Abstract
Tofu has a long history of use and is rich in high-quality plant protein; however, its production process is relatively complicated. The tofu production process includes soybean pretreatment, soaking, grinding, boiling, pulping, pressing, and packing. Every step in this process has an impact on the soy protein and, ultimately, affects the quality of the tofu. Furthermore, soy protein gel is the basis for the formation of soy curd. This review summarizes the series of changes in the composition and structure of soy protein that occur during the processing of tofu (specifically, during the pressing, preservation, and packaging steps) and the effects of soybean varieties, storage conditions, soybean milk pretreatment, and coagulant types on the structure of soybean protein and the quality of tofu. Finally, we highlight the advantages and limitations of current research and provide directions for future research in tofu production. This review is aimed at providing a reference for research into and improvement of the production of tofu.
Highlights
Tofu originated in the time of the Western Han dynasty and has been consumed for more than two thousand years
The 7S conglycinin and 11S glycinin are the key components of tofu curd, accounting for more than 70% of the total soy protein content [11]. 7S conglycinin is a trimer composed of an α subunit, α subunit, and β subunit and accounts for approximately 30% of the soy protein content [12]. 11S glycinin is a hexamer composed of acidic polypeptides (A) and basic polypeptides (B) linked by disulfide bonds and accounts for approximately 40% of the soy protein content
The network structure of whole bean curd is mostly irregular, discontinuous, large, and uneven. This is because some insoluble dietary fiber particles are embedded in the network structure, which destroys the continuity of the soy protein gel network [37]
Summary
Tofu originated in the time of the Western Han dynasty and has been consumed for more than two thousand years. Soy Protein Soy is composed of approximately 40% proteins, 20% lipids, 25% carbohydrates, and 5% crude fibers [2,4] They are rich sources of isoflavones, minerals, and other components. 11S glycinin is a hexamer composed of acidic polypeptides (A) and basic polypeptides (B) linked by disulfide bonds and accounts for approximately 40% of the soy protein content. Soy protein undergoes dissociation or association reactions during the acid-base treatment and heat treatment, which changes the ionic strength of the solution. Through these association– dissociation reactions, 11S glycinin polymerizes to form dimers, oligomers, or multimers or dissociates to form 7S and 3S components [14]
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