour bread; 25‐RBB, 25% raw broad bean flour‐75% wheat flour bread.