Protein isolate was prepared from dark red kidney bean and was subjected to hydrolysis by two different proteases pepsin and papain by separate experiments. The antioxidant and antimicrobial properties of the resulting hydrolysates were evaluated by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay and agar diffusion method, respectively. The resulting pepsin hydrolysate DPH-1 exhibited the highest antioxidant activity with an IC50 of 0.015 ± 0.004 mg/mL compared to protein isolate DPI (0.115 ± 0.023 mg/mL) and papain hydrolysate DPH-2 (0.066 ± 0.014 mg/mL). Hydrolysis resulted in the significant (p < 0.05) increase of total polyphenol content in DPH-1 (38.39 mg GAE/g ± 1.17) and DPPH radical scavenging activity was significantly (p < 0.05) higher in both DPH-1 and DPH-2 than that of DPI. Also, DPH-1 showed better performance in terms of antioxidant activities in comparison to ascorbic acid, but the activity of DPH-1 increased significantly (p < 0.05) at 0.016 mg/mL. Moreover, both DPH-1 and DPH-2 delayed the formation of oxidizing substances when applied in apple juice stored for 6 days at room temperature. However, DPH-1 significantly (p < 0.05) retarded the oxidizing substances compared to control. Besides, DPH-1 exerted an antibacterial action against Escherichia coli with the diameter of the zone of inhibition (DIZ) of 20.26 mm and DPH-2 inhibited Pseudomonas aeruginosa with the DIZ of 19.23 mm. Overall, the results indicate that the dark red kidney bean protein hydrolysates thus obtained may be used as promising antioxidants or food additives.
