Antioxidant capacity of phenolic compounds on human cell lines as affected by grape-tyrosinase and Botrytis-laccase oxidation.

Phenolic components (PCs) are well-known for their positive impact on human health. In addition to their action as radical scavengers, they act as activators for the intrinsic cellular antioxidant system. Polyphenol oxidases (PPOs) such as tyrosinase and laccase catalyze the enzymatic oxidation of PCs and thus, can alter their scavenging and antioxidative capacity. In this study, oxidation by tryosinase was shown to increase the antioxidant capacity of many PCs, especially those that lack adjacent aromatic hydroxyl groups. In contrast, oxidation by laccase tended to decrease the antioxidant capacity of red wine and distinct PCs. This was clearly demonstrated for p-coumaric acid and resveratrol, which is associated with many health benefits. While oxidation by tyrosinase increased their antioxidant activity laccase treatment resulted in a decreased activity and also of that for red wines.

Influence of Laccase and Tyrosinase on the Antioxidant Capacity of Selected Phenolic Compounds on Human Cell Lines.

Polyphenolic compounds affect the color, odor and taste of numerous food products of plant origin. In addition to the visual and gustatory properties, they serve as radical scavengers and have antioxidant effects. Polyphenols, especially resveratrol in red wine, have gained increasing scientific and public interest due to their presumptive beneficial impact on human health. Enzymatic oxidation of phenolic compounds takes place under the influence of polyphenol oxidases (PPO), including tyrosinase and laccase. Several studies have demonstrated the radical scavenger effect of plants, food products and individual polyphenols in vitro, but, apart from resveratrol, such impact has not been proved in physiological test systems. Furthermore, only a few data exist on the antioxidant capacities of the enzymatic oxidation products of phenolic compounds generated by PPO. We report here first results about the antioxidant effects of phenolic substances, before and after oxidation by fungal model tyrosinase and laccase. In general, the common chemical 2,2-diphenyl-1-picrylhydrazyl assay and the biological tests using two different types of cell cultures (monocytes and endothelial cells) delivered similar results. The phenols tested showed significant differences with respect to their antioxidant activity in all test systems. Their antioxidant capacities after enzymatic conversion decreased or increased depending on the individual PPO used.

The yeast Wickerhamomyces anomalus AS1 secretes a multifunctional exo-ß-1,3-glucanase with implications for winemaking.

A multifunctional exo-ß-1,3-glucanase (WaExg2) was purified from the culture supernatant of the yeast Wickerhamomyces anomalus AS1. The enzyme was identified by mass spectroscopic analysis of tryptic peptide fragments and the encoding gene WaEXG2 was sequenced. The latter codes for a protein of 427 amino acids, beginning with a probable signal peptide (17 aa) for secretion. The mature protein has a molecular mass of 47 456 Da with a calculated pI of 4.84. The somewhat higher mass of the protein in SDS-PAGE might be due to bound carbohydrates. Presumptive disulphide bridges confer a high compactness to the molecule. This explains the apparent smaller molecular mass (35 kDa) of the native enzyme determined by electrophoresis, whereas the unfolded form is consistent with the theoretical mass. Enzymatic hydrolysis of selected glycosides and glycans by WaExg2 was proved by TLC analysis of cleavage products. Glucose was detected as the sole hydrolysis product from laminarin, underlining that the enzyme acts as an exoglucanase. In addition, the enzyme efficiently hydrolysed small ß-linked glycosides (arbutin, esculin, polydatin, salicin) and disaccharides (cellobiose, gentiobiose). WaExg2 was active under typical wine-related conditions, such as low pH (3.5-4.0), high sugar concentrations (up to 20% w/v), high ethanol concentrations (10-15% v/v), presence of sulphites (up to 2 mm) and various cations. Therefore, the characterized enzyme might have multiple uses in winemaking, to increase concentrations of sensory and bioactive compounds by splitting glycosylated precursors or to reduce viscosity by hydrolysis of glycan slimes.