Nutritional, Phytochemical, and In Vitro Antioxidant Activity Analysis of Different States of Soy Products

Consumer demand for food nutritional content and quality is driving the design of plant-based foods that are enhanced with proteins. In this study, we aimed to reveal the nutrient compositional differences of various states of soy flours. We compared soy protein concentrate (SPC) with full fat (FF), raw soy flour (RSF), and defatted (DF) soy flour for investigating nutritional content, phytochemicals, and in vitro antioxidant activity. The results showed that the SPC contained significantly (p < 0.001) higher protein content (65.14%) and low-fat content (0.54%) than RSF, FF, and DF. Furthermore, the findings revealed that all products contain a significant (ANOVA, p < 0.001) amount of essential minerals. The RSF contains significantly higher (p < 0.001) potassium (1178.6 mg), calcium (216.77 mg), and magnesium (247 mg) per 100 g than FF, DF, and SPC. SPC contains essential amino acids, but we were unable to detect phenylalanine and tryptophan due to a limitation in the method. Furthermore, using methanolic and aqueous extracts of RSF, FF, DF, and SPC, the flavonoid, phenolics, and antioxidant capacity were also evaluated. According to the findings, soy products in methanolic extract had higher phenolic (about 12-34 mg/g) and flavonoid (about 63-150 mg/g) levels than aqueous extract. Results also demonstrated that FF had higher phenolic content, and SPC had higher flavonoid content than the other products. In vitro models such as phosphomolybdenum blue, FRAP, DPPH, and ABTS assays were used to study the total antioxidant and free radical scavenging potential of soy products, and results found that soy products contained a significant (p < 0.001) amount of antioxidant equivalent to gallic acid and vitamin C standard. In the DPPH and ABTS assays, the results also showed that soy products can reduce free radicals in different in vitro models. Altogether, these findings suggest that soy flours, particularly DF and SPC, could be a beneficial food ingredient in the formulation of functional foods.