Bound sulphite

CR Warner, DH Daniels, MC Fitzgerald, FL Joe Jr, GW Diachenko. Determination of free and reversibly bound sulphite in foods by reverse-phase, ion pairing HPLC. Food Addit Contam 7 515-581, 1990. 

Other reactions involving this aldehyde include the following (1) combination with sulphite ion, which substantially increases the proportion of bound sulphite in wine (2) formation of addition compounds with some polyphenols such as tannins and procyanidins, where it acts as a bridging molecule (Haslam and Lilley 1998) and (3) chemical oxidation to acetic acid, which only occurs to a small extent and has little influence on wine composition and quality. 

Sulphites exist in the free and bound form in foods (Wedzicha, 1984). The free sulphite consists of sulphite ion, bisulphite ion and sulphur dioxide. Reversibly bound sulphite can dissociate under the right conditions to form free sulphite but irreversibly bound sulphite cannot dissociate. 

L Pizzoferrato, G Di Lullo, E Quattrucci. Determination of free, bound and total sulphites in foods by indirect photometry-HPLC. Food Chem 63 275 -279, 1998. 

The microbiocidal effect increases as the pH falls below 4.0, and because of this S02 is ideally suited for most soft drink formulations. However, its preserving action is impaired by a tendency to react with many of the fruit components of soft drinks to form organic sulphites, in which state the S02 is said to be bound . Although the preservative properties are due mainly to free S02, it is necessary to analyse for total S02 (i.e. free plus bound) as legislation for safe levels refers only to maximum total concentrations. 

Eu(N03)3 has been shown to form essentially 1 1 adducts with L-azetidine-2-carboxylic acid (480) and Eu(fod)3 forms similar adducts with dialkylnitrosamines. (487) 1 1 Stoichiometry between Eu(fod)3 and various cyclic 6-membered sulphites has been assumed. (488) Both 1 1 and 1 2 adducts have been reported for Eu(fod)3 bound to cyclohexanones and cyclohexanols, (489) n-hexylamine, (490) hexamethylphosphoramide, (491,492) and methyl dimethylcarbamate. (493)... 

Sttrbo, B., 1957, Sulphite and complex-bound cyanide as sulphur acceptors for rhodanese, ActaChem, Scand,11 628. 

The mechanisms involved are not fully worked out. It appears that all the intermediates remain bound to protein carriers. Evidence has been obtained that the initial reduction step sulphate reductase) involves two reactions, a low molecular weight hydrogen transporting protein, and reduced FAD as the electron donor. The details of the further reduction steps are even more obscure. It has been suggested that the whole 6-electron oxidoreduction is catalysed by a single eniyme [sulphite reductase) and that reduced NADP is the electron donor. 

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