Optimization of alpha-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 ot-amylases used by the U.S. sugar industry to control starch have intermediate temperature stability (up to 85° C with an optimum -70° C), and are produced from Bacillus subtilis. There is neither a uniform/standard method to measure the a-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° C, where a-amylases are mostly applied. Awide 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/dollar. alpha-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 a-amylase with low activity (59 KNU/ml) for an average starch hydrolysis of 6.6% as determinedwith 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 a-amylase (59 KNU/ml) at 10 ppm (undiluted) gave an average hydrolysis of 25.4% that only increasedto 28.5% at 20 ppm. Application of a B. subtilis a-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 a-amylase and starch. Application of the a-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° C) alpha-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.