Successful application of dextranase in sugar beet factories.

Dextranases are sometimes applied to hydrolyze dextran polysaccharide in sugar manufacture when bacterial (mainly Leuconostoc) deterioration of sugar beet has occurred. Unfortunately, dextranases only have a small market and low volume sales compared to many other industrial enzymes. Consequently, research and development efforts to engineer properties of dextranases to specific conditions of sugar beet processing have not occurred and are not expected soon. Less than optimum application previously existed because of confusion about where to add the dextranase in the factory and which commercial dextranase to use. The wide variation in activity of commercially available “non-concentrated” and “concentrated” dextranases in the US, Europe, and other parts of the world, and a standardized titration method to measure activities at the factory are discussed. The titration method to measure the activity of dextranases at the factory is currently an ICUMSA (International Commission for Uniform Methods in Sugar Analysis) Tentative method. Optimization by applying “concentrated” dextranase as a working solution to juice is described. The results and conclusions from a trial of dextranase addition to draft raw juice at Wissington factory in the UK are discussed with emphasis on the impact on factory throughput and other key operational parameters. The trial demonstrated a significant benefit on second carbonation filtration which resulted in increased throughput, reduction in process chemicals usage, improved operational stability, a reduction in limesalts and the amount of water discharged to the site effluent treatment plant. A concentrated dextranase gave better cost in use, because an addition rate below that recommended by the suppliers was achieved making the product significantly cheaper. Additional key words: Beta vulgaris, dextranases, optimized processing, precipitated calcium carbonate (PCC) INTRODUCTION Background Information on Dextranases The major contributor to sugar beet and sugarcane deterioration is Leuconostoc mesenteroides infections (De Bruijn, 2000, Eggleston and Monge, 2005), particularly when humid and warm environmental conditions prevail. L. mesenteroides produce dextrans ((1→6)--D-glucans) and other deterioration products including mannitol and D-lactic acid, which in moderate and severe cases can disrupt normal processing operations. Dextrans are polydisperse by nature, i.e., they exist as a wide range of molecular weights. The high viscosity associated with the high molecular weight HMW portions (> 1000 KDa) of dextran mostly affects processing. Dextrans possess a largely linear structure (Khalikova et al. 2005) comprised of ~95% glucose units linked by (1→6) glycosidic bonds, but also containing ~5% branching through (1→4), (1→3) and some (1→2) linkages. Freezes and subsequent thawing injure sugar beets and leave them susceptible to microbial infections, particularly from L. mesenteroides if warmer weather subsequently occurs.