NEW INSIGHTS ON FACTORY INDICATORS OF FREEZE DETERIORATED CANE

摘要

CURRENTLY in the USA, there is no reliable, rapid, easy-to-use, and inexpensive method to measure cane deterioration at the factory. As a consequence, factory staff do not know quickly whether a load of cane can be processed economically or if associated processing problems are expected. For the last four years, basic studies on cane deterioration have been conducted with a final goal to develop such a method. This paper emphasises a study on the freeze-deterioration of eight commercial cane varieties. The major source of cane deterioration in the U.S., particularly under Louisiana's humid conditions, is from Leuconostoc bacteria. Up until now, the major focus of Leuconstoc cane deterioration has been the formation of dextran, but numerous other products are also formed by Leuconostoc, which are of importance in sugar manufacture, including levan and alternan polysaccharides, and mannitol. In a green, whole-stalk cane freeze-deterioration study, mannitol, produced by mannitol dehydrogenase from Leuconostoc and measured using ion chromatography, was a slightly better predictor of pressed juice viscosity (r~2 = 0.84) than both ASI-II (r~2 = 0.80) and Haze (r~2 = 0.81) dextran, because it can independently indicate all Leuconostoc polysaccharides. In comparison, ethanol (r~2 = 0.68), leucrose (r~2 = 0.71), and pH (r~2 = -0.71) were only moderately correlated with viscosity. Mannitol was also better than dextran at predicting percentage filterability of pol solutions, although substances present in the undeteriorated cane juice and sucrose interfere with this processing parameter. Strong polynomial trend or quadratic fits existed between ASI-II (enzyme method) dextran and titratable acidity (r~2 = 0.92) and pH (r~2 = -0.88). However, threshold levels exist where deterioration effects become greater than varietal effects: ～2500 ppm and ～2800 ppm/Brix dextran for titratable acidity and pH, respectively, which explains their unreliability at predicting a wide range of cane deterioration, although the measurement of a specific deterioration acid such as D or L lactic may be worthwhile. Overall, mannitol was the best predictor of cane deterioration which contributes to sucrose losses, dextran, viscosity and, to a lesser extent, filterability problems. Furthermore, mannitol does not degrade under industrial processing conditions, which gives support to the use of mannitol to indirectly measure dextran and/or cane deterioration at the factory. A reliable, rapid, easy and inexpensive enzymatic method to measure mannitol at the factory is now being investigated.