Physicochemical, functional and nutritional properties of vegetables proteins and a novel mixture of soybean-maize as ingredients for application in foods

Abstract

Vegetable proteins are an excellent alternative to cope with the high demand for protein worldwide due to their low cost, availability and good nutritional value. In this study, the interactions between the physicochemical parameters and the functional properties of twenty vegetable proteins were determined to facilitate their incorporation into food processes. Likewise, the physicochemical parameters, functional and nutritional properties of isolated and hydrolyzed soybean proteins were compared with isolated and hydrolyzed proteins of a new mixture of soybean-maize to offer the consumer a new protein alternative of high nutritional value and useful functionality. Finally, the most suitable conditions for the hydrolysis of the soybean-maize protein were determined in terms of solubility to modify its functional properties and allow better integration in beverages. Through this study, it was determined that the pH, electrical conductivity (EC), urease activity (UA) and free alpha-amino nitrogen (FAAN) influenced the functional properties related to the protein-water interactions corresponding to the water solubility index (WSI), nitrogen solubility index (NSI), foaming activity (FA), foam stability (FS), heat coagulation capacity (HCC) and emulsion stability (ES). Likewise, it was observed that the content of soluble solids, which includes reducing sugars (RS), determined the performance of the fat absorption index (FAI), emulsifying activity index (EAI) and foam density (FD) of the twenty vegetable proteins. On the other hand, the comparison of the physicochemical, functional and nutritional properties of the isolated and hydrolyzed soybean proteins with those of soybean-maize allowed us to determine that the isolate and hydrolysate of the soybean and maize mixture had better functional properties than their analogs of soybeans since they had 10% and 52% more solubility, 47,385.01 (m2/g) and 12,071.87 (m2/g) more emulsifying capacity, 4.5% and 4.2% more foam density and 36, 3% and 1.2% more coagulation capacity, respectively. Besides, the soybean-maize protein mixture had 2.5% and 20.0% more isoleucine and tyrosine, respectively. At the same time, the electrophoretic profile of the protein mixture showed four additional bands to the typical pattern of soybeans with a molecular weight of 56, 55, 52 and 18 kDa, which could correspond to globulins and β-zein from maize, respectively. Regarding the study of enzymatic hydrolysis of soybean-maize protein, it was determined that the most suitable conditions for its hydrolysis were to use neutrase as the catalyst at a concentration of 0.45%, with a hydrolysis time of 30 minutes, at a pH 6.5 and a temperature of 45 °C. Under these hydrolysis conditions, it was determined that the hydrolyzed protein dispersion had free amino nitrogen of 5.03 mg/g, a solubility of 49.99% and a viscosity of 9.6 cP. The hydrolysis process increased the solubility of the soybean-maize protein by 34.33% compared to the unhydrolyzed sample. Therefore, soybean-maize protein has higher functionality than soybean protein, increasing the possibilities of being used in the food industry and taking advantage of its nutritional value and unit cost advantages.