Mannitol as a Sensitive Indicator of Sugarcane Deterioration and Bacterial Contamination in Fuel Alcohol Production

摘要

Mannitol, formed mainly by Leuconostoc mesenteroides bacteria, is a very sensitive indicator of sugarcane deterioration that can predict processing problems. A rapid (4 to 7 min) enzymatic method has been developed to measure mannitol in juice pressed from consignments of sugarcane delivered to the factory. This screening tool will allow factory staff to know rapidly which consignments of cane will affect processing negatively or reject consignments that will cause unacceptable processing problems. This method can be easily performed using existing equipment in sugarcane factories, with mannitol being measured spectrophotometrically using mannitol dehydrogenase (MDH) as the enzyme catalyst. The stability of the reagents, limited cane juice preparation, linearity, accuracy, and precision are described. The method is highly specific for mannitol and is not affected by the presence of sucrose, glucose, fructose, or dextran. The current cost is only ～60 U.S. cents per analysis. Mannitol has also been proven to be an advantageous indicator of bacterial contamination - one of the main factors causing drops in fuel alcohol fermentation yields as well as yeast (Saccharomyces) flocculation and foaming problems. Compared to other indicators, mannitol is not produced by yeast cells but only by some contaminating bacteria (mostly Lactobacillus strains) during fermentation. Its presence can account for unexpected yield drops, and it can be measured easily. A strong correlation existed between mannitol formation and bacteria counts in sugarcane juice and molasses fermentations with induced mannitol producing bacterial contaminations.