Effect of dextran and enzymatically decomposed dextran on calcium carbonate precipitation

摘要

The effect of dextran's molecular mass distribution (T40, T500, T2000, and enzymatically decomposed T2000) on the size and shape of calcium carbonate particles precipitated during carbonation, a step in the sugar manufacturing process, was investigated. Image analysis combined with size exclusion chromatography was used to distinguish harmful and harmless dextran sizes aiming at targeted mitigation of dextran-related effects by dextranase. The data indicate that dextran with molecular masses above 10 kDa promotes agglomeration, indicated by an increase in particle projection area. This effect was especially found for broadly distributed intermediate but rather low molecular mass dextran (10-85 kDa). Based on particle shape data, the agglomeration of calcium carbonate crystals in the absence and in the presence of low molecular mass dextran (85 kDa) appears to be oriented and similar to each other. In contrast, the data suggest that high molecular mass dextran (85 kDa) promotes nonoriented agglomeration and an increase in surface roughness. Once the dextran was significantly decomposed by enzyme action (10 or 50 mg/kg juice) to smaller molecules in the size range below 10 kDa, no dextran-related effects on particle size and shape were found anymore. Practical applications The presence of dextran is known to cause several adverse effects during sugar manufacture. Among them, dextran can affect the size and shape distribution of calcium carbonate particles precipitated during carbonation as a part of the sugar beet raw juice purification. As a result, the purification as well as the filtration process can be affected. These dextran-related effects are usually mitigated by enzymatic decomposition, a gradual reduction in molecular mass. For a targeted enzyme application, the decomposition products need to be identified and the corresponding effects due to varying molecular mass fractions on the precipitation of calcium carbonate need to be analyzed. Only then, a sufficient decomposition to harmless molecule sizes can be ensured. Thus, the data gathered give a clear guidance for dextranase treatment in sugar manufacture.