Effect of Rice Protein, Zein and Their Hydrolysates on the Properties of Wheat Dough

In order to investigate the effects of exogenous proteins and their hydrolysates on the properties of wheat dough, different percentages (4% and 8%) of rice protein (RP), zein, rice protein hydrolysate (RPH), and zein hydrolysate (ZH) were added to wheat dough, and their effects on the mixing properties, pasting properties, thermodynamic properties, rheological properties and gluten network structure of wheat dough were investigated. The results showed that adding 4% or 8% of RP and zein increased the water absorption of wheat dough, whereas the additions of RPH and ZH induced significant decreases in the water absorption of wheat dough. Meanwhile, the additions of RPH and ZH resulted in significant reductions in the dough stabilization time, C3 value, and C5~C4 value when compared with proteins (RP, zein) (P<0.05), indicating protein hydrolysates were more effective than proteins to inhibit the formation of gluten network and starch retrogradation in dough. The results of pasting and thermal properties showed that adding proteins and their hydrolysates significantly decreased the peak viscosity, valley viscosity, final viscosity, and gelatinization temperature of starch (P<0.05). The effects of hydrolysates on the pasting and thermal properties were more significant than proteins (P<0.05). Rheological properties analysis showed that the addition of 4% or 8% zein increased the G' values, while the addition of RP, RPH, and ZH decreased the G' values of doughs. Meanwhile, adding 4% or 8% RP increased the G'' values, while adding zein, RPH, and ZH decreased the G'' values of the doughs. SEM results showed that the addition of RP and RPH disrupted the gluten network of wheat dough, with RPH causing more significant damage to the gluten network. Adding 4% zein improved the gluten network of the wheat dough, but 8% ZH disrupted the gluten network in doughs. Furthermore, SDS-PAGE showed that proteins and their hydrolysates influenced protein aggregation and gluten network formation. In summary, adding RP to the dough disrupted the gluten network in the dough, whereas moderate amounts of zein (4%) improved the gluten network, and adding 8% of zein had a detrimental effect. Compared with proteins (RP, zein), protein hydrolysates (RPH, ZH) were more effective in disrupting the formation of gluten network in dough and inhibiting the retrogradation of starch after pasting. This study provides some theoretical guidance for the development of gluten-reducing and anti-aging additives.