Acetaldehyde concentrations

EQ binary enzyme complex between Q acetaldehyde concentration (mM)... 

The results shown in Figure 5 confirm that benzaldehyde concentrations were maintained close to the desired value while pyruvate concentrations increased to approx. 200 mM presumably due to its slower conversion (than predicted) to acetoin and acetaldehyde. After 55 h a maximum PAC concentration of approx. 300 mM was reached, while acetoin and acetaldehyde concentrations were 20 mM and 5 mM, respectively. A residual PDC activity of 35% remained at this time. 

The computation result yield acetaldehyde concentration as function of time. The value of kinetics parameters, ki, ka, k3 were adjusted to minimize the sum of square of error between the predicted and measured concentration using Hooke Jeeve method [3]. 

We are repeating a discussion from Chapter 4, but here we emphasize that this is a chain reaction. This reaction is found experimentally to be irreversible and proportional to the power of the acetaldehyde concentration,... 

Measurements of acetaldehyde accumulation were reported in some of the earliest descriptions of the MOX process, where 5 months of MOX at 3 mL/L/month was found to raise the acetaldehyde concentration to 33 mg/L, compared to a control wine at 13 mg/L (Moutounet et ah, 1996). Further trials at Oenodev for a Syrah wine in 300-L tanks, and subject to elevated O2 delivery rates of 30,60, or 90 mL/L/month for 3 weeks, have shown that acetaldehyde will progressively accumulate to be perceived by a tasting panel from an early stage. Increased concentrations of acetaldehyde by GC were cordirmed for all treatments over the control by the end of the trial, with very high concentrations (50 mg/L) seen in the 90-mL/L/month MOX treatment (Oenodev, 2009). 

Throughout the course of MOX trials with commercial scale Monas-trell wines, the concentration of acetaldehyde was not found to increase over a 5-month period (Cano-Lopez et ah, 2006), even though more colored compounds involving acetaldehyde were found to form in the MOX wines (see below). However, in similar trials, the acetaldehyde concentration was higher with the MOX treatments after a final MOX phase at 3 mL/L/month post-MLF by up to an additional 13 mg/L both free and total SO2 were depleted in the MOX wines by the end of the trial (Cano-Lopez et ah, 2008). In these trials, the MOX operation was discontinued during MLF for a period of 1-2 months, on the expectation that the bacteria will consume the acetaldehyde produced during this period. 

FIGURE 4.6 Development of acetaldehyde concentrations during the microoxygenation of a Merlot wine for (A) a 141-L pilot plant study and (B) a 2400-L study. Reprinted with permission from Carlton et al. (2007). Copyright 2007 American Chemical Society. 

Carlton, W. K., Gump, B., Fugelsang, K., and Hasson, A. S. (2007). Monitoring acetaldehyde concentrations during micro-oxygenation of red wine by headspace solid-phase microextraction with on-fiber derivatization. /. Agric. Food Chem. 55,5620-5625. 

When these individuals drink alcohol, they develop high blood acetaldehyde concentrations and experience a flushing reaction similar to that seen with the combination of disulfiram and ethanol. Although the presence of the form of ALDH with reduced activity appears to protect against alcoholism, its presence in chronic alcoholism is associated with increased risk of severe liver disease, presumably owing to the toxic effects of acetaldehyde. 

All these reactions are endothermic and have high activation energies. The observation that acetaldehyde concentration rises during the pic darret while that of formaldehyde decreases suggests that only the last reaction is important and that formaldehyde is formed by oxidation (e.g., of CH3) rather than by pyrolysis. 

The relative importance of these reactions will be a complex function of oxygen, metal, ion and acetaldehyde concentrations. Moreover, the byproduct distribution will also depend on the stability of the intermediate products of Reaction 28 in each system. 

Most of the reactions produced some 2-methylpropanal in the products. Not shown in Tables 1-6 are yields of formaldehyde and acetaldehyde, which were not measured in these initial experiments. A subsequent experiment with the SOM carbon was performed with several cold traps to determine formaldehyde and acetaldehyde concentrations in the products. The results are discussed below. 

An assessment of the plausibility of various pathways that could introduce the organic compounds into precipitation suggests aqueous-phase oxidation of aldehydes is probably not a major contributor because of the large atmospheric acetaldehyde concentration that must be postulated to produce the observed formate/acetate ratio. Alternatively, potential gas-phase formic and acetic acid... 

Thus the gross differences in the rate laws for acetone and acetaldehyde condensation arise not from differences in reaction mechanism, but rather from differences in the relative rates of attack by enolate ion on reactant. In principle, at sufficiently low acetaldehyde concentrations, the rate law for the acetaldehyde should approach that for acetone. 

Storage in cellars at temperatures from 7 °C in winter to 17 °C in summer, and 60-80% relative humidity, for 6 years and 3 months. In this way, a yeast him develops on the surface of the wine that alters its sensory properties. Thus, the wine acquires a typical golden yellow colour and an acetaldehyde concentration of 600-700 mg/L (Pham et al. 1995). 

The restrictive conditions of the biological aging process of wine (namely low pH, presence of sulphite, high ethanol and acetaldehyde concentrations, lack of sugars and low oxygen concentration) are compatible with only a few S. cerevisiae races. Also, the presence of specific flor races has been correlated with the aging stage of the wine and the sensory features of the end product (Mesa et al. 2000). 

