Scanning electron microscopy and fermentation studies on selected known maize starch mutants using STARGEN™ enzyme blends

The conversion of maize (corn) kernels to bio-ethanol is an energy-intensive process involving many stages. One step typically required is the liquefaction of the ground kernel to enable enzyme hydrolysation of the starch to glucose. The enzyme blends STARGEN TM (Genencor) are capable of hydrolysing starch granules without liquefaction, reducing energy inputs and increasing efficiency. Studies were conducted on maize starch mutants amylose extender 1 (ae1), dull 1 (du1) and waxy 1 (wx1) in the inbred line Oh43 to determine whether different maize starches affected hydrolysation rates by STARGEN TM 001 and STARGEN TM 002. All mutants contained similar proportions of starch in the kernel but varied in the amylose to amylopectin ratio. Ground maize kernels were incubated with STARGEN TM 001 and viewed using scanning electron microscopy to examine the hydrolysis action of STARGEN TM 001 on the starch granules. The ae1 mutant exhibited noticeably less enzymic hydrolysis action, on the granules visualised, than wx1 and background line Oh43. Kernels were batch-fermented with STARGEN TM 001 and STARGEN TM 002. The ae1 mutant exhibited a 50% lower ethanol yield compared to the wx1 mutant and background line. A final study compared hydrolysation rates of STARGEN TM 001 and STARGEN TM 002 on purified maize starch, amylopectin and amylose. Though almost twice the amylopectin was hydrolysed using STARGEN TM 002 than STARGEN TM 001 in this trial, fermentations using STARGEN TM 002 resulted in lower ethanol yields than fermentations using STARGEN TM 001. Both STARGEN TM enzyme blends were more suitable for the fermentation of high amylopectin maize starches than high amylose starches.