RESEARCH PAPER Structural changes of corn starch during fuel ethanol production from corn flour

Abstract

The key factor in production of fuel ethanol by simultaneous saccharification and fermentation is the efficient conversion of granular starch into ethanol. Most difficult stage in the process is the enzymatic hydrolysis of starch granules. Their supramolecular structure as well as crystallinity and presence of complexing agents are key factors for the hydrolysis process. The aim of the study was to examine structural changes in starch granules during the simultaneous processes of saccharification and fermentation of corn flour in the long-term repeated Simultaneous Saccharification and Fermentation (SSF) process with complete recycling of the stillage liquid fraction. The SSF experiments were performed using corn flour as a raw material, the STARGEN 001 preparation as a hydrolytic enzyme, and Red Star Ethanol Red (Saccharomyces cerevisiae ) fermentation yeasts. Residual starch structure after the 4 th , and the 7 th operation cycle was examined using scanning electron microscopy, X-ray diffractometry, IR spectroscopy as well as gel permeation chromatography. In spite of accumulating glycerol, organic acids and inorganic ions in the fermentation broth, the repeated batch SSF process, with stillage recycling into the fermentation phase conducted on corn flour with the use of the STARGEN 001 enzyme preparation, was found to run efficiently. The amount of unhydrolyzed residual starch was independent of the number of operation cycles. Hydrolysis of starch resulted in the formation of porous granules and a small amount of undigested granules and pyramid-shaped residuals. Crystalline and amorphous regions were evenly digested. The molecular mass distribution of residual starch after the SSF process significantly differed from that of native starch both in the region corresponding to amylopectin and to amylose, while the most distinctive changes with respect to the amylopectin/amylose ratio, i.e. in the 4th cycle the amylopectin content decreased by up to 19%.

Simultaneous saccharification and fermentation of native rye, wheat and triticale starch

“…Simultaneous hydrolysis/saccharification of native starch combined with fermentation offers many advantages. One is the possibility of working with high‐gravity mashes . Figure shows the content of total sugars and dextrin in the mashes before and after fermentation.…”

“…One is the possibility of working with high-gravity mashes. 46 Figure 4 shows the content of total sugars and dextrin in the mashes before and after fermentation. The content of total sugars in mashes with a content of 250 g d.m.…”

Effect of Pre-hydrolysis on Simultaneous Saccharification and Fermentation of Native Rye Starch

“…Finely ground raw material allows enzymes to more easily penetrate starch granules. In the case of the hydrolysis of native starch from grains, the degree of grinding is an important parameter (Szymanowska-Powalowska et al 2012). The degree of milling affects the kinetics of the enzyme and the amounts of sugars produced, because small particles provide a larger surface area (Lamsal et al 2011).…”

“…An advantage of these enzymes is their ability to perform continuous saccharification, including during fermentation. Such enzymes are highly active from the moment they are introduced into the mash and, thanks to synergistic cooperation, generate simple sugars which are fermented on a stable basis (Szymanowska-Powalowska et al 2012). This prevents the accumulation of glucose in the fermentation medium, high concentrations of which cause osmotic stress, in turn inhibiting the activity of yeast.…”

“…The most difficult stage in the efficient conversion of granular starch into ethanol is the enzymatic hydrolysis of starch granules. They key factors are the supramolecular structure, crystallinity, and presence of complexing agents (Szymanowska-Powalowska et al 2012). The effect of heat treatment below the gelatinization temperature on the susceptibility of corn, mung bean, sago, and potato starches towards granular starch hydrolysis (35°C) has been investigated by Uthumporn et al (2012).…”