Effects of different carrageenan types on the rheological and water-holding properties of tofu

- The tofu with κ/ι-hybrid carrageenan had the highest rheological properties.
- The rheological properties of tofu were affected by the carrageenan type and concentration.
- Carrageenan could be a practical food additive to modify the texture of tofu.

Effects of three carrageenan types including κ/ι-hybrid carrageenan, κ/ι-mixture carrageenan, and K+-κ-carrageenan in the concentrations of 0.5 g/kg, 1.5 g/kg, 2.5 g/kg on the texture, rheological property, microstructure, and water holding property of tofu were compared for texture control. Types of carrageenan repeating units affected the coagulation process by changing the protein aggregation behavior in heated soymilk, resulting in the formation of tofu with distinct rheological and water-holding properties. The hardness and elasticity of tofu with κ/ι-hybrid carrageenan were higher. The addition of carrageenan increased the expressible water of tofu without varying its syneresis. The stress relaxation data suggested two relaxation mechanisms in tofu. One appears at a shorter time between 0.4 and 15 s for both λ1 and λ2 that represents the aqueous phase with buffering ability in the tofu matrix. The other shows at a longer time around 60-95 s (λ3), that represents the network frame structure in the matrix. The addition of carrageenan increased the λ3 of tofu, indicating the decrease of network chain mobility. Tofu became softer and less elastic when the concentration of carrageenan was increased. The above phenomenon might be due to the changes in the network structure of tofu by carrageenan.