Optimization of α-Amylase Application in the Sugarcane Industry

摘要

In recent years there have been warnings by some U.S. refineries that there may be a penalty for high starch concentrations in raw sugar if starch control is not improved. Most commercial α- amylases used by the U.S. sugar industry to control starch have intermediate temperature stability (up to 85 ℃ with an optimum ～70 ℃), and are produced from Bacillus subtilis. There is neither a uniform/standard method to measure the α-amylase activity in the sugar industry nor a regulatory body to issue or regulate standard activity methods and units for any commercial enzyme. A method incorporating Phadebus? blue starch tablets was modified to simulate conditions in typical last evaporators, i.e., Ph 6.4 and 65.5℃, where α-amylases are mostly applied. A wide range of activity existed for a-amylases (59.0 to 545.3 KNU/ml) that did not reflect their comparative unit costs, i.e., activity per U.S. dollar only differed 4-fold from 40.7 to 161.8 KNU/ml/$. Α-Amylase optimization trials in the last evaporator at three factories were conducted across the 2005 Louisiana processing season. Factory 1 typically applied 3.6 ppm/cane wt. Of (undiluted) B. subtilis α-amylase with low activity (59 KNU/ml) for an average starch hydrolysis of 6.6% as determined with an iodometric method, that only increased to 11.4% at a 7.2 ppm dosage. Similar disappointing results occurred at Factory 3. At Factory 2, the same α-amylase (59 KNU/ml) at 10 ppm (undiluted) gave an average hydrolysis of 25.4% that only increased to 28.5% at 20 ppm. Application of a B. subtilis α-amylase of higher activity (545.3 KNU/ml) at 2 ppm gave an average hydrolysis of 26.7%, but only increased to 29.6% at 5 ppm because of low contact between the α-amylase and starch. Application of the α-amylase as a working solution diluted 3-fold in water at the factory improved contact and starch hydrolysis from 31.9 to 42.0% at 2 and 5 ppm, respectively, and is more cost-effective than adding it undiluted. Concern about the use of engineered high temperature stability (up to 115℃) α-amylases from Bacillus licheniformis and stearothermophilus, developed for larger markets than the sugar industry, and possible carry-over activity into raw and refined sugars, molasses, and food products, are discussed.