Submitted to: International Sugar Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2010
Publication Date: 8/1/2010
Citation: Eggleston, G., Montes, B., Antoine, A., Stewart, D. 2010. Seasonal variations in optimized applications of intermediate stable alpha-amylase in raw sugar manufacture. International Sugar Journal. 112:472-480. Interpretive Summary: Unfortunately, the application of amylase (an enzyme) to break down long chains of unwanted, but increasing, starch in U.S. sugarcane factories is still not optimized because of misinformation about which enzyme to use, and how to add the enzyme. Final factory trials were conducted to provide more optimum conditions for amylase applications to factory staff. Amylases have been typically applied to syrup in last evaporators, but it was shown that applying working solutions of high activity amylase to the next-to-the-last evaporator provided greater starch breakdown than applying it to the last evaporator alone. Fluctuating starch concentrations across the season make standardized application of alpha-amylase impossible.
Technical Abstract: 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 and the introduction of new sugarcane varieties with higher starch content. To prevent carry-over alpha-amylase activity in molasses and raw sugar in the U.S., commercial alpha-amylases used to control starch are intermediate temperature (IT) stable and sourced from Bacillus subtilis bacteria. Alpha-Amylases have been typically applied to syrup in last evaporators where starch is solubilized and gelatinized, syrup temperatures are ~60-65 degrees C, and ~18 min retention time (Rt) is available. As IT stable alpha-amylases are effective up to 85 degrees C, they could be more effective and economical if applied to next-to-the-last evaporators where syrup temperatures are ~77 degrees C. Factory alpha-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 alpha-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 alpha-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 alpha-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 alpha-amylase. Fluctuating starch concentrations across the season make standardized application of alpha-amylase impossible.