Dextran products of various molecular weight result from infections of Leuconostoc sp. Also, a needle like elongation of the c axis of the crystal may be caused by highly 1-6 linked dextran. However, 1-4 and 1-3 linkages also yield refractory and slowboiling syrups, but show little c axis elongation (Cossairt, 1982). It is also reported that smaller molecular weight dextrans are especially involved in the effect of c axis elongation (Singleton, 2002)

From the processing point of view the development of re-entrant angles with their effects is becoming worse as aggregates become more complex. These re-entrant angles are traps for mother liquor and zones, which are extraordinarily difficult to wash for the removal of impurities (non-sugars). The trapped mother liquor may even be present as inclusions between the individual conglomerated crystals (Houghton, 1998).

The effect that dextran has on sugar crystal shape, to elongate the crystal or cause needle grain, also increases the loss to molasses by blinding centrifugal screens with elongated crystals (Imrie and Tilbury, 1972)

2.7The Economic gain

In a sugar factory, the crystallization is an important step, which determines the yield of the sugar from sugar beet and cane. About 85% of the present sugar (sucrose) in sugar beet can be crystallized as sugar product (Figure 14). The sugar losses are almost 3% during the extraction and clarification processes and around 12% to molasses (Ekelhof, 1997).

The existence of quality points for dextran in raw sugar contracts has provided a standard for a penalty by refiners. The penalty is calculated from a sliding scale based upon the sugar dextran concentration.

Molasses

Figure 14: Partitions of sugar loss during different process stages of sugar production (Ekelhof, 1997)

Studies in Australia have shown a sugar loss to molasses of 1.2 to 1.4 purity points, which can be expected for every 1,000 mg/kg DS of dextran in molasses. This is equivalent to about 250 mg/kg DS in mixed juice (Miller and Wright, 1977).

It is estimated that for every 300 mg/kg DS dextran in syrup there is a 1% increase in molasses purity (the percentage ratio of sucrose in total solids in a sugar solution) (Atkins and McCowage, 1984; Clarke et al., 1997; Godshall et al., 1994; Guglielmone et al., 2000).

The presence of dextran above 250 mg/kg DS on solids in raw sugar brings forth penalties from the sugar refiner (Chung, 2000; Day, 1992). Effects of dextran in juice are shown in Table 5.

The economic losses caused by dextran are continuous throughout the process, since its early content in the juices falsely increases the amount of sugar calculated for them and alters the production indicators of the factory. This is due to the dextrorotatory characteristic of dextrans that polarize approximately three times more than sucrose producing a high false polarization value (Jimenez, 2005).

The evaluation of dextran levels in raw sugars with the respective sucrose losses incurred to produce these dextran levels and the amounts of fructose and acids (about 30% yield) formed is shown in Table 6

Table 6: Dextran levels and sucrose loss in raw sugars (Bose and Singh, 1981)

These amounts of sucrose loss represent only those lost directly due to dextran formation. Three to five times of these levels may be lost later in processing because of the other organic material formed conjointly with dextran (Bose and Singh, 1981).

Dextran content in sugar is a major concern for end users such as candy manufacturers. Contamination of the sugar with dextran, above a certain ppm level, will affect hard candy processing. The impact is measured in changes in candy thickness/weight and is related to dextran content in sugar (Haynes, 2004; Jimenez, 2005).