Understanding the Effect of Non-starch Grain Components on the Amylolysis of Starch in Whole Grains

• Author / Creator

  Kandil, Amin AA

• Bioethanol industry is fast growing as it is a clean substitute of fossil-fuel. Starch is a clean, cheap & non-toxic source for bioethanol production. Efficient conversion of starch to fermentable sugars is important. The objective of this research was to investigate the effect of non-starch grain components on the amylolysis of starches isolated from triticale, wheat, corn and barley grains. Dry-milling and non-starch components of flours may impact the enzymatic hydrolysis of starch to glucose. The particle size distributions of ground flours from whole grain triticale, barley, wheat and corn were evaluated and the effects of pre-washing with water, hexane, 100% ethanol or 50% ethanol on flour composition and the amylolysis of starch were studied. Grinding grain to pass through a 0.5 mm sieve effectively released starch granules from endosperm cells. Pre-washing with water or 50% ethanol decreased the protein, phytic acid and total phenolics contents of flours and, except for corn flour, increased starch content. Pre-washing with water reduced the β-glucan content of barley flour by 98%. Pre-washing with hexane or 100% ethanol removed about 80 to 97% of the lipid from the flours. Each of the pre-washings was associated with a significant change, positive or negative, in the extent of α-amylolysis for one or more of the flours. The degree of α-amylolysis in the unwashed flours ranged from 22.4-26.1%, and from 21.6-28.1% in pre-washed flours. Pre-washing of flours increased the degree of hydrolysis achieved with a sequential α-amylase/amyloglucosidase treatment, with values ranging from 61.4-72.8% in pre-washed flours compared to 56.2-57.8% in unwashed flours. The highest degrees of hydrolysis were achieved with 50% ethanol pre-washing at 72.4 and 72.8% for triticale and barley flours, respectively. The degree of α-amylase/amyloglucosidase hydrolysis obtained for isolated starches ranged from 83.7-93.0%. This study clearly demonstrated that the partial removal of non-starch components from whole grain flours by solvent pre-washing enhanced the degree of amylolysis of starch. The presence of phenolics in cereal grain is thought to influence starch amylolysis during liquefaction and saccharification of whole grain flours. To understand amylolysis systems and inhibition mechanisms, the composition and concentration of phenolic acids in whole grain flours of triticale, wheat, barley and corn were analyzed by HPLC. The total phenolic acid contents, representing the sum of 11 phenolic acids in each of the four grains, were 1171, 1732, 1599 and 2331 µg/g, respectively, with more than 76% found in the bound form. Ferulic, coumaric and protocatechuic acids were the major phenolic acids in triticale and wheat. Gallic acid also was rich in triticale. Ferulic, coumaric, hydroxybenzoic, gallic acids and catechinhydrate were predominant in barley. In corn, ferulic, coumaric, gallic, catechinhydrate, naringin, and syringic acids were abundant. Based on these profiles, pure phenolic acids were added individually and collectively to isolated starches at amounts either equivalent to or three times those in the whole grains. The degree of starch hydrolysis with α-amylase and amyloglucosidase decreased up to 8% when individual phenolic acids were added. The decreases were more pronounced when phenolic acids were added collectively (4-5% with α-amylase and 9-13% with sequential α-amylase and amyloglucosidase). Study of a phenolic acid-starch-enzyme model system indicated that a phenolic acid-enzyme interaction was the dominant contributor to the interference, but a phenolic acid-starch/dextrin interaction also played a significant role. Heating augmented the interaction between phenolic acids and the enzymes and starch/dextrin. Phenolic acids thus can contribute to the resistance of starch to enzymatic hydrolysis and/or the loss of enzyme activity during starch amylolysis. The effect of phenolic acids on starch amylolysis in their bound or “native” form as exists in the bran and also in the free form. Three different fiber concentrates (FC) were used in this study; one contained bound phenolic acids (FC1), one contained free phenolic acids (FC2), and the third had no phenolic acids (FC3). The degree of starch amylolysis of triticale, wheat, corn and barley flours were most significantly decreased (p< 0.05) by adding FC2, and next by FC1, and least by FC3.(19, 9.1 and 4.8%, respectively, for liquefaction with alpha-amylase and (14.25, 4.6 and 2.7%, respectively for liquefaction and saccharification with amyloglucosidase).

• Subjects / Keywords

  • Pre-washing
  • Phenolic acids
  • Amylolysis
  • Starch hydrolysis
  • Bioethanol
  • Non-starch components

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3V40K91J

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.