Evidence for sulfite induced oxidative reductive depolymerisation of starch polysaccharides

The influence of low levels of sodium sulfite on the viscosity of 0.90 g/100 mL dispersions of wheat and potato starch pasted at 95 °C has been studied. It is shown that, if pasting is carried out in 0.01 g/100 mL sulfite, the viscosity of the starch following solubilisation in 0.5 M KOH is lower than a control pasted in the absence of sulfite. The starch intrinsic viscosity is also reduced after pasting in sulfite, indicating that some polysaccharide degradation has occurred. It is suggested that this is the reason for the increased release of polysaccharide from the starch granule when pasted in the presence of sulfite. For both starches the intrinsic viscosities show that there is a reduction in degradation when the sulfite level is increased or when the polar antioxidant propyl gallate is included in addition to sulfite indicating that the mechanism is oxidative reductive depolymerisation of the starch polysaccharides. It is also suggested that oxidative degradation may have an important influence on the integrity of the starch granule following pasting and may be a factor in the functional behaviour of oxidising agents in baked products. Low levels of sodium sulfite and sodium chloride both dramatically reduce the viscosity of potato starch as a result of a non-specific ionic effect.