Effects of CaCO<sub>3</sub>/NaHCO<sub>3</sub> on Porous Structure and Quality Characteristics of Protein-Starch Gel Network Formed via Extrusion.

Abstract

CaCO₃ and NaHCO₃, respectively serving as chemical leavening agents, can promote the expansion of protein or starch extrudates, thereby forming a porous structure. However, the characteristics of this porous structure under the combined regulation of CaCO₃ and NaHCO₃ remained unclear. The results indicated that increasing the proportion of NaHCO₃ promoted the expansion of the extruded protein-starch gel network, with its expansion ratio significantly increasing from 2.29 to 3.17 (<i>p</i> < 0.05). This expansion resulted in larger pores, which corroborated the observed significant increase in water holding capacity (WHC). Conversely, an increase in the proportion of CaCO₃ led to a denser porous structure accompanied by a reduction in WHC. Meanwhile, the extrudate with a CaCO₃/NaHCO₃ ratio of 0:2 exhibited the lowest hardness, measuring 8.87 N. As the proportion of NaHCO₃ increased, the pH shifted toward the alkaline range. This increase in pH enhanced the flexibility of the protein structure, leading to a significant rise in the proportion of disordered structures in the protein secondary structure, such as random coil and β-sheet, which facilitated the formation of an elastic gel network. In conclusion, both CaCO₃ and NaHCO₃ significantly modulated the porous structure of the protein-starch gel network formed during extrusion. This provides a new perspective for investigating the relationship between the protein-starch gel network and the quality characteristics of extruded products.