Casse oxidasic

L. Q. Chen, X.E. Zhang, W.H. Xie, Y.F. Zhou, Z.P. Zhang and A.E.G. Cass, Genetic modification of glucose oxidase for improving performance of an amperometric glucose biosensor, Biosens. Bioelectron., 17 (2002) 851-857. 

Enzyme biosensors have been described using a range of transduction elements (amper-ometry, potentiometry, optical and photo-thermal). The first biosensor was described in the literature by Clarck and Lyons (1962a) and was based on the use of glucose oxidase combined with electrochemical detection. Since then, this principle has been widely applied in biosensor development, and the enzyme systems used have been mainly oxido-reductases (e.g. tyrosinase, peroxidase and lactase) (Cass etal., 1984 Kulis and Vidziunaite, 2003), and hydrolases (choline esterases) (Andreescu etal., 2002 Nunes etal., 1998). 

This type of oxidized impression is not, however, considered acceptable in other types of wine, where freshness is an essential qnality. This chapter does not deal with oxidasic casse, which causes a very fast enzymic oxidation of many components in mnst and wine (Volume 1,... 

The reaction scheme used in the first commercial electrochemical test strip from MediSense (now Abbott Diabetes Care) is shown later. Electron transfer rates between the reduced form of glucose oxidase and ferricinium ion derivatives are very rapid compared with the unwanted side reaction with oxygen (Cass et al. 1984 Forrow et al. 2002). The Abbott Diabetes Care Precision QID strip includes the l,l -dimethyl-3-(2-amino-l-hydroxyethyl) ferrocene mediator, which has the desirable characteristics of high solubility in water, fast electron-shuttling (bimolecular rate constant of 4.3 X 10 M s ), stability, and pH independence of the redox potential (Heller and Feldman 2008). Electrochemical oxidation of the ferrocene derivative is performed at 0.6 V. Oxidation of interferences, such as ascorbic acid and acetaminophen present in blood, are corrected for by measuring the current at a second electrode on the strip that does not contain glucose oxidase. 

Antioxidasic it instantaneously inhibits the functioning of oxidation enzymes (tyrosinase, laccase) and can ensure their destruction over time. Before fermentation, SO2 protects musts from oxidation by this mechanism. It also helps to avoid oxidasic casse in white and red wines made from rotten grapes. 

Total phenolic compounds (index) Color intensity Oxidasic casse potential... 

Rot is responsible for the most serious oxidative phenomena. In fact, Botrytis cinerea secretes a laccase more active and stable than the tyrosinase of grapes. It is responsible for the oxidasic casse in red wines derived from rotten grapes. An appropriate sulfiting can protect against this phenomenon... 

An effective protection can be obtained in red wines sensitive to oxidasic casse as well as white musts during winemaking. At present, however, the use of ascorbic acid is not widespread in winemaking and not authorized in France probably because the required concentrations are too high to protect musts against oxidations and because sulfur dioxide is more effective. 

Aeration can be harmful. In partially rotted grapes, it can provoke an oxidasic casse. 

With botrytized grapes, stems protect wine color from oxidasic casse. The laccase activity of Botrytis cinerea is most likely fixated or inhibited. 

A cool year or cool climate is characterized by a late and often insufficient maturity. Grape acidity is elevated and the musts are thus relatively protected against bacterial attack. However, there is a risk of botrytis attacks and the formation of oxidasic casse, since cool climates often correspond to rainy climates. In addition, grape crops arriving at the winery are often characterized by relatively low temperatures in cool years. As a result, the initiation of fermentation can be difficult, even more so when the grapes are washed by rain the natural yeast inoculation can be insufficient. 

The must should therefore be warmed as quickly as possible to 20°C. If the fermentation does not begin shortly after warming, the temperature rapidly drops down to its initial value. A simultaneous yeast inoculation is required to avoid this problem it also accelerates the fermentation and thus provokes a more considerable temperature increase. If the temperature becomes too elevated, cooling may be required after these operations which accelerate the fermentation. Aeration also remains useful, as long as the harvest is not susceptible to oxidasic casse. 

With rotten grapes, snlfiting does not improve the extraction of pigments instead, it prevents the laccase activity of Bolrylis cinerea from destroying them. The numbers in Table 12.8 show that high sulfur dioxide concentrations increase the total phenolic compound concentration and color intensity in the case of highly contaminated grapes. The elevated tint value in the control sample is due to a yellow component, characteristic of oxidasic casse. 

Table 12.11. Laccase destruction (expressed in arbitrary units) and oxidasic casse protection according to sulfiting (free-run wine) (Dubemet, 1974)...

Certain measures should be taken when wines made from rotten grapes are run off. First of all, sntfur dioxide has a high combination rate in these wines. The sntfur dioxide concentrations must therefore be relatively high (5 g/hf or more). In the presence of SO2, enzymatic activity is instantly inhibited, but the complete destruction of laccase activity is slow. At concentrations of 20-30 mg of free SO2 per liter, several days are required to destroy this enzyme completely. Fortunately, during this time, the sulfur dioxide protects the wine against oxidasic casse. After the complete... 

Figure 12.10 indicates the role of sulfiting in protecting against oxidasic casse in wine. The wine contains laccase and is exposed to air. Figure 12.10a corresponds to the aeration of a non-sulfited sample. The laccase activity diminishes according to time but does not disappear. In the first phase, the red color component (OD 520) and the yellow color component (OD 420) increase. In the second phase, the oxidasic casse appears with an increase in the yellow color component and a decrease in the red color component. In phase 3, the oxidasic casse causes a precipitation of colored matter. 

Figure 12.10c indicates the evolution of the same wine exposed to air, after sulfiting at 55 mg/1. When the free SO2 concentration falls to zero after 48 hours, the laccase activity has been completely destroyed. The wine is thus definitively protected from oxidasic casse. The yellow color component and especially the red color component increase with exposure to air. 

VDN are subject to the same clarification and stabilization problems as other wines. Iron casse, proteic casse, tartrate deposits and colored matter can cloud the wines. Standard preventive measmes can help to avoid these problems. Oxidasic casse is another accident linked to grape rot. 

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