Influence of pH on the Enzymic Oxidation of (+)-Catechin in Model Systems

Guyot, Sylvain; Cheynier, Véronique; Souquet, Jean‐Marc; Moutounet, Michel

doi:10.1021/jf00057a027

Cited by 86 publications

(67 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The colour of these products differed; they were colourless at pH <4 and yellow at high pH. Their interflavanic bonds also differed from the original monomer (Guyot et al, 1995;Monagas et al, 2005).…”

Section: Oxygen Addition In Must Enzymatic Oxidation and Hyperoxidationmentioning

confidence: 95%

Oxygen in Must and Wine: A review

Toit

Marais

Pretorius

et al. 2017

SAJEV

107

View full text Add to dashboard Cite

The atmosphere consists of approximately 21% oxygen (O2). It plays a crucial role in many metabolic and chemical reactions on earth, thus it is of little surprise that it plays a very important role in the winemaking process. Wine can never be completely protected from it. The general use of sulphur dioxide as an anti-oxidant dates back to the early 18th century and the protection of wine from unwanted oxidative spoilage has been recognised . Oxygen can influence the composition and quality of wine drastically, either positively or negatively, and this will be the focus of this review. This review will also focus on the basic steps involved in oxidation, substrates for oxidation in wine and the evolution of wine constituents during the wine production process when in contact with different concentrations of O2. Basic reactions of oxygen in wineOxidation is the process where electron transfer takes place between reductive and oxidative partners. In wine, O 2 is predominantly responsible for this, with it being reduced to certain intermediates and eventually to hydrogen peroxide and then water. Molecular O2 exists as a diradical and is thus in a triplet ground state. This limits the reactivity of O2 and it cannot form bonds by accepting electron pairs. However, the addition of a single electron, originating from reduced transitional metal ions, can overcome this limitation. This leads to an unpaired electron in the resulting negatively-charged superoxide radical, with a second electron transfer resulting in a peroxide anion (Miller et al., 1990;Danilewicz, 2003). This phenomenon results in O2 being involved in various reactions in wine. Substrates for oxidation in winePhenolic molecules originating from grapes can basically be divided into the non-flavonoids and the flavonoids. The nonflavonoids, which are hydroxybenzoic and hydroxycinnamic derivatives, originate from the grape juice, and are normally the principal phenolic molecules in white wines at concentrations ranging from 50-250 mg/L, depending on the cultivar, winemaking techniques, etc. Examples of non-flavonoids are the tartaric esters of caffeic acid, p-coutaric acid and furanic acids. These molecules have been shown to be the main phenolic molecules in white wine that did not receive prolonged periods of skin contact, because they occur at higher concentrations in the grape juice (Margalit, 1997;Monagas et al., 2005).The second main group of grape-derived phenolics is the flavonoids. This group of molecules basically consists of two phenolic rings attached to a pyran ring. The flavanoids have a more complex structure than the non-flavonoids. In a young wine they are normally in a more unpolymerised state, but as wine matures they undergo different polymerisation reactions in which O 2 plays an important role. The most important flavonoids in wine are the anthocyanins, flavanols and flavonols. Anthocyanins occur mainly in the skins of red grape cultivars and are responsible for the colour of red wine. In young red wines their concentrations can range fr...

show abstract

Section: Oxygen Addition In Must Enzymatic Oxidation and Hyperoxidationmentioning

confidence: 95%

Oxygen in Must and Wine: A review

Toit

Marais

Pretorius

et al. 2017

SAJEV

107

View full text Add to dashboard Cite

show abstract

“…At alkaline pH, 1,4 addition reactions to amine or thiolate nucleophiles are favored. However, at physiological pH these nucleophiles are for the most part protonated and unavailable for reaction, and quinones are more likely to undergo reverse disproportionation with phenols to form two equivalents of semiquinone radicals (Guyot et al 1995(Guyot et al , 1996. Semiquinone radicals may then react with a wide variety of targets through classical radical coupling mechanisms.…”

Section: Ppo Functionmentioning

confidence: 99%

Antisense downregulation of polyphenol oxidase results in enhanced disease susceptibility

