# Effects of CaCO3/NaHCO3 on Porous Structure and Quality Characteristics of Protein–Starch Gel Network Formed via Extrusion

## TL;DR

This study explores how CaCO3 and NaHCO3 affect the structure and quality of protein-starch gels made through extrusion, showing how their combination influences expansion, hardness, and water retention.

## Contribution

The study reveals the combined effects of CaCO3 and NaHCO3 on the porous structure and quality of extruded protein–starch gels, offering new insights into their functional properties.

## Key findings

- Increasing NaHCO3 proportion significantly increased the expansion ratio and water holding capacity of the extrudate.
- Higher CaCO3 content led to a denser structure and reduced water holding capacity.
- A 0:2 CaCO3/NaHCO3 ratio resulted in the lowest hardness, and increased pH enhanced protein flexibility and gel elasticity.

## 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 (p < 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.