Chemical Properties
Colorless to light yellow liquid
Chemical Properties
Pyruvic acid has a sour, acetic odor (similar to acetic acid). It has a pleasant, sour taste with a burning, somewhat sweet note. It tends to darken and decompose unless kept free of minor contaminants and in tightly sealed containers
Occurrence
Isolated from cane sugar fermentation broth and from a few plants; also reported found in peppermint, raw asparagus, leaves and stalk of celery, onion, rutabaga, milk, cream, buttermilk, wheaten bread, blue cheeses, cheddar cheese, cottage cheese, provolone cheese, yogurt, beef, Virginia tobacco, beer, white wine, botrytised wine, cocoa and sake.
Preparation
By distillation of tartaric acid in the presence of potassium acid sulfate as a dehydrating agent; from acetyl chloride and potassium cyanide to yield the nitrile, which is subsequently acid hydrolyzed to the acid; pyruvic acid must be rectified under vacuum.
Aroma threshold values
Aroma characteristics at 1.0%: acidic, sweet, caramellic and sour.
Taste threshold values
Taste characteristics at 5 ppm: sharp acidic, sour fruity, with sour creamy and caramellic nuances.
General Description
Pyruvic acid is the key component formed during the hydrolysis of flavor-precursors called S-alk(en)yl-L-cysteine-sulfoxides in onion tissues by allinase during maceration or chopping. The amount of pyruvic acid formed is used as a measure for onion pungency.
Biochem/physiol Actions
Taste at 5 ppm
Biotechnological Applications
Pyruvic acid is a key position in cell metabolism and is involved in many catabolic and anabolic pathways, including glycolysis, gluconeogenesis, amino acid, and protein metabolism. Pyruvic acid is employed for the production of L-tryptophan, L-tyrosine, and 3,4-dihydroxyphenyl alanine in various industries. The diet supplementation with pyruvic acid increased fat loss and minimized the associated loss of body protein. Pyruvic acid is also used in biochemical researches and medicine as a substrate for assaying activities of such enzymes as pyruvate dehydrogenase, pyruvate carboxylase, and pyruvate decarboxylase (Nakazawa et al. 1972; Yamada et al. 1972; Stanko et al. 1992).
Y. lipolytica oxidize glucose and form pyruvic acid (75–80 %) and a-ketoglutaric acid (20–25 %) under thiamine deficiency conditions. The synthesis of the acid was triggered by a decrease in intracellular thiamine concentration to 3.0 lg per 1 g biomass. An approximately 3-fold increase in the amount of the biomass was associated with a subsequent decrease in thiamine content to the level of 1.0 lg per 1 g biomass, whose maximum production of pyruvic acid was 50 g/L in this condition. In addition to glucose, thiamine-auxotrophic yeasts are capable of synthesizing pyruvic acid when grown on glycerol and propionic acid. Technicalgrade glycerol is the most promising raw material for pyruvic acid production. Pyruvic acid was obtained at a concentration of 61 g/L with a yield of 71 % from glycerol (Morgunov et al. 2004; Finogenova et al. 2005).
Synthesis
Pyruvic acid's synthesis method is as follows: from Tartaric acid by heating with hydrophilic agents, such as Potassium hydrosulfate.
Purification Methods
Distil it twice, then fractionally crystallise it by partial freezing. [Beilstein 3 IV 1505.]
