Unlocking the Potential Use of Protein From Pumpkin and Spinach Leaves for Dough Fortification: A Comprehensive Investigation Into Dough Rheology and Nutritional Benefits

In this study, the effects of spinach and pumpkin leaf proteins, as well as the addition of soy protein, on dough rheology were investigated. Changes in rheological properties were attributed to the distinct interactions of proteins, which differ in their functional characteristics—such as solubility and water/oil binding capacity, and structural features, including hydrophobicity and sulfhydryl group content. The dough water absorption capacity increased from 52.6 ± 0.21% to 57.6 ± 0.33%, 55.5 ± 0.42%, and 53.1 ± 0.12% when soybean, spinach, and pumpkin leaf proteins were incorporated into wheat flour at 5% w/w, respectively. In addition to improved water absorption, changes in dough development time, dough stability, viscosity, and the shelf life of the final product were observed as a result of the incorporation of these plant proteins. A higher content of free sulfhydryl groups observed in pumpkin (49.07 ± 1.03 µmol/g protein) and spinach leaf proteins (58.19 ± 0.49 µmol/g protein) was associated with a noticeable reduction in dough development time and stability compared to soy protein, where a considerably lower free sulfhydryl content (6.21 ± 0.21 µmol/g protein) was measured. The formation of a dough with higher mixing stability was attributed to hydrophobic interactions between soy proteins and similarly hydrophobic gluten. Significantly higher polyphenol content and biological activity were exhibited by dough enriched with pumpkin and spinach leaf proteins compared to dough made with wheat flour and fortified with soy protein. In addition, the essential amino acid profile of the enriched dough was notably improved through the addition of these plant-based proteins to wheat flour.