Differences in carbon dioxide evolution from samples of shelled corn subjected to various storage treatments

Author

Cininta ALP Pertiwi, Purdue University

Date of Award

Summer 2014

Degree Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Agricultural and Biological Engineering

First Advisor

Richard L. Stroshine

Committee Chair

Richard L. Stroshine

Committee Member 1

Klein E. Ileleji

Committee Member 2

Jeffrey J. Volenec

Abstract

Shelled corn was collected from two sources - commercial grain elevators and corn harvested from Purdue University farms and then frozen until tested. Using a carbon dioxide (CO₂) test kit manufactured by Woods End Laboratories, CO₂ evolution measurements were conducted on shelled corn from both sources, after the samples were re-wetted to approximately 21% moisture content, placed in a 473 ml glass jar, and incubated at room temperature for 72 hours. The CO₂ test kit uses a gel that changes color in response to a change in the level of CO₂ in the surrounding air. The color is quantified by means of a color number that can be converted to the level of CO₂ in the air using an exponential equation. A plot of color number versus time was used as the primary indicator of the CO₂ evolution of the sample being tested. CO₂ evolution is hypothesized to be an indicator for fungal susceptibility. Fungal susceptibility is a measure of the likelihood of spoilage due to fungal growth during subsequent storage or shipment when conditions are favorable for fungal growth. Shelled corn is routinely stored for 2 to 12 months before it is utilized. During this period, changes in environmental conditions can trigger fungal growth, causing spoilage of the grain. The overall objective of this study was to determine the feasibility of utilizing the CO₂ test kit in management of shelled corn during storage, which would be possible if it is assumed that CO₂ evolution during the tests is related to potential for spoilage when conditions favorable for mold growth develop. The specific objectives were to examine whether the test kit can detect 1) differences in CO ₂ evolution among corn shipments originating from commercial elevators, 2) changes in CO₂ evolution with time of storage using samples of shelled corn obtained from commercial grain elevators and stored in the laboratory for 8 to 14 months and 3) effects of moisture content and storage time on changes in CO₂ evolution from corn that was harvested and shelled in a known manner and then frozen at -20°C until tested. Samples from commercial storage facilities were used in experiments associated with the first and second objectives while corn harvested from Purdue University farms was used in experiments associated with the third objective. The results suggested that the test kit was able to identify differences in CO₂ evolution among the corn samples obtained from the commercial storage facilities. An attribute designated Slope73_75 was obtained from the color number measurements using the test kit. It was identified as the best indicator of differences in CO₂evolution among the corn samples. A 24 hour "in situ" test was conducted by the grain inspection service that collected the commercial samples. In this test, the CO₂ kit was used to test the sample after 24 hours of incubation, when the sample was tested at its original moisture content. There was a small correlation between the "in-situ" reading and the 75^th hour reading (r² = 0.270) and between the "in-situ" reading and Slope 73_75 (r² = 0.294). The test kit was also able to detect changes in CO₂ evolution caused by subsequent storage of samples from the same commercial shipments when they were stored for 8 to 14 months at room temperature. For six of the eight samples tested, the CO₂ evolution rate detected by the test kit increased between the original measurement and both second and third measurements made after storage for 8 to 14 months. There was little or no change in the two remaining samples. There were small correlations between Slope73_75 and grade number, total damage kernels (DKT), and percent BCFM (r² values between 0.199 and 0.296). Differences in moisture content of the corn at the time the sample was collected, differences in the U.S. grade factors, and differences in electrolyte leakage could not be individually identified as the reason there was no apparent change in the in CO₂ evolution of the two samples. The test kit was also able to distinguish differences in CO₂ evolution among the corn samples that were harvested, frozen until tested, and then removed from storage and placed in plastic buckets at room temperature. The observed differences were associated with moisture content at which the samples were stored in the laboratory and length of time in storage at room temperature. Differences in physical damage to the kernels were also associated with differences in CO₂ evolution. Unexpected differences in CO₂evolution among samples could be explained by a high level of physical damage in one of the samples tested. Germination tests were also conducted. The results also revealed that seed respiration may make a significant contribution to CO₂ production measured by the CO₂ test kit and that it needs to be taken into account when test kit results are interpreted.

Recommended Citation

Pertiwi, Cininta ALP, "Differences in carbon dioxide evolution from samples of shelled corn subjected to various storage treatments" (2014). Open Access Theses. 667.
https://docs.lib.purdue.edu/open_access_theses/667