Pigments, phenolic compounds oxidation

A crnde extract of sweet potato Ipomoea-batatas (L.) Lam.) was nsed as a source of phenol oxidases (polyphenoloxidase, tyrosinase, catecholoxidase, EC 1.14.18.1). The extract was directly placed in the carrier of a FIA system with UVD, to promote oxidation of phenolic compounds to o-quinones that condense to form melanin-like pigments with a strong absorption at 410 nm. The determination of phenols in industrial wastewaters showed good agreement with conventional methods (correlation coefficient 0.9954) LOD was 10 p,M, with RSD <2.7% (w = 6). Under optimal storage conditions the enzymatic activity did not vary for at least five months . 

Other studies have described similar results to those found in our research, that is, that ellagitannins are more abundant in French oak (26) and therefore, in wines matured in French oak barrels. So, the presence of ellagitannins enhances the color of wine and increases absorbance at 620 nm by fevoring anthocyanin-procyanidin type tannin condensations with acetaldehyde (purple pigments) and that foct also helps to explain the higher PVPP index values of wines fix)m new French oak barrels. They also prevent the development of brick-yellow color by preventing the oxidation of phenolic compounds (24). 

In lettuce, raised CO2 atmospheres may cause a disorder called brown stain (browning of the epidermal tissue). This is caused by the production of brown pigments generated by the oxidation of phenolic compounds in the presence of the enzyme polyphenol oxidase. It was reported that under high CO2 atmospheres, PAL activity was induced whereas phenolic production and browning were inhibited until the lettuce was transferred from CO2 to air [164 165]. After this transfer, tissue browning occurred, which was associated with a rapid increase in the soluble phenolics content. 

Alessandra Napolitano graduated in chemistry in 1984 at the University of Naples Federico II under the guidance of Prof. G. Prota. In 2001 she was made associate professor of organic chemistry. Her main research interests lie in the field of heterocyclic compounds, with special reference to hydroxyindoles and benzothiazines, oxidative chemistry of phenolic natural products, food chemistry, lipid peroxidation, and analytical chemistry. Currently, she is involved in several research projects dealing with the chemistry of natural pigments, including pheomelanins, and the chemical basis of diseases. 

---