This report presents first evidence of managing wine flavor evolution during oxidation (including aging), by altering the reactions of quinones. O-quinone of 4-methylcatechol has been produced in acetonitrile by periodate resin. Michael addition reactions of o-quinone 4-methylcatechol to various nucleophiles, including varietal volatile thiols, hydrogen sulfide, glutathione, sulfur dioxide, ascorbic acid and amino acids like methionine and phenylalanine have been carried out, obtaining alkylated adducts in fairly good to quantitative yields. The reaction rate and selectivity of o-quinone 4-methylcatechol toward the studied nucleophiles have been investigated by UV-Vis spectrometry by following the loss of quinone chromophore. The observed reactivity spans 3 orders of magnitude on passing from amino acid (methionine and phenylalanine) (KNu = 0.0002 s-1) to the most reactive nucleophiles, the hydrogen sulfide (KNu = 0.4188 s-1). These are the first direct reaction rate measurements of nucleophilic addition to the oxidized catechol. The classification of the studied nucleophiles revealed the existence of three categories. The first group consisted of amino acids (methionine and phenylalanine) having rates of essentially zero. Next, phloroglucinol, has a very low rate (K = 0.0064). Despite the slow rate of this reaction, this data suggests phenolics may be able provide a protection for varietal thiol aroma under some circumstances. The next group of compounds includes the volatile thiols having increasing reactions rates K as steric inhibition declines. The tertiary thiol, 4MSP, was much less reactive with quinones than the secondary (3SH) and primary thiols (2FMT), and quite close to the rate of phloroglucinol. The odoriferous volatile thiols (4MSP, 3SH, 2FMT) showed lower K values than those of the third group of the wines antioxidant compounds (SO2, GSH, AA) and H2S. The result indicates that both the antioxidant compounds (SO2, GSH, AA) and H2S would react preferentially with oxidation induced quinones, resulting the preservation of varietal aromas. The characterization of the reaction products between the studied nucleophiles and ortho-quinones derived 4-methylcatechol, was performed by using HPLC-MS analyse. Three o-quinone 4-methylcatechol/H2S; phloroglucinol adducts, two o-quinone 4-methylcatechol/3SH; 2FMT; 4MSP adducts, and one o-quinone 4-methylcatechol/SO2 were detected. No adduct was detected into the reaction medium where o-quinone 4-methylcatechol was incubated with both methionine and phenylalanine explaining why there observed reaction rates were essentially zero. Competition experiments provided strong support to involvement of antioxidants such as such as SO2, glutathione and ascorbic acid should to the preservation of wine?s varietal flavors.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF2011-10-15 14:39:362017-10-15 14:40:30Oxidation of Wine: Control for Quality