ROLE OF IRON IN CATALYSING THE CARAMELIZATION OF SUGAR AND ITS PREVENTIVE AND CURATIVE MEASURES

摘要

Formation and isolation of "iron-monosaccharide chelates" with respect to caramelization have been studied with the reappraisal of spectral and analytical evidences and their analysis is presented. The gustatory property of the isolated chelates have revealed that the chelates contained salty taste but with no metallic taste whatever and were found soluble in water so give a dark brown solution having salty, with slight caramel taste but again with no metallic taste at all. The present study revealed that the deterioration of sugar crystal does not seem to be slow traditional caramelization catalysed by alkali impurities rather it seems more likely a fast caramelization catalysed by iron introduced from sugar mills or its chelates formed with monosaccharides during processing of sugar. The comparative physico-chemical study of the isolated chelates with their analar counterparts adds our confidence of suggesting iron-sugar complexation in caramelization process. This conclusion is also found consistent with the chelating behaviour of sugars as found in their organo-metallic compounds (OMCs) which has already been confirmed by NMR and ESR techniques. Hence, removal of iron is highly essential. Addition of sodium sulphite seems to be an effective reagent for colour reduction. At pH 10 and 75°C the rate of colour formation from sucrose, glucose and fructose (3%) is reduced by about 55, 48 and 50% respectively in the presence of sodium sulphite (1%). As a curative measure coating of SO_2 gas pipe lines with TEFLON appears to be an effective means to minimize uptake of iron and consequently sugar caramelization can be reduced or controlled. Strong evidence in favour of this suggestive measure is based on our observation that minimum colour formation (368 K) was observed in 1 hr. on exposing PWS and sucrose solutions to a container made of teflon as compared to solutions in mild steel and glass containers.