Submitted to: Journal of Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2003
Publication Date: 7/21/2004
Citation: Eggleston, G., Legendre, B.L., Tew, T. 2004. Indicators of freeze-damaged sugarcane varieties which can predict processing problems. Journal of Food Chemistry. 87(1):119-133. Interpretive Summary: Freeze deterioration of sugar cane before harvesting can cause problems in factory processing leading to high sucrose and dollar losses. Present methods to measure cold tolerance or freeze deterioration in cane are not very sensitive, too time consuming or expensive, and cannot always predict processing problems. In this study, new and more sensitive indicators of cane freeze deterioration of cane were observed to predict processing problems. A compound called mannitol was identified as the most sensitive indicator of cane deterioration in the U.S. and can predict multiple factory processing problems.
Technical Abstract: Sugarcane can be very susceptible to damage by freezes, and freeze deteriorated sugarcane can cause processing problems and sometimes leads to a factory shut-down. A reliable indicator to give evidence whether a certain shipment of sugarcane can be processed economically is still needed. This study was undertaken during the 2002/2003 harvest season to measure the cold tolerance of eight commercial sugarcane varieties, and establish process indicators. Varieties included CP 70-321, CP 79-318, LHo 83-153, LCP 85-384, HoCP 85-845, HoCP 91-555, HoCP 96-540, and TucCP 77-42. Freezing temperatures occurred between Jan 18-19, and Jan 24-25, 2003. The min. field temperature recorded was -5.1oC on Jan 25. Freezing conditions prevailed for 10-14 hours during each freeze. Samples were taken one day before the first freeze on Jan 17, and subsequently again 12, 18 and 26 days post-freeze. Marked changes for most indicators of freeze deterioration for all varieties were observed, particularly 18 and 26 days post-freeze, and viscosity increased and % pol filterability decreased on freeze deterioration. Variety TucCP 77-42 had significantly (P<.05) the worst cold tolerance, even after 12 days, because it was selected in Argentina where freezes seldom occur. Strong quadratic fits existed between ASI-II dextran and titratable acidity (r2=0.916) and pH (r2=-0.883). Deterioration effects became greater than varietal effects at threshold levels of ~2500ppm and ~2800ppm/Brix dextran for titratable acidity and pH, respectively. Titratable acidity and pH may, therefore, only be useful in predicting problems caused by severe dextran concentrations. Reactions of Leuconostoc mesenteroides, including the production of dextran, levan, and alternan polysaccharides are described. Mannitol, produced by mannitol dehydrogenase from Leuconostoc, was a better predictor of viscosity (r2=0.838) than both ASI-II (r2=0.802) and haze (r2=0.814) dextran, because it can indicate all Leuconostoc polysaccharides. In comparison, ethanol (r2=0.676), leucrose (r2=0.711), and pH (r2=-0.711) were only moderately correlated with viscosity. Mannitol was also better than dextran at predicting % pol filterability. Overall, mannitol was the best predictor of sugarcane deterioration which contributes to sucrose losses, dextran, viscosity and filterability related problems. Model mannitol degradation reactions simulating industrial conditions showed no mannitol degradation occurred even after 1h at 99oC, pH 5.4 and high or low Brix, which gives further support to the use of mannitol to indirectly measure dextran and/or deterioration in the factory.