Biomedical Engineering Reference
In-Depth Information
a reduction of molecular weight. The effect is reversed at high concentration. Evi-
dence for a pathway that involves oxidation comes from the fact that this effect is
inhibited by conventional antioxidants. The absence of oxidative depolymerization
at high S(IV) concentration has not yet been explained satisfactorily.
These observations lead to a most intriguing question regarding the generally
accepted role of S(IV) in food as an antioxidant, whereas its behavior in model
systems can often be seen to be that of a pro-oxidant. Currently we have no evidence
that S(IV) acts as a pro-oxidant in any real food system despite the fact that S(IV)
is oxidized in food and should, therefore, provide oxidizing free radicals. There is
no scientific evidence to reconcile the anti- and pro-oxidant behavior, but such
knowledge would be fundamental to our understanding of food as a medium for
chemical reactions. The reason for the apparent contradiction is likely to lie in the
multiphase structure of food and the availability of different antioxidants in the
different phases.
FOOD APPLICATIONS
The subject of this chapter has been slanted towards the principles underlying the
interactions of sulfur dioxide with food components to provide generic understanding
of the chemistry. The reader is made aware of specific food examples to illustrate
the relevance of the chemistry throughout this chapter, but is directed to the signif-
icant reviews
1-6
for more detailed information.
It should be recognized that many “traditional foods” cannot be prepared without
this additive. They include wine, cider, perry and other fermented beverages, burger
meat with a minimum vegetable and/or cereal content of 4%, breakfast sausages,
longanzia fresca and butifarra fresca, jams, jellies, and marmalades made with
sulfited fruit, sultanas and other dehydrated fruits such as apricots, dehydrated
vegetables, barley water, and capilé groselha.
82
The production of beer with a second
fermentation in the cask (cask-conditioned or real ale) requires a relatively high level
(50 ppm) of sulfur dioxide, and is a process unique to Europe.
ALTERNATIVES TO SULFUR DIOXIDE
T
HE
N
EEDFOR
A
LTERNATIVES
This chapter describes a large number of chemical reactions involving S(IV) in foods
and it is understandable that they have caused concern about the safety of the use
of sulfur dioxide as a food additive. The toxicity of ingested S(IV) is regarded as
low on account of the very efficient sulfite oxidase detoxifying system present in
the liver of all animals.
83,84
The major reaction product from the inhibition of Maillard
browning, DSH, is metabolically inert.
85,86
The destruction of thiamin
87
is the “clas-
sical” example of an adverse effect of a food additive on the nutritional quality of
a food, but this loss of vitamin is not regarded as being of any significance in practice.
It has, however, led to the view that sulfur dioxide should not be used in foods that
are an important source of thiamin. On the other hand, the products formed when
disulfide bonds in proteins react with S(IV) (
Figure 8.6
,
reaction II) either in food
Search WWH ::
Custom Search