Effects of Sulfur Dioxide on Food Quality - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 269

SIV () + ( C O ) 2 ( HS ) 1 K 1 (8.13)

SIV () + ( C O ) 2 ( HS ) 2 K 2 (8.14)

M M M M

M M M M K n

SIV () + ( C O ) n ( HS ) n (8.15)

made possible by computer successive approximation methods. The most satisfac-
tory calculations of the S(IV)-binding capacity of whole beverages are still those
published for wine samples by Burroughs and Sparks, 34,39,40 who summed the con-
tributions from S(IV) bound to D- threo -2,5-hexodiulose, L-xylosone, acetaldehyde,
galacturonic acid, pyruvic acid, 2,5-diketogluconic acid, and 2-ketoglutaric acid.
Würdig and Schlotter identified 5-ketogluconic and 2-ketogalacturonic acids as
additional components but, even after including these, the authors 35 were unable to
account quantitatively for the S(IV)-binding power of the wines they had available.
These investigations all reveal that even at the lowest concentrations of free S(IV)
used in the calculations (6.4 ppm free SO 2 , 150 ppm total SO 2 ), essentially all the
acetaldehyde is present in the form of hydroxysulfonate, and is by far the most
important contributor to S(IV) binding in beverages. Both the aroma and taste of
white wine is degraded by the presence of acetaldehyde and the “anti-acetaldehyde”
property of S(IV) is considered to be one important reason why this additive is
indispensable. Any attempt to reduce the levels at which S(IV) is added in wine-
making has to be focused on a reduction in the concentrations of S(IV)-binding
compounds. However, the accumulation of some acetaldehyde is unavoidable even
when the best quality fruit is used, and fermentation in the presence of S(IV) causes
the yeasts to produce increased levels of the aldehyde.
The relative resistance of specific strains of yeast to S(IV) is important for the
selection of “desirable” strains for fermentation. Strains of Saccharomycescerevisiae
have long been regarded as particularly resistant organisms, but Saccharomycodes
ludwigii have frequently been isolated from alcoholic beverages that had been treated
with S(IV) at levels that prevent the growth of S.cerevisiae . One reason 27 for the
higher resistance of S.ludwigii is that this organism produces acetaldehyde at a
higher rate (mirrored by a reduction in free S(IV)) and the amount of S(IV) accu-
mulated in the cells is one-third that of S.cerevisiae.
In contrast to the detrimental quality characteristics of acetaldehyde in wine, it
is often used as a flavor additive in soft drink formulations to provide “impact”.
Despite the known S(IV)-binding characteristics, many beverage manufacturers are
still using acetaldehyde in S(IV)-preserved products. Figure 8.7 shows the calculated
concentration of free acetaldehyde at different total acetaldehyde and S(IV) concen-
trations, to demonstrate the very low equilibrium concentrations of the aldehyde
which might result in such a situation. Thus, the addition of acetaldehyde to flavor
a sulfited beverage is inadvisable for two reasons. First, it does not represent good
manufacturing practice to use increased levels of food additives to compensate for
losses as a result of chemical reactions between those additives. Second, the long-term