Effect of soy protein hydrolysates incorporation on dough rheology, protein characteristic, noodle quality, and their correlations.

Soy protein hydrolysates (SPHs) have bioactive and nutritional functions that can be used as fortifier of noodles. The objective of this study is to explore the effect of SPHs on dough rheology and noodle quality. Two kinds of SPHs, with a hydrolysis degree of 4.43% (SPH4) and 7.47% (SPH7), were added to wheat flour at a ratio of 5:95 to make dough and noodles. The addition of SPHs decreased the gluten yield, gluten index, peak viscosity, final viscosity, and setback of flour paste. Dough stability decreased, but the extensibility increased because of the addition of SPHs. SPHs decreased the high molecular weight glutenin subunits and SDS-unextractable polymeric protein proportion, and the results of scanning electron microscopy and atomic force microscopy also showed that the gluten network in SPH7 dough was more discontinuous than that in SPH4, suggesting a stronger negative effect of SPH7 on the formation of the gluten network compared to that of SPH4. The incorporation of SPHs decreased the hardness and springiness of cooked noodles but increased their cooking loss, protein loss, and water absorption. The correlation analysis showed that high molecular weight subunits and SDS-unextractable polymeric protein in SPH-fortified dough were positively correlated with the hardness, adhesiveness, springiness, cohesiveness, chewiness, resilience, force, and distance at break of noodles, and these texture properties of noodles were positively correlated with pasting, gluten, and farinographical properties of SPH-fortified flour. These results suggested that SPHs could improve some qualities of noodles, such as smoothness and cooking yield, and resist pasted starch aging. PRACTICAL APPLICATION: Soy protein hydrolysates have many bioactive functions. This study demonstrated the feasibility of incorporating soy protein hydrolysates into wheat flour to prepare noodles. The addition of soy protein hydrolysates gives noodles smoother mouthfeel and increases the cooking yield. The addition of soy protein hydrolysates decreases the setback value of flour paste, suggesting that soy protein hydrolysates may help to resist starch aging, which is favorable for starch-containing foods such as precooked noodles. Thus, soy protein hydrolysates possess potential applications in noodle products.