Document Type

Thesis - Open Access

Award Date

2019

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

William Gibbons

Keywords

Dried Distillers Grains with Solubles, Enzymatic Hydrolysis, Extrusion pretreatment, Fungal fermentation

Abstract

Limited inclusion of distillers’ grains in animal feed is primarily due to low protein and high fiber content. Other elements, such as phytate phosphorus levels in DDGS are still an issue for monogastric animals such as swine, poultry, and fish. Furthermore, unabsorbed phytic acid in manure poses a high risk for environmental pollution, because bacteria can hydrolyze phytic acid into free phosphorus that can result in algal blooms and eutrophication of surface or ground water. The objective of this thesis was to improve the nutritional value of corn dried distillers’ grains with solubles (DDGS). This was done utilizing submerged fungal fermentation, enzymatic hydrolysis, and a combination of extrusion pretreatment and fungal fermentation/enzymatic hydrolysis. All treatments served as a means of degrading fiber and phytic acid while improving protein content for animal feed applications. Initially, fungal fermentations at 5, 10, and 20% solid loading rates (SLR, dry weight basis) were used to assess four fungal strains (T. reesei, N. crassa, R. oligosporus, and A. pullulans). Flask trials were incubated for 120 h at 30℃ and 150 rpm. Uninoculated control flasks were also included. Flasks were sampled at 24 h intervals, with solids recovered by centrifugation. A solubilization effect was observed at the 0 h sampling for all SLRs, as DDGS solubles fractionated into the centrate stream, while insoluble fractions such as protein and fiber were concentrated in the pellet. An increase in protein content ~5% and crude fiber ~1.5% is seen at the 5% SLR in the uninoculated control; at higher SLR the increase in protein drops to ~3% and crude fiber increases about 0.5-1%. After fermentation N. crassa (NRRL-2332) at a SLR of 20% resulted in the greatest reduction in fiber (-0.5% equal to original grain), while increasing protein (+5%) and lowering phytic acid levels (~0.3g/100g). An increase in fiber was seen in all other fungal and SLR combinations. Higher SLR resulted in better protein content for each of the fungi. Enzymatic hydrolysis under submerged conditions (10% SLR) was also tested to determine if fibrous components of the DDGS could be degraded into simple sugars. Trials were conducted in 250 ml flasks incubated for 24 h at 55℃ and 150 rpm. Four commercially available enzymes (cellulase, xylanase, phytase, pectinase) at four dosages were tested at the recommended pH levels for individual testing. Trials were also conducted to assess synergistic effects of various enzyme combinations. The greatest reduction in crude fiber for the individual enzyme was seen in the cellulase 1 and 2 mg/g dosages while the greatest reduction in NDF and ADF seen in all four dosages of pectinase. When all four enzymes were combined the greatest reduction in all fibers (crude, NDF, and ADF) was achieved. The combination of 1mg/g of xylanase, phytase, and pectinase had the most effective releases of glucose and total sugars of all individual enzymes and combinations. Overall the most effective treatments were 1m/g of cellulase, xylanase, phytase, and pectinase and 1m/g of xylanase, phytase, and pectinase. To increase the fiber hydrolysis, the use of extrusion pretreatment prior to fungal fermentation was examined. Extrusion was conducted using DDGS at a 12% moisture content, with a barrel compression ratio of 3:1 and length to diameter of 20:1 at 90-100℃ Extruded DDGS was then blended with water to a 15% SLR, autoclaved, and inoculated with T. reesei, N. crassa, R. oligosporus, or A. pullulans. Extrusion reduced crude fiber content and increased protein concentration. However, after the addition of water to create the submerged fermentation the fibers were increased. After 120h of fermentation crude fiber was significantly increased in N. crassa and A. pullulans trials. Protein was concentrated during fermentation by removal of the soluble fraction, but N. crassa was able to increase the protein ~10% from the original grain and ~5% from the un-inoculated control at 48 h. A. pullulans was also able to increase the protein significantly while T. ressei and R. oligosporus were not significantly different from the control. Lastly, the use of fungal fermentation was conducted on DDGS that was pretreated via extrusion (12% moisture, barrel temperature 90-100℃, compression ratio 3:1, barrel length to diameter 20:1) and hydrolyzed via the combination of cellulase, xylanase, pectinase, and phytase, each at dosage of 1 mg protein/dry gram of DDGS and fermented using N. crassa using sequential (4h of hydrolysis then N. crassa) or simultaneous addition. Irrespective of extrusion the use of simultaneous addition of enzyme and fungi had the greatest reduction in fiber.

Library of Congress Subject Headings

Distillers feeds.
Animal feeding.
Fermentation.
Corn as feed.

Format

application/pdf

Number of Pages

144

Publisher

South Dakota State University

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Rights Statement

In Copyright