Tyrosinase Inhibitory Activity of Crude Procyanidin Extract from Green Soybean Seed and the Stability of Bioactive Compounds in an Anti-Aging Skin Care Formulation

Green soybean (Glycine max L.) seed contains a high procyanidin content and high antioxidant activity. Moreover, ultrasound-assisted extraction (UAE) has proved to be advantageous in providing high extraction efficiency. Hence, this study aimed to extract procyanidins from green soybean seeds (GSSs) using UAE. This study also evaluated the inhibitory activities of tyrosinase and the cytotoxic effects of crude procyanidin extract. The extract exhibited maximum levels of bioactive components and antioxidant capacity when subjected to a temperature of 15 °C and an extraction time of 20 min. The crude procyanidin extract at a concentration of 10 mg/mL inhibited the tyrosinase enzyme by more than 60%, and the half-maximal inhibitory concentration (IC₅₀) value obtained for the extract was 6.85 ± 0.81 mg/mL. This result was much greater than the IC₅₀ value obtained for kojic acid (0.089 ± 0.08 mg/mL), which was used as a positive control. For the cytotoxicity assessment, the results indicated that the crude procyanidin extract showed no cytotoxicity and actually stimulated the growth of human skin fibroblast cells. More than 80% of the bioactive compounds (total phenolic content (TPC), total flavonoid content (TFC), procyanidin content (PC)) and antioxidant activities (DPPH and FRAP) of the crude extract powder were retained at 38.68 ± 0.01 mg GAE/g, 16.07 ± 0.01 mg CAE/g, 9.24 ± 0.01 mg PC/g, 359.8 ± 0.72 μM Trolox eq/g, and 1640 ± 2.86 μM Trolox eq/g, respectively, after 12 weeks of storage at 25 °C. The crude procyanidin extract powder was then included in a facial serum formulation and tested for pH value and physical evaluation. The stability of the crude procyanidin extract facial serum was shown to be greater for bioactive compounds and antioxidant activity when stored at a temperature of 4 °C than when stored at a temperature of 25 °C. These results suggest that the GSS extracts obtained via ultrasonication show promise for use in cosmeceutical formulations for whitening skincare products.