Wine Chemistry and Biochemistry

236 M. Luz Sanz and Isabel Mart ́ınez-Castro

COOH

H OH

HO H

H OH

H OH

CH 2 OH

CHO

H OH

HO H

H OH

H OH

COOH

Gluconic acid Glucuronic acid

O

O

OH

OH

OH

CH 2 OH

delta-Gluconolactone

Fig. 7.6Structures of gluconic acid, glucuronic acid and delta-gluconolactone

in position 6 of the chain is oxidized, the compound formed is a uronic acid

(Fig. 7.6).

Aldonic acids are in equilibrium with their lactones, formed by reversible esterifi-

cation of the carboxyl group with a hydroxyl in 4 or 5 position (gamma and delta

lactones) (e.g. delta-gluconolactone; Fig. 7.6).
Both ends of an aldose chain can be simultaneously oxidized to carboxylic acids

forming aldaric acids (e.g. galactose to galactaric acid; Fig. 7.7).

• Reduction: the carbonyl group of an aldose can be reduced with sodium boro-

hydride to give a polyalcohol (alditol) with formula HOCH 2 (CHOH)nCH 2 OH.

When a keto group is reduced, two isomeric alditols are formed (e.g. whereas

glucose is reduced to glucitol, fructose gives a mixture of glucitol and mannitol;

Fig. 7.8).

Fig. 7.7Structures of
galactose and galactaric acid

CHO

H OH

HO H

HO H

H OH

CH 2 OH

Galactose

COOH

H OH

HO H

HO H

H OH

COOH

Galactaric acid