Eggleston G.,U.S. Department of Agriculture |
Montes B.,Alma Plantation LLC |
Antoine A.,U.S. Department of Agriculture |
Stewart D.,Alma Plantation LLC
International Sugar Journal | Year: 2010
In recent years, starch being delivered to and processed in U.S. factories has risen markedly because of the increased production of green (unburnt) and combine-harvested (billeted) sugarcane as well as the introduction of new sugarcane varieties with higher starch content. This has led to 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. To prevent carryover α-amylase activity in molasses and raw sugar in the U.S., commercial α-amylases used to control starch are intermediate temperature (IT) stable and sourced from Bacillus subtilis bacteria. α-Amylases have been typically applied to syrup in last evaporators where starch is solubilized and gelatinized, syrup temperatures are ∼60-65°C, and ∼18 min retention time (Rt) is available. As IT stable α-amylases are effective up to 85°C, they could be more effective and economical if applied to next-to-the-last evaporators where syrup temperatures are ∼77°C. Factory α-amylase trials were conducted across the 2007 Louisiana processing season (Oct-Dec). Application of a working solution (diluted 3-fold in water at the factory) of IT stable α-amylase of high activity per unit cost (118.3 KNU/ml/$) to the next-to-the-last evaporator provided significantly (P<.05) greater starch hydrolysis (up to 78.0% at a 5 ppm/ cane wt dose) than applying it to the last evaporator alone (only up to 59.8% at a 5 ppm/cane wt dose). Reasons for the improved starch hydrolysis in the next-to-the-last than the last evaporator are multi-fold: (i) the lower Brix levels in the next-to-the last evaporator improve α-amylase action, (ii) more water is available as a reactant for the hydrolysis reaction, and (iii) there is more time for the hydrolysis reaction to occur. Starch hydrolysis, generally, increased polynomially with increasing initial concentrations of starch in syrups. Seasonal variations in starch concentrations affected the application of α-amylase to next-to-the-last evaporator more than to the last evaporator alone. Significantly (P<.05) less starch was hydrolyzed with lower precision when starch concentrations were <1000 ppm/Brix in late season (Dec), because of lower contact between the starch and α-amylase. Fluctuating starch concentrations across the season make standardized application of α-amylase impossible. Final recommendations are provided.