In this study, Gynura procumbens was fermented in order to develop a new natural antioxidant and whitening agent. The non-fermented Gynura procumbens was used as the control, while fermentation was carried out by using Bacillus subtilis (BS), Lactobacillus casei (LC), Lactobacillus plantarum (LP), Candida utilis (CU), Saccharomyces cerevisiae 541 (S1) and Saccharomyces cerevisiae 1011 (S2). This study was investigated in order to evaluate the culture characteristics, substances, antioxidant activity, antimicrobial activity, and whitening activity of the fermented Gynura procumbens.

The pH of BS, LC, LP, CU, S1, and S2 were 5.56, 3.84, 3.69, 4.11, 4.12, and 4.14, respectively. The turbidity was 1.15~1.40, and the direct viable count was 5.38~6.92 log CFU/mL. The yield measurements of BS, LC, LP, CU, S1, and S2 were 18.12%, 14.52%, 14.31%, 14.15%, 14.08%, and 13.47%, respectively.

The total sugar of CU increased, and reducing the sugar of BS increased the result, as compared to the control. The amino acid composition of LP (except for isoleucine, tyrosine, cysteine, and methionine) was higher than that of the control. The total polyphenol contents of LC was 18.74 mg GAE/g, which was higher than that of the control.

As for the antioxidant activity experiment, DPPH and ABTS radical scavenging activity IC50 values of LC were 1.03 mg/mL and 2.01 mg/mL, respectively. The total flavonoid contents of LP was 1.69 mg CE/g. The FRAP value of LC was 139.40 mM/g. The antibacterial activity of LC and LP were the highest on B. cereus and higher than the control on E. coli and S. enterica.

In order to confirm the whitening effect, the inhibition of mushroom tyrosinase activity and melanin synthesis were measured. The LC fermentation product showed the strongest inhibition of tyrosinase activity and melanin synthesis.

Based on these results, it is suggested that the Lactobacillus casei fermentation product was an appropriate healthy food in terms of its antioxidant activity, antibacterial activity, and whitening activity.