Masters Theses

Date of Award

5-1989

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering

Major Professor

Luther R. Wilhelm

Committee Members

Frances A. Draughon, Zachary A. Henry

Abstract

Mold growth in stored grain has been a problem for decades. Extensive research has gone into the study of storage molds in corn, but very little work has been done with grain sorghum. This study dealt with one of the most prevalent of the storage fungi, Aspergillus parasiticus. a mold that produces a toxin that can be fatal if ingested.

This research was completed in two related segments. The first dealt with the growth and toxin production from A. parasiticus. Fifty gram samples of grain sorghum were weighed and sterile water added to bring the samples to moisture contents of 16%, 20%, and 24% (wb). These samples were then inoculated with pure A. parasiticus spores and samples of each moisture content were incubated at temperatures of 16°, 20°, 24°, and 28°C. This procedure was repeated twice with the first repetition run in triplicate.

A. parasiticus growth was subjectively recorded every two days. Samples were then extracted to isolate the aflatoxins produced. The extractions were quantitated by High Performance Liquid Chromatography (HPLC) analysis.

The second part of the research involved the evaluation of a model grain dryer. The environment within the dryer (temperature, RH of the air in and out, and the weight of the bin and grain) was recorded while drying grain sorghum initially at 20% moisture content (wb). Air flow was maintained at approximately 0.004 m3/min/L (5.00 ft3/min/bu). Samples were taken from selected locations within the drying grain every eight hours and plated to record the mold growth over a 24 hour period.

Maximum A. parasiticus growth and toxin development occurred at 28°C, 24% moisture (wb). This does not necessarily show that 28°C, 24% moisture (wb) is the optimum combination for A. parasiticus growth, but that it is the best of the combinations tested.

Mold growth in the drying bin showed no significant pattern. Growth was sporadic throughout the bin during the 24-hour period. This was due in part to the lack of homogeneity of the sorghum being dried.

Bin temperatures did show a distinct drying pattern. There was evidence that the orientation of the air flow inlet may significantly affect grain drying. Columns did not dry evenly at each level. The heated air was predicted to flow through the grain in a uniform action. Further work is needed to investigate this occurrence. There was substantial mold growth on the grain at the top of the bin after 24 hours.

Favorable conditions for mold growth were present at each level during the drying process. The amount of mold present in the bin after only 24 hours showed the need for properly drying and storing grain sorghum. If spores from toxin producing molds are present during these favorable conditions then toxins will be produced.

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