SORPTION AND REACTION OF SULFUR DIOXIDE ON YELLOW DENT CORN
Abstract
Sulfur dioxide can be applied as a gas to high moisture corn during low-temperature drying to control microbial growth. The efficacy of the treatment depends upon the level of SO(,2) obtained and maintained during the drying of the corn. Prediction of these levels through kinetic modeling will aid in the development of appropriate treatment procedures. The factors affecting the rate of SO(,2) loss in yellow dent corn were determined over the temperature range -16(DEGREES)C to 32(DEGREES)C, moisture contents 15% to 38%, and initial SO(,2) levels from 100 ppm to 4900 ppm. The loss followed first order kinetics with rate constants in the range 2 x 10('-9) s('-1) to 2 x 10('-6) s('-1). The Arrhenius activation energy on whole kernels was determined at 54.9 kJ-mol('-1), while on ground corn it was 17.0 kJ-mol('-1). The rate constant doubled with doubling of the moisture content and a strong dependence upon the initial SO(,2) level was observed. This dependence is apparently due to the slower rate of reaction of bisulfite ions and it is suggested that the magnitude of the dependence is controlled by the Ca/(Mg + Na) ratio in the corn. Differences were observed between the SO(,2) levels determined by the water-extractable procedure of Eckhoff and Okos (1983) and the distillation procedure described by Pearson (1977). The magnitude of the difference was a linear function of initial SO(,2) level. After 2 months of storage at 22(DEGREES)C, 63% of the total sulfur could only be accounted for as a volatile sulfur compound that does not react with iodine or lead acetate paper. During the same period, 75% of the non-water soluble protein was solubilized. The mode of entry of sulfur dioxide into the kernel was determined to be through the tip cap. Soprtion was modeled using the rate expression of Ritchie (1977) and the rate constant was found to be independent of SO(,2) concentration and moisture content over the range 20% to 38% M.C. It followed an Arrhenius type temperature dependence with an activation energy of 29.9 kJ-mol('-1). Gas diffusion through the interstitial moisture is suggested as the mode of SO(,2) transport throughout the kernel.
Degree
Ph.D.
Subject Area
Agricultural engineering
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