Factors affecting the reaction. The extent of the reactions between anthocyanins and pyruvic acid in model solutions follows a first order kinetic with respect to the anthocyanin disappearance. This reaction is affected by several factors, such as anthocyanin composition, pH, pyruvic acid concentration, temperature and acetaldehyde concentration. The maximum formation took place at pH 2.7-3.0 due to requirement of the anthocyanin fiavylium form, at high pyruvic acid concentration, at low storage temperature (10-15 °C) and in the absence of acetaldehyde (Romero and Bakker 1999a,b, 2000a,b). 

With regards to carbonyl compounds, acetaldehyde is the predominant aldehyde formed during fermentation most aldehydes produced, however, are formed independent of direct yeast action (29,30). Delteil and Jarry (57) found significant strain-specific production differences- , cerevisiae strain K1 producing 128 mg/L and S. cerevisiae strain D47 producing 105 mg/L Ough and Amerine (52) report average acetaldehyde concentrations in wines on the order of 54 mg/L. 

Aldehyde Levels in Different Varieties and Styles of Wine. The derivatization procedure described above was used to determine aldehyde levels in several different wines (Table 4). The wines were made in the UCD Department of Viticulture and Enology winery using standard procedures. As expected, acetaldehyde was the predominant aldehyde in all samples, with highest levels observed in the Sherry (Table 3). The acetaldehyde concentrations are consistent with those obtained by enzymatic analysis of acetaldehyde in table wines and Sherries (38). 

In fact, a recent study [9] of the effect of formaldehyde on the oxidation of acetaldehyde between about 120 and 190 °C has shown that the maximum rate is not a good rate parameter for the retarded reactions and the rate at 25% reaction (po.2s) was used. The effect of formaldehyde on po. 2 s is shown in Fig. 16. Small amounts of CH2O markedly retard the oxidation. At 188 °C, the plots of Po.25 versus the reciprocal of the initial formaldehyde concentration (F,) are linear (the gradients being proportional to the cube of the initial acetaldehyde concentration),... 

The combustion of ethanol has been studied between 270 and 370 °C by Cullis and Newitt [15—18]. At first, there is a period of some minutes during which no pressure change is discernible, although acetaldehyde is accumulating in the system [15]. When the acetaldehyde concentration reaches a critical level, the pressure begins to rise autocatalytically and methanol, formaldehyde and carbon monoxide become detectable [16]. 

Letort s investigations " threw new light on the question. He concluded that an order, n, can be deduced from the relationship between the initial rate and concentration, and a different one, n, from the change of the acetaldehyde concentration with time in any one experiment. He connected n with the inhibition caused by the reaction products. 

This is in accordance with the observations that the product distribution is practically independent of the acetaldehyde concentration and of the light intensity. Apparently, reaction (27) is significant only at high intensities. This step is the only reasonable explanation of the hydrogen formation under such circumstances. 

Increased acetaldehyde concentrations in the liver cell lead to severe morphological damage, especially in the mitochondria and the cytoskeleton, and to increased lipid peroxidations. 

FIGURE 4.72 Ptasma concentrations alcohoJ and related metabolites after a dose of alcohol. Human subjects received a doM of ethanol via a Sloma.ch tube (0.15 g of ethanol/kg body weight). Plasma conoentrptioris oi ethinoi ( ) acetaldehyde (O) and acetate (A) were measured at the indicated times. Acetaldehyde concentrations were one lhousandth those of ethanoln about 1.0 xM. (Redrawn with peirrussion from DiPadova eta., 1987.)... 

Problem 21.13 (a) When acetaldehyde at fairly high concentration was allowed to undergo base-catalyzed aldol condensation in heavy water (D2O), the product was found to contain almost no deuterium bound to carbon. This finding has been taken as one piece of evidence that the slow step in this aldol condensation is formation of the carbanion. How would you justify this conclusion (b) The kinetics also supports this conclusion. What kinetics would you expect if this were the case (Remember Two molecules of acetaldehyde are involved in aldol condensation.) (c) When the experiment in part (a) was carried out at low acetaldehyde concentration, the product was found to contain considerable deuterium bound to carbon. How do you account for this (Hint See Sec. 14.20.) (d) In contrast to acetaldehyde, acetone was found to undergo base-catalyzed hydrogen-deuterium exchange much faster than aldol condensation. What is one important factor contributing to this difference in behavior ... 

Inhalation exposure to acetaldehyde has produced nasal tumors in rats and laryngeal tumors in hamsters. Male and female rats were exposed to acetaldehyde 6hday , 5 day week for 28 months at concentrations of 0, 750, 1500, or 3000 ppm. A concentration-related incidence of squamous cell carcinomas of the respiratory epithelium was observed in both male and female rats. A statistically significant number of adenocarcinomas occurred in the olfactory epithelium of both sexes of rats exposed at all three acetaldehyde concentrations. Male and female hamsters were exposed to acetaldehyde 7hday, 5 day week at concentrations gradually reduced from 2500 to 1650 ppm for 52 weeks. Both sexes of acetaldehyde-exposed hamsters developed laryngeal tumors consisting of squamous cell carcinomas and adenosquamous cell carcinomas. 

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