Transforming microalgal Chlorella biomass into cosmetically and nutraceutically protein hydrolysates using high-efficiency enzymatic hydrolysis approach

This study aimed to produce the cosmetically and nutraceutically protein hydrolysates derived from alkaline-soluble proteins of microalgal Chlorella biomass via Alcalase enzymatic hydrolysis approach. Protein hydrolysates having high degree of hydrolysis and bioactivities were obtained after response surface methodology (RSM) optimization under optimized conditions: pH of 6.5, 60 °C of reaction temperature, 3 h of hydrolysis, and 3% enzyme-to-substrate loading. Under optimum conditions, the Alcalase enzyme exhibited a high efficiency of cleaving peptide bonds within proteins by increased free amino groups in protein hydrolysates > 1.50-fold as compared to the unhydrolyzed protein. Antioxidative properties including DPPH radical scavenging activity and ferric-reducing antioxidant power (FRAP) ability were also increased with the IC 50 values of 0.16 and 0.58 mg protein/mL, respectively. Interestingly, protein hydrolysates showed a high-efficiency inhibition effect on tyrosinase activity using L-DOPA and L-tyrosine as substrates in melanogenesis with the IC 50 recorded at 0.99 and 0.41 mg protein/mL, respectively. Inhibitory kinetic studies confirmed that these protein hydrolysates demonstrated mixed inhibition of DPPH, FRAP, and tyrosinase enzyme when L-tyrosine was used as substrate and also exhibited an uncompetitive inhibition to tyrosinase enzyme when using L-DOPA substrate. SDS-PAGE proved that the molecular weight of protein hydrolysates was ≤ 2 kDa. More importantly, the presences of essential amino acids (> 62 g/100 g protein) were satisfactory according to amino acid requirements in human nutrients with the WHO/FAO/UNU standard. Therefore, this study highlighted that protein hydrolysates derived enzymatically from microalgal biomass could be potentially used as natural bioactive ingredient in cosmetic and/or nutraceutical applications.