Lactones gluconic acid

Colourless crystals m.p. I25°C, soluble in water and alcohol. In aqueous solution forms equilibrium with its lactones. Gluconic acid is made by the oxidation of glucose by halogens, by electrolysis, by various moulds or by bacteria of the Acetobacter groups. 

Note D-Gluconic acid and other aldonic acids exist in equilibrium with lactone structures. 

The ability of bacteria - particularly Pseudomonas spp. and Glucottobader spp. - to produce gluconolactone and gluconic acid has been exploited and the process is used commerdally, mainly in the production of the lactone. 

Precipitation of Fe(IIl) compounds from acid solutions as the pH increases above 2.2 is a particular problem. Complexing agents that have been used include 5-sulfosalicylic acid and citric acid (136) dihydroxymaleic acid (137) ethylenediaminetetraacetic acid (138) lactic acid (138) blends of hydroxylamine hydrochloride, citric acid, and glucono-delta-lactone (139) nitriloacetic acid blends of citric acid and acetic acid lactic acid and gluconic acid (140). 

Problem 22.27 Fischer prepared L-gulose by oxidizing o-glucose to two separable lactones of glucaric acid. These were reduced to lactones of gluconic acid, which were further reduced. Give all the structures in these... 

S-lactone (Note 1) is added slowly with vigorous stirring. During the addition, the temperature should be kept below 65°. After an hour in the ice bath, the solution is kept at room temperature for 24 hours and is then poured into 1 1. of water and stirred until the hydrolysis of the acetic anhydride is complete (about an hour). The mixture is placed in a refrigerator until the product crystallizes completely (Note 2). The crude material is removed by filtration and washed with a small amount of ice water. The 2,3,4,6-tetra-O-acetyl-D-gluconic acid monohydrate thus obtained melts at 113-117°. The yield is 79-84 g. (74-79%). 

Lactobionic acid. This derivative is produced by oxidation of the free carbonyl group of lactose (Figure 2.25), chemically (Pt, Pd or Bi), electro-lytically, enzymatically or by fermentation. Its lactone crystallizes readily. Lactobionic acid has found only limited application its lactone could be used as an acidogen but it is probably not cost-competitive with gluconic acid-<5-lactone. It is used in preservation solutions for organs prior to transplants. 

Glucose oxidase (GO) catalyses the oxidation of glucose to gluconic acid (via gluconic acid-<5-lactone) according to the following reaction ... 

Adjustment of pH (e.g. by gluconic acid-<5-lactone) Removal or killing of contaminating bacteria Thermization (e.g. 65°C x 15 s)... 

The pH and the concentration of calcium in milk also vary, with consequential effects on the properties of renneted milk gels. The addition of CaCl2 to cheesemilk (0.02%) is widely practised and adjustment and standardization of milk pH by using the acidogen, gluconic acid-5-lactone (GDL), is recommended and commercially practised on a limited scale. 

Acid production is a key feature in the manufacture of all cheese varieties -the pH decreases to about 5 ( 0.3, depending on variety) within 5-20h, at a rate depending on the variety (Figure 10.11). Acidification is normally achieved via the bacterial fermentation of lactose to lactic acid, although an acidogen, usually gluconic acid-<5-lactone, alone or in combination with acid, may be used in some cases, e.g. Mozzarella. 

On acidification to pH 4.6, the caseins coagulate, which is the principle used to manufacture of a family of cheeses which represent about 25% of total cheese consumption and are the principal cheeses in some countries (Appendix 10B). Acidification is traditionally and usually achieved by in situ fermentation of lactose by a Lactococcus starter but direct acidification by acid or acidogen (gluconic acid-d-lactone) is also practised. The principal... 

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