Impact of Citric Acid on the Texture and Microstructure of Thermally Induced Tofu‐Like Gels From Soy, Chickpea, and Mung Bean Protein Isolates

Citric acid-induced gelation influences the texture of tofu-like gels prepared from plant protein isolates. This study investigated the effects of 0.1% citric acid addition on the texture and microstructural properties of tofu-like gels prepared from soy protein isolate (SPI), chickpea protein isolate (CPI), and mung bean protein isolate (MPI). Texture analysis and puncture tests revealed significant changes. The hardness (g) of the three isolates significantly decreased (SPI from 348.42 to 184.91 g; CPI from 254.38 to 134.41 g; MPI from 181.94 to 82.92 g; P < 0.05). The breaking strength (N/m²) also decreased from 23.71 to 21.42 N/m² for SPI, from 20.93 to 19.44 N/m² for CPI, and from 15.48 to 13.35 N/m² for MPI. Scanning electron microscopy revealed the following microstructural changes: SPI transformed from a uniform tofu-like matrix with a large interstitial gel network to a denser, more ordered network with smaller pores; CPI transformed from a loose structure with dense globules to larger precipitated flocs without network formation; and MPI transformed from fibrous clusters with loose, regular droplets to an irregular, nonuniform, and porous crystalline structure. These findings suggest that citric acid can influence the texture and microstructure of plant protein isolates, rendering the gel softer and more fragile than in its original state without citric acid addition. This study lays the foundation for further investigation of tofu-like gels from different protein sources and highlights the potential for innovative food design by manipulating texture and microstructure using citric acid.