Influence of the Degree of Hydrolysis on Functional Properties and Antioxidant Activity of Enzymatic Soybean Protein Hydrolysates

Abstract

Soybean protein hydrolysates were prepared using two proteolytic enzymes (Alcalase and Protamex) and the degree of hydrolysis (DH) and their functional and antioxidant properties were evaluated. The highest DH value was 20%, with a yield of 19.77% and protein content of 51.64%. The total amino acid content was more than 41% for all protein hydrolysates. The protein hydrolysates from Protamex at pH 2.0 had excellent solubility, emulsifying activity, and foaming capacity, at 83.83%, 95.03 m²/g, and 93.84%, respectively. The water-holding capacity was 4.52 g/g for Alcalase, and the oil-holding capacity was 4.91 g/g for Protamex. The antioxidant activity (62.07%), as measured by the samples' reaction with DPPH (2,2-diphenyl-1-picrylhydrazyl) and the reducing power (0.27) were the strongest for Protamex. An ABTS activity rate of 70.21% was recorded for Alcalase. These findings indicated a strong potential for the utilization of soybean protein hydrolysates to improve the functional properties and antioxidant activity of soybeans as well as their nutritional values.

Keywords: antioxidant activity; degree of hydrolysis; enzymatic hydrolysis; functional properties; soybean protein hydrolysate.

Figure 1

Effects of different conditions on degree of hydrolysis: (a) enzyme-to-substrate ratio, (b) sample-to-buffer ratio (S/L), and (c) time of incubation. Data are expressed as mean ± S.D. for n = 3. Different small letters within each assay indicate significant differences (p < 0.05).

Figure 2

Functional properties of soybean protein hydrolysate: (a) protein solubility (%), (b) emulsifying activity index (m²/g), (c) foaming capacity (%), and (d) water- and oil-holding capacity (g/g). The values represent means of three independent experiments ± SD. Different characters indicates significant differences at each pH (p < 0.05).

Figure 3

Comparison of antioxidant activities of soybean protein hydrolysates at different DH: (a) DPPH free radical scavenging activity (%), (b) ABTS free radical scavenging activity (%), and (c) reducing power capacity at 700 nm. Values are mean ± SD. Different small characters indicate significant differences (p < 0.05).