Conversion of cane starch to fermentable sugars in cane molasses fermentation

摘要

The corn-ethanol industry's two-step enzymatic process converting corn starch to fermentable sugars, can as well be applied to the starch entering with cane the standard sugar-ethanol process. Starch is converted to low molecular weight dextrins in the juice clarifiers with high-temperature alpha-amylase, providing the well-known benefits in sugar recovery, while the dextrins are hydrolyzed with glucoamylase to fermentable sugars and converted to ethanol downstream in molasse fermentation. In a series of laboratory tests, commercial enzymes were found effective on purified cane starch as well as on the residual starch in industrial vinasse samples, two nearly sugar-free substrates where HPLC analysis can detect the small increments in glucose and maltose from the enzymatic action on starch. In several well-controlled fermentations of molasses from various Tucuman sugar mills, with and without glucoamylase, the ethanol yield increased by 0,7% with respect to the standard enzyme-free fermentation. This agrees well with the potential gain estimated from the usual starch levels in cane juice. The 6 % ethanol gain reported recently in fermentations of Egyptian cane molasses was not confirmed. However, even with the smaller gain obtained in this work, the cost of the glucoamylase is likely much less than the value of the additional ethanol produced.