Lactic acid dissociation

Anaerobic glycolysis results in acid production in the form of H. Glycolysis forms pyruvic acid, which is reduced to lactic acid. At an intracellular pH of 7.35, lactic acid dissociates to form the carboxylate anion, lactate, and H (the pKa for lactic acid is 3.85). Lactate and the H are both transported out of the cell into interstitial fluid by a transporter on the plasma membrane and eventually diffuse into the blood. If the amount of lactate generated exceeds the buffering capacity of the blood, the pH drops below the normal range, resulting in lac-ticacidosis (see Chapter 4). 

Since Na has no acid-base properties and H2O is a weak acid or base, the pH will be controlled by the lactic acid dissociation equilibrium ... 

What is true for acetic acid is also true for other carboxylic acids at the ph ysiological pH that exists inside cells, carboxylic acids are almost entirely dissociated. To reflect this fact, we always refer to cellular carboxylic acids by the name of their anion—acetate, lactate, citrate, and so forth, rather than acetic acid, lactic acid, and citric acid. 

The answer is D. Weak acids like lactic acid never completely dissociate in solution and are thus defined by the property that at least some of the protonated (undissociated acid) form and the unprotonated (conjugate base) form of the acid are present at all concentrations and pH conditions. The indicated of 5.2 is consistent with the idea that the lactate anion retains a strong affinity for protons, a hallmark of a weak acid. The lactate anion is highly water-soluble. All weak acids obey the Henderson-Hasselbalch equation. 

Commercial casein is usually manufactured from skim milk by precipitating the casein through acidification or rennet coagulation. Casein exists in milk as a calcium caseinate-calcium phosphate complex. When acid is added, the complex is dissociated, and at pH 4.6, the isoelectric point of casein, maximum precipitation occurs. Relatively little commercial casein is produced in the United States, but imports amounted to well over 150 million lb in 1981 (USDA 1981C). Casein is widely used in food products as a protein supplement. Industrial uses include paper coatings, glues, plastics and artificial fibers. Casein is typed according to the process used to precipitate it from milk, such as hydrochloric acid casein, sulfuric acid casein, lactic acid casein, coprecipitated casein, rennet casein, and low-viscosity casein. Differences... 

PROBLEM 13.3 Lactic acid, which builds up in muscle tissue upon strenuous exercise, is partially dissociated in aqueous solution ... 

P a negative logarithm of the acid dissociation constant PLA poly(lactic acid)... 

Lactic acid (HC3H5O3) is a waste product that accumulates in muscle tissue during exertion, leading to pain and a feeling of fatigue. In a 0.100 M aqueous solution, lactic acid is 3.7% dissociated. Calculate the value of Ka for this acid. 

Of the two major weak organic acids produced by LAB (acetic and lactic acid), acetic acid is the strongest inhibitor because of its higher dissociation constant (pKa = 4.75) as compared to lactic acid (pKa = 3.08) at a given molar concentration and pH level (Eklund, 1983 Holzapfel et al., 1995 Ouwehand, 1998). 

Fig. 4-10. Separation of organic acids on IonPac ICE-AS5. - Eluent 0.0016 mol/L perfluorobu-tyric acid flow rate 0.3 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations fully dissociated compounds (1), 10 ppm oxalic acid (2), 25 ppm pyruvic acid (3), and tartaric acid (4), 30 ppm malonic acid (5), lactic acid (6), malic acid (7), and acetic acid (8), 20 ppm isodtric acid (9), 30 ppm citric acid (10), 40 ppm / -hydroxybutyric acid (11), succinic acid (12), and propionic acid (13).

Feed with formic and propionic acids has been found to reduce Salmonella colonization in broilers (Thomson and Hinton, 1997), whereas decontamination of chicken carcasses with acetic or lactic acid reduced Campylobacter on carcasses or meat (Van Netten et al., 1994 Chaveerach et al., 2002). Organic acids, when added to feeds, should be protected to avoid dissociation in the crop and in the intestine that are known to possess higher pH and to reach far into the GIT, where the targeted bacterial population is situated (Gauthier, 2005). 

Two cotransporters that are activated at low pH help maintain the cytosolic pH In animal cells very close to 7.4 despite metabolic production of carbonic and lactic acids. One, a Na /H antiporter, exports excess protons. The other, a Na HCOs /CP cotransporter, imports HCOs , which dissociates in the cytosol to yield pH-raising OH ions. 

The transport of hydrogen ions out of the cell is also important for maintenance of a constant intracellular pH. Metabolism produces a number of other acids in addition to CO2. For example, the metabolic acids acetoacetic acid and (3-hydroxybutyric acid are produced from fatty acid oxidation to ketone bodies in the liver, and lactic acid is produced by glycolysis in muscle and other tissues. The pKa for most metabolic carboxylic acids is below 5, so these acids are completely dissociated at the pH of blood and cellular fluid. Metabolic anions are transported out of the cell together with H (see Fig. 4.9, circle 8). If the cell becomes too acidic, more H is transported out in exchange for Na ions by a different transporter. If the cell becomes too alkaline, more bicarbonate is transported out in exchange for Cl ions. 

Salicylate, which is a degradation product of aspirin in the human, is lipid soluble and has a dissociable proton. In high concentrations, as in salicylate poisoning, salicylate is able to partially uncouple mitochondria. The decline of ATP concentration in the cell and consequent increase of AMP in the cytosol stimulates glycolysis. The overstimulation of the glycolytic pathway (see Chapter 22) results in increased levels of lactic acid in the blood and a metabolic acidosis. Fortunately, Dennis Veere did not develop this consequence of aspirin poisoning (see Chapter 4). 

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