Effects of Sulfur Dioxide on Food Quality - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 268

TABLE 8.3
Dissociation Constants K of Carbonyl-
S(IV) Adducts (Hydroxysulfonates)

Carbonyl Compound K /mmol l -1

Glucose 900

Fructose 15000

Arabinose 40

2-Ketoglutaric acid 0.5 (pH 3)-0.7 (pH 4)

Pyruvic acid 0.14 (pH 3)-0.22 (pH 4)

L-xylosone 1.4

D-Threo-2,5-hexodiulose 3.4

2,5-Diketogluconic acid 0.4

Galacturonic acid 17

Acetaldehyde 0.002

The value of K was calculated from the total carbonyl
and S(IV) species concentrations in solution. Unless
otherwise indicated, values are nominally for the pH
range 3 to 4.

Sources of the data are Burroughs, L. F. and Sparks,
A. H., J. Sci. Food Agric ., 24, 187, 1973; Würdig, F.
W. and Schlotter, H.-A., Wein Wiss ., 24, 67, 1969;
Beech, F. W., Burroughs, L. F., Timberlake, C. F., and
Whiting, G. C., Bull. O.I.V ., 586, 1001, 1979.

and pyruvic acids are formed in normal yeast fermentation, the yields being depen-
dent on fermentation time, the extent of aeration, the type of yeast, and the presence
of thiamin. The mechanisms for the production of these compounds are well under-
stood. Pyruvic acid is the final product of glycolysis. 2-Ketoglutaric acid is an
intermediate in the tricarboxylic acid cycle while acetaldehyde is formed as a result
of the decarboxylation of pyruvate. Increased acetaldehyde production is associated
with a reduction in pyruvate formation. 2-Ketoglutaric acid may also be formed
from 2,5-diketogluconic acid by Acetobacter melanogenum . Diacetyl and acetoin
are metabolic products of lactic acid bacteria. The ketogluconic acids (2-ketoglu-
conic, 5-ketogluconic, and 2,5-diketogluconic) are the result of the action of glu-
conobacter and pseudomonas on glucose and gluconic acid. Chromobacteria also
metabolize gluconic acid to ketogluconic acids. Fructose may be converted by
gluconobacter to D- threo -2,5-hexodiulose. Ascorbic acid is converted to L-xylosone.
In general, the presence of S(IV)-binding compounds cannot be avoided in fermented
beverages, but significantly higher concentrations occur when fruit has undergone
microbial spoilage through the action of molds or bacteria.
For mixtures of carbonyl compounds, the distribution of S(IV) between the
various hydroxysulfonates can be calculated, for the general case, by solving the
series of simultaneous equilibria: