BIOTRANSFORMATION EFFECTS ON ANTIOXIDANT ACTIVITIES OF WHITE GRAPE POMACE

Introduction: Food bioactive phenolic compounds have received attention due to their possible beneficial health effects. These chemical compounds present hydroxyl and aromatic rings, possibly related to their antioxidant power. Grapes and grapes residues are rich sources of phenolic compounds, and consequently, good antioxidants, which may inhibit or reduce damages caused by the deleterious action of free radicals. Studies indicate that enzymatic biotransformations, including with the enzyme tannase (tannin acyl hydrolase), may improve the bioavailability and bioactivity of phenolic compounds through the hydrolysis of compounds.

Objectives: The objective of this work was to compare the antioxidant effects of extracts produced from white grape pomace (GP), before and after biotransformation with tannase.

Methods: GP was obtained from a Rio Grande do Sul state, Brazil, and comprised skins, seeds and stems from Moscato branco variety. The total phenolic content was determined by Folin-Ciocalteau colorimetric method. The antioxidant activity was determined by the scavenging of DPPH (2,2-diphenyl-1-picrylhydrazyl) radical, by oxygen radical absorption capacity (ORAC) and by the evaluation of intracellular reactive oxygen species (ROS) using the pre-adipocyte 3T3-L1 cell line. The non-citotoxic concentration of samples used (200 μg/mL) was determined by sulforhodamine assay. The effects of GP treatments on the generation of ROS in 3T3-L1 cells were evaluated by using dichlorodihydrofluorescein probe (H2DCFDA), while 2.2’-Azobis(2-amidinopropane) dihydrocloride (AAPH) was used to induce ROS formation.

Results and discussion: The biotransformed grape pomace extract (BGPE) presented an increase of 184% in total phenolics, compared to non-biotransformed grape pomace extract (GPE). In DPPH and ORAC assays, BGPE showed enhancements of 42% and 27% in the antioxidant values, respectively. These results indicate that tannase assisted to extract more phenolic compounds from the residue, therefore increased the antioxidant power and the phenolic total content of the extract. AAPH alone enhanced ROS production by 503% compared to negative control after 5h. When cells were treated with AAPH and GP extracts simultaneously, the ROS production was decreased to 63 and 53.9% for GPE and BGPE, respectively. That is, the extracts have a protector effect against the ROS production in cells.

Conclusion: The enzymatic biotransformation by tannase enhanced the extraction of phenolic bioactive compounds, showing positive effects on the antioxidant activity of GP. These results support the valuation of agroindustrial waste and show the importance of using biotechnogical process to positive modify biological properties of grape residues.

Acknowledgements: The authors acknowledge the financial support received from CNPq.