29B-29 |
Oxidation of long-chained aldehydes in grain sorghum wax during storage |
K. T. HWANG, Department of Food Science & Human Nutrition, Chonbuk National University, Jeonju, Jeonbuk, 561-756, South Korea, C. L. Weller, S. L. Cuppett, Dept. of Food Science & Technology, Univ. of Nebraska, Lincoln, 352 Food Industry Complex, Lincoln, NE 68583-0919, and M. A. Hanna, Industrial Agricultural Products Center, Univ. of Nebraska, Lincoln, 211 L.W. Chase Hall, Lincoln, NE 68583-0730. About 0.2% (w/w) of wax can be recovered from grain sorghum by extraction with hexane. The wax extracted from grain sorghum is mainly composed of long-chained aldehydes, alcohols and acids with aldehydes comprising about half of the wax. The aldehydes are expected to be easily oxidized to form acids when exposed to the air. The objective of the study was to determine changes in the major component and the melting point of the aldehyde fraction of grain sorghum wax during storage. Wax was extracted from grain sorghum whole kernels using hot hexane. The aldehyde fraction was separated from other fractions in the wax using silica column chromatography with hexane and chloroform. Recovered, solid aldehyde fraction was redissolved in hexane or chloroform, followed by solvent removal using a nitrogen stream. Residual aldehyde fraction was stored at room temperature under the sunlight. Composition of the major components in the stored sample was determined using HPLC equipped with a silica column and ELSD. Melting point of the aldehyde fraction was measured using a differential scanning calorimeter. Acid content in aldehyde fraction, initially at 5-7%, increased to 42-51% during 135 day storage at room temperature under sunlight. Melting point, initially at 73-74 degrees C, increased to 80-81 degrees C on day 135. Sorghum wax, containing all fractions and initially composed of 55% aldehydes, 37% alcohols and 7% acids, had a little increase in acid level to 8-12% during storage over 5 months under various conditions. The melting point of the wax (83-84 degrees C) remained essentially the same over the 5 month storage. While long-chained aldehydes fractionated from grain sorghum wax were apparently oxidized to acids during storage, the aldehydes present in the whole wax little oxidized. The stability of the aldehydes in grain sorghum wax implies changes in properties over time cannot be attributed to oxidation of the aldehyde fraction.
Session 29B, Food Chemistry: Lipids, antioxidants and emulsifiers
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