Kinetics of Tyrosinase Inhibition, Antioxidant Activity, Total Flavonoid Content and Analysis of Averrhoa bilimbi L. Extracts and its Fruit Vinegar Using FTIR and Multivariate Methods

Melanin is a natural substance responsible for human skin pigmentation. Tyrosinase is known as a key enzyme involved in melanin production; therefore, hyperactivity of this enzyme leads to hyperpigmentation in human. In current study, leaves and fruits of Averrhoa bilimbi L. were extracted with ethanol and water solvents, and its fruit vinegar was produced by fermenting fresh fruits with sugar at room temperature for 10 days. The leaf and aqueous extracts of A. bilimbi L. and its fruit vinegar were investigated for tyrosinase inhibitory activity using L-DOPA as substrates, antioxidant activity using 2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation decolorization assay and total flavonoid content (TFC) using aluminium chloride colorimetric method.  Moreover, kinetic study of anti-tyrosinase activity of A. bilimbi extracts and its fruit vinegar, including Fourier transform infrared (FTIR) spectra and principal component analysis (PCA) were carried out. The result indicated ethanol extracts from A. bilimbi fruits and leaves showed the highest TFC and anti-tyrosinase activity, whereas aqueous extracts of its fruits and leaves showed the highest radical scavenging activity. Interestingly, the result revealed the existence of TFC, radical scavenging activity and anti-tyrosinase activity in the vinegar sample. The anti-tyrosinase potential of the fruit and leaf ethanol extracts of A. bilimbi was identified as an uncompetitive inhibitor (Km= 0.54 and 0.51 µM, Vmax= 0.0173 and 0.0146 O.D.450/min, respectively). Positive correlation was significantly found between radical scavenging activity and TFC, between anti-tyrosinase activity and TFC, between FTIR data and TFC, and between FTIR data and anti-tyrosinase activity, (r = 0.83, 0.56, 0.66, 0.75; p-value < 0.05, respectively). Therefore, the extracts and fruit vinegar of A. bilimbi L. could be considered as natural source of an anti-tyrosinase compounds for cosmetics and healthy foods.
HIGHLIGHTS

The ethanol extracts and fruit vinegar showed high flavonoid content, antioxidant activity and anti-tyrosinase activity
The anti-tryrosinase potential was identified as an uncompetitive inhibitor
Positive correlation was significantly found between chemical and biological data
FTIR, PCA and cluster analysis showed differentiation between extracts and its fruit vinegar

GRAPHICAL ABSTRACT