Date of Award

12-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Agricultural and Biological Engineering

First Advisor

Richard L. Stroshine

Second Advisor

Klein E. Ileleji

Committee Chair

Richard L. Stroshine

Committee Co-Chair

Klein E. Ileleji

Committee Member 1

Shawn S. Donkin

Committee Member 2

Kevin M. Keener

Committee Member 3

Charles P. Woloshuk

Abstract

The overall goal of this project was to reduce the aflatoxin level in the final coproduct of ethanol bioprocessing--DDGS. This was pursued by examining the effects of reduction of aflatoxin in the incoming corn prior to bioprocessing, the degradation of aflatoxin in the intermediate products, namely DWG and CDS, during processing, and aflatoxin degradation in the DDGS. Segregation techniques (size screening and density sorting) and detoxification methods (conventional and microwave heating, food additives, and high voltage atmospheric cold plasma) were evaluated for their effectiveness in aflatoxin reduction.

Effectiveness of physical segregation of aflatoxin contaminated corn was investigated by size screening and density sorting in a 737 kg corn lot with an aflatoxin level of 185 ppb. There are statistically significant differences in major and minor diameters, the sphericities and the densities between moldy and healthy corn kernels. The moldy corn kernels had a smaller major diameter, greater sphericity and a lower density. Results indicated that removal of fine material from the corn lot through size screening could significantly reduce aflatoxin in the remaining lot. Further removal of small size kernels through cleaning with a screen cleaner and removal of lower density kernels with a gravity table gave an additional reduction of aflatoxin in the remaining corn lot.

Reductions of aflatoxin achieved by conventional heating (using a convection oven and water bath) and microwave heating to degrade the aflatoxin were also investigated. The presence of water is critical to aflatoxin degradation during heating. Aflatoxin is very stable during dry heating and a temperature of 150 ºC is required to initiate decomposition of aflatoxin. HPLC-MS studies revealed that aflatoxin B1 was converted into its enantiomer by dry heating. During wet heating for 1 h at 80°C, 73% of the AFB1 was degraded. Degradation of AFB1 by wet heating involves hydrolysis of the furofuran moiety and the lactone ring along with further decarboxylation. Microwave heating produced the same degradation products as conventional heating, indicating that degradation during microwave heating is purely due to its thermal effects.

Degradation of aflatoxin by food additives was also investigated. Four selected food additives, i.e., sodium bisulfite, sodium hypochlorite, citric acid, and ammonium persulfate, were able to effectively (>86%) degrade aflatoxin with no substrate by heating at 90 ºC for 1 h with 1% (by weight) food additive solutions. A protective effect of the substrate was found for aflatoxin degradation in DWG and CDS. Citric acid is the most promising additive for degrading aflatoxin since it has been classified as GRAS (generally recognized as safe) by FDA. Degradation of aflatoxin B1 by citric acid was through acid-catalyzed hydrolysis which converts the AFB1 to AFB2 and AFB 1-Citric (C23 H19 O13). Aflatoxin reduction was enhanced by adding more citric acid and prolonging the heating time.

Performance of the HVACP system and generation of reactive species were characterized using optical emission spectroscopy and optical absorption spectroscopy. During the 120 s HVACP treatment, ozone concentrations generated by HVACP follows a logarithmic function for both the gas MA and air (R2 adj > 0.98). Ozone generation rate and final ozone was higher when the MA gas was used instead of air, and when the relative humidity was low (5%). Aflatoxin in corn could be degraded by HVACP treatment within minutes. Three kinetic models (a first-order, a Weibull, and a logistic model) were fitted to the aflatoxin degradation data. The logistic model was found to be the best to describe the degradation kinetics of aflatoxin by HVACP with a high coefficient of determination (R2 ≥ 0.99). Degradation of aflatoxin by HVACP was influenced by the type of materials treated. It was more readily degraded in DWG and DDG than in DDGS and CDS. A Relative Importance Analysis indicated that sample amount, treatment time, and grain depth were critical parameters that determine percent reduction of aflatoxin in DDGS by HVACP Treatment. The mechanism whereby AFB1 is degraded during HVACP treatment involved hydrogenation, hydration, and oxidation of the furan ring. The hydrogen radical, hydroxyl radical, hydroperoxyl radical and ozone were proposed as the major reactive agents for AFB1 degradation generated by HVACP treatment. Based on the literature, the degradation produced changes in the furofuran and lactone rings, and cyclopantenone and methoxyl structures. These should pose less of a risk to biological activity than AFB 1 according to their structure-bioactivity relationship. (Abstract shortened by ProQuest.)

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