SULFITE AND OXIDATIVE-REDUCTIVE DEPOLYMERIZATION REACTIONS

Addition of sulphite at levels between 0.004 and 1% helps to protect t he water soluble neutral polysaccharide guar gum from thermal degradat ion. The greater the amount of sulphite incorporated the more viscous the guar is post-retorting. Starch granules, from a wide range of sour ces, swell when heated in excess water. The amount of polysaccharide r eleased from the swollen granule after pasting for 60 min at 95 degree s C is increased by the inclusion of low levels (similar to 0.01%) of sulphite. For cassava starch, a pronounced minimum in swelling volume is observed at this sulphite level. This minimum has been related to t he pro-oxidant activity of the sulphite in contrast to the antioxidant activity shown for the guar. Intrinsic viscosity data indicates that the action of the sulphite is to degrade the polysaccharides within th e starch granule and this can be reduced by scavenging oxygen from the system or by the addition of propyl gallate. It therefore appears tha t low levels of sulphite protect guar gum from degradation but can cau se degradation of the starch polysaccharides. (C) 1997 Published by El sevier Science Ltd.