DBPapers
DOI: 10.5593/SGEM2016/B61/S25.061

CHARACTERIZATION AND BIOCONVERSION OF PENTOSAN CONTAINING BY-PRODUCTS OF WHEAT PROCESSING

B.A.Karetkin, V.I. Panfilov, N.Yu.Khromova, I.V.Shakir, A.S.Yanenko
Wednesday 7 September 2016 by Libadmin2016

References: 16th International Multidisciplinary Scientific GeoConference SGEM 2016, www.sgem.org, SGEM2016 Conference Proceedings, ISBN 978-619-7105-68-1 / ISSN 1314-2704, June 28 - July 6, 2016, Book6 Vol. 1, 463-470 pp

ABSTRACT

The pentosan-containing fraction (PCF) is a wheat processing by-product obtained in 3- phase starch decanter. It is commonly used for animal feeding. The PCF obtained in the Nivoba decanter is described in this research; its composition and potential for yeast fermentation being evaluated. The PCF was a liquid by-product containing oven-dry weight (DW) matter nearly 14 %, including 12.6 % in the dissolved form. The carbohydrates constituted 88.5 % by DW, including reducing substances of about 41.2%. The total content of pentosans (Douglas, 1981) was 16.9 % of thecarbohydrate
components, and nearly one third of them being dissolved. Glucose based of oligo-and polysaccharides prevailed, mostly the partial starch depolymerization products which did not give coloring with iodine. The strains Leucosporidium scottii and Candida utilis consuming glucose and xylose were selected based on various yeast genus growth activity (Saccharomyces, Pichia, Candida, Rhodotorula, Endomycopsis, and Leucosporidium) when comparing with their growth on synthetic media (with xylose and arabinose) and the PCF-containing media. Mineral nitrogen in the form of ammonium sulfate was enough for the needs of these microorganisms in the culture medium. Dilute sulfuric acid hydrolysis (pH 1.8-2.5, 121 °C, 30 min) did not lead to increase in consumption of carbohydrate by-products by the yeasts. The substances inhibiting the microbial growth were formed at the lower value of pH (1.2 - 1.5). Industrial enzymes for xylanase and hemicellulase hydrolysis also resulted in a slight (less than 17 %) pentosan transfer from a solid phase into the solution. As a result, it had no significant effect on the yeast yield. The yeast growth rate was about 0.17 h-1 during the batch fermentation in the bioreactor (Minifors, Infors HT) with aeration and mixing. The pentosan bioconversion took place with consumption of the reducing substances: α-amylases and glucoamylases (Duozym, Novozymes) in addition to the culture broth during the fermentation resulted in a growth rate increase up to 0.22 h-1. About 83 % of carbohydrates were consumed during the process. As a result the yeast biomass (DW) obtained contained about 53 % of the protein presented presumably with microbial and vegetable protein.

Keywords: wheat pentosans, wheat processing by-products, yeast, fermentation,
hydrolysis.