Thipyapong

Hunt

Steffens

2004

Planta

203

129

View full text Add to dashboard Cite

Polyphenol oxidases (PPOs; EC 1.14.18.1 or EC 1.10.3.2) catalyze the oxidation of phenolics to quinones, highly reactive intermediates whose secondary reactions are responsible for much of the oxidative browning that accompanies plant senescence, wounding, and responses to pathogens. To assess the impact of PPO expression on resistance to Pseudomonas syringae pv. tomato we introduced a chimeric antisense potato PPO cDNA into tomato (Lycopersicon esculentum L.). Oxidation of caffeic acid, the dominant o-diphenolic aglycone of tomato foliage, was decreased ca. 40-fold by antisense expression of PPO. All members of the PPO gene family were downregulated: neither immunoreactive PPO nor PPO-specific mRNA were detectable in the transgenic plants. In addition, the antisense PPO construct suppressed inducible increases in PPO activity. Downregulation of PPO in antisense plants did not affect growth, development, or reproduction of greenhouse-grown plants. However, antisense PPO expression dramatically increased susceptibility to P. syringae expressing the avirulence gene avrPto in both Pto and pto backgrounds. In a compatible (pto) interaction, plants constitutively expressing an antisense PPO construct exhibited a 55-fold increase in bacterial growth, three times larger lesion area, and ten times more lesions cm(-2) than nontransformed plants. In an incompatible (Pto) interaction, antisense PPO plants exhibited 100-fold increases in bacterial growth and ten times more lesions cm(-2) than nontransformed plants. Although it is not clear whether hypersusceptibility of antisense plants is due to low constitutive PPO levels or failure to induce PPO upon infection, these findings suggest a critical role for PPO-catalyzed phenolic oxidation in limiting disease development. As a preliminary effort to understand the role of induced PPO in limiting disease development, we also examined the response of PPO promoter::beta-glucuronidase constructs when plants are challenged with P. syringae in both Pto and pto backgrounds. While PPO B inducibility was the same in both compatible and incompatible interactions, PPO D, E and F were induced to higher levels and with different expression patterns in incompatible interactions.

show abstract

“…4 and 5). As found in the literature, the pH value has a significant effect also on the course of the enzymatic oxidation of a similar compound (+)-catechin, from which colour products were formed mainly at a higher pH value [13].…”

Section: Výsledky a Diskusementioning

confidence: 52%

“…4 a 5). Podle literatury má pH význačný vliv také na průběh enzymové oxidace podobné látky (+)-katechinu, z níž vznikaly barevné produkty hlavně při vyšším pH [13].…”

Section: Výsledky a Diskuseunclassified

Colour changes during beer aging.

Šavel¹,

Košin²,

Brož³

2008

Kvasny Prum

View full text Add to dashboard Cite

Šavel, J. -Košin, P. -Brož, A.: Změny barvy při stárnutí piva. Kvasny Prum. 54, 2008, č. 2, s. 30-37. Studovaly se změny spekter žlutých, oranžových a žlutočervených oxidačních produktů epikatechinu s typickým absorpčním maximem v okolí 430 nm. K neenzymové tvorbě těchto látek je nutný kyslík, a jejich tvorba se zvyšuje s rostoucím pH a koncentrací kovů Fe 2+ a Cu 2+ . Z těchto důvodů vznikají barevné produkty snáze ve vodě vodovodní, než deionizované. Vzniklá barviva se mohou částečně odbarvovat s klesajícím pH a rostoucí koncentrací redukujících látek. Jednou vytvořené barevné látky nelze zcela vratně zredukovat, čemuž odpovídá model částečně vratné oxidačně-redukční reakce a postupné narůstání barvy modelových roztoků i piva v aerobním i anaerobním prostředí. Oxidované polyfenoly i reduktony mohou při redukci poskytovat další oxidační činidla, např. radikály semichinonů a reduktonů, jejichž vzájem-nými reakcemi nevratně vznikají další barevné produkty. Vzájemné reakce mezi oxidovanými polyfenoly a reduktony lze urychlit ozářením viditelným světlem a potom sledovat diferenční spektrofotometrií. Spectrum changes of yellow, orange and yellow-red oxidation products of epicatechin with their typical absorption maximum around 430 nm were studied. Oxygen is necessary for the non-enzymatic formation of these substances and their formation increases with growing pH value and Fe 2+ and Cu 2+ concentration. Based on the a.m. reasons, colour products are formed more easily in tap water than in deionized one. The colour substances formed can partially discolour with falling pH value and increasing concentration of reducing substances. Colour substances once formed cannot be fully reversibly reduced, which corresponds to the model of a partially reversible oxidation-reduction reaction and gradual colour increasing of model solutions as well as beer in both aerobic and anaerobic conditions.Oxidized polyphenols as well as reductones can provide further oxidizing agents during the reduction process, such as semiquinone and reductone radicals and further colour substances are formed as a result of their mutual reactions.Mutual reactions between oxidized polyphenols and reductones can be speeded up by the effect of visible radiation and then observed by differential spectrophotometry. Šavel ÚVODZměny barvy potravin při jejich skladování se vykládají různými mechanismy chemických přeměn. Obvykle se uvažují enzymová a neenzymová oxidace polyfenolů a/nebo vznik melanoidních látek [1]. Podobně se chová i pivo, které stárnutím hnědne za tvorby nežá-doucích chuťových produktů. V úvahu je nutné vzít vznik barevných karamelizačních látek, zejména při rmutování a vaření mladiny [2].Ačkoliv počáteční reakční mechanismus těchto reakcí je dobře znám, málo detailních informací se v literatuře získá o dalších stupních tvorby barevných produktů. U polyfenolů se nejčastěji uvádějí barevné oxidační produkty katechinů, u sacharidů karamelizační nebo melanoidní pigmenty.Enzymově i neenzymově oxidovaný katechin vykazuje typický absorpční pás ...

show abstract

Influence of pH on the Enzymic Oxidation of (+)-Catechin in Model Systems

Cited by 86 publications

References 17 publications

Oxygen in Must and Wine: A review

Oxygen in Must and Wine: A review

Antisense downregulation of polyphenol oxidase results in enhanced disease susceptibility

Colour changes during beer aging.

Contact Info

Product

Resources

About