Malic acid concentrations 358

Coumarins unsubstituted in the heterocyclic ring may be obtained by using 2-hydroxy-butanedioic acid (malic acid). Concentrated sulfuric acid decomposes this acid with loss of carbon monoxide and water to formylacetic acid, which is of course a 1,3-dicarbonyl compound and reacts as such with the phenol (Scheme 111). It is sometimes advantageous to use a mixture of sulfuric and acetic acids, which reduces the extent of formation of tarry material. 

This research group applied the same approach to another red wine type, Rioja (Lopez-Rituerto et ah, 2009). In this study, PCA, performed on the entire fermentation time course of 207 days, demonstrated increases in ethanol, succinic, lactic, and acetic acids, while the alanine and malic acid concentrations decreased. Metabolite changes occurring during alcoholic fermentation were evaluated by performing PCA of the first 7 days of the... 

Several organic acids are also found in maple sap (Table 4.3). In general, the total quantity of organic acids starts out low, and rises throughout the sap flow season. Malic acid (concentration 800M5,000 ppb) is by far the most common organic acid, ranging from just over 50-99% of the total acid present. Succinic acid and oxalic acid are also fairly dominant forms. Other acids occur sporadically in low concentration (Dumont, 1994 Mollica and Morselli, 1984). 

Also the rate at which malic acid is removed from the cytoplasm by transport into the vacuoles should decrease at low temperatures because the flux of malic acid into the vacuole is assumed to be an active process (see Chap.4.2.3.2). Hence, relatively high cytoplasmic malic acid concentration would result which should inhibit PEP carboxylase thus lowering CO2 consumption. 

It is not known if the CO2 output rhythms described above are accompanied by corresponding oscillations in malic acid concentrations. Clearly, such acid changes would occur if the rhythmic phenomena were CAM-related. Since CO2-free air inhibits malic acid accumulation even in normal day/night cycles (Wolf, 1960 Kluge, 1968 b), the rhythmic phenomena described by Wilkins may not be CAM-related. However, Queiroz (1975) reported a circadian CO2 output rhythm by Kalanchoe blossfeldiana in normal air in darkness as did Wilkins (1959) with B.fedtschenkoi. Hence, the rhythms are probably not the result of the C02-free air, but since we do not know more about corresponding malic acid fluctuations, we cannot determine the extent to which the rhythmic CO2 output is CAM related. 

In Kalanchoe tubiflora, during the first cycle the CO2 uptake rhythm in continuous light and normal air is accompanied by a predictable oscillation in malic acid (Kluge, 1969 c). The malic acid concentration increases with CO2 uptake and decreases during the low CO2 uptake period. In Bryophyllum calycinum, Kress in Kluge s laboratory (unpublished) showed that the rhythm of CO2 uptake and... 

When grapes do not reach complete maturity in northern vineyards, grape acidity can be considerable. In these conditions, malic acid concentrations are almost always greater than those of tartaric acid. When the biological degradation of malic acid is not desired due to the organoleptical changes that it causes, the juice must be chemically... 

When there is too much surplus malic acid in the initial must, part of the calcium carbonate added to the treated volume produces soluble calcium malate. At the time of final blending, the surplus calcium reacts with the tartaric acid of the untreated must. The deacidification thus occurs in two steps and acts essentially on the tartaric acid. The tartaric acid concentration therefore has to be adjusted in order to decrease malic acid concentrations substantially, by double salt formation (Usseglio-Tomasset and Bosia, 1992). This result can be obtained by using a mixture of calcium carbonate and calcium tartrate, also... 

At the end of alcoholic fermentation, malic acid concentrations should be determined and monitored if necessary. Malolactic fermentation (MLF) normally occurs after the complete depletion of sugars. An early initiation of MLF is generally linked to alcoholic fermentation difficulties and insufficient sulfiting. In certain cases, the two fermentations take place simultaneously, even though the antagonistic phenomena between yeasts and bacteria tend to inhibit alcoholic fermentation. 

Malolactic fermentation is both relatively simple and extremely important in practice, and all sensible winemaking and red wine storage techniques take its existence and laws into account. It is an important element in premium wines, even in complete maturity years. In addition, it regulates wine quality from year to year. The less ripe the grapes and therefore the higher the malic acid concentration, the more malolactic fermentation lowers wine acidity. The differences in acidity of wines from the same region are much smaller than those of the corresponding musts. 

The decrease in acidity following malolactic fermentation varies according to the malic acid concentration and thus grape maturity. This decrease in acidity can be from 2 g/1 in H2SO4 to sometimes 3 g/1 (3-4.5 g/1 in tartaric acid). Total acidity decrease from 4.5-6.S g/1 in H2SO4 (6.75-9.75 g/1 in tartaric acid) to 3-4 g/1 H2SO4 (4.5-6 g/1 in tartaric acid). The fermentation of 1 g of malic acid per liter lowers the total acidity by approximately 0.4 g/1 in H2SO4 (0.6 g/1 in tartaric acid). 

The taste of the wine is also considerably improved. The role of deacidification becomes more important when the initial malic acid concentration of wine increases. The softening of wine is due first of all to a decrease in acidity. The substitution of the malic ion by the lactic ion also contributes. In fact, malic acid corresponds to the aggressive, green acid of unripe apples. Lactic acid is the acid found in milk it has a much less aggressive taste. Additionally, the association of the flavor of malic acid with the astringency of tannins is not harmonious. This phenomenon permits red wines to lose their acid and hard character. They become softer, fuller and fatter—essential elements for a quality wine. 

Alcohol is the first limiting factor of malolactic fermentation. Malic acid concentrations often decrease fastest in tanks containing the lowest alcohol concentrations. Leuconostoc oenos (now known as Oenococcus oeni) is predominantly responsible for malolactic fermentation in red wines and it cannot grow in alcohol concentrations exceeding 14% volume. Some lactobacilli can resist 18-20% volume alcohol and are apt to cause spoilage in fortified wines. Besides alcohol production, the wine yeast strain responsible for alcoholic fermentation affects bacterial growth and malolactic fermentation. It yields macromolecules (polysaccharides and proteins) to the medium. The enzymatic systems of the bacterial cell wall hydrolyze these substances. 

When the pH is excessively low, wine can be deacidified to facilitate the initiation of malolactic fermentation for example, 50 g of CaCOs per hectoliter can be added to the wine (Chapter 11). The role of this deacidification is to rectify the pH without removing an excessive amount of tartaric acid. This operation must take into account the decrease in total acidity brought about by malolactic fermentation, according to the malic acid concentration in the wine. This operation should be effected on a fraction of the total volume (20-30%, for example). This deacidified fraction is used to initiate the natural deacidification reactions (malolactic fermentation followed by potassium hydrogentartrate precipitation). 

L-malic acid is decarboxylated to L-lactic acid by LAB, a reaction known as MLF. Wine pH increases by several tenths of units depending on the initial malic acid concentration, which may range from 1 to 8 g/1. Although the MLF reaction has been known for a long time (Seifert 1901) only since the 1970s has the malolactic enzyme been purified and characterized, first from Lact. plcmtarum... 

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