Pauline Johanna Maria Teunissen

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™ (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™ 001 and STARGEN™ 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™ 001 and viewed using scanning electron microscopy to examine the hydrolysis action of STARGEN™ 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™ 001 and STARGEN™ 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™ 001 and STARGEN™ 002 on purified maize starch, amylopectin and amylose. Though almost twice the amylopectin was hydrolysed using STARGEN™ 002 than STARGEN™ 001 in this trial, fermentations using STARGEN™ 002 resulted in lower ethanol yields than fermentations using STARGEN™ 001. Both STARGEN™ enzyme blends were more suitable for the fermentation of high amylopectin maize starches than high amylose starches.