Relative and Quantitative Changes in Total Vitamin E and Isomer Content of Barley During Conventional and Airtight Storage with Special Reference to Annual Variations

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Abstract
The total vitamin E content and the distribution of tocopherol and tocotrienol isomers were studied in warm-air-dried barley at 13% moisture during storage in conventional silo and in damp barley at 23 and 28% moisture during airtight storage in experimental silos, with or without an expansion sack and external CO2 supply. The tocopherols and tocotrienols in the grain were analyzed using high pressure liquid chromatography with fluorescence detection. The occurrence of large annual variations in the total vitamin E content in the barley was established by comparing the harvest values of a poor year, 1980, to those of good harvest years, 1981 and 1982. These annual differences indicate the need for yearly analyses of the vitamin E in cereal grains immediately after harvest. The total vitamin E content in warm-air-dried barley showed a monthly loss of ca. [circa] 1% during storage in the conventional silo. The isomer distribution was stable for the entire observation period of 11 mo. Total vitamin E content of barley at 23% moisture decreased from 92 mg/kg d.m. [dry matter] to about 20 mg/kg d.m. during 11 mo. storage in an airtight silo without expansion sack or external CO2 supply. Fitting the experimental silos with a pressure equalizing sack or providing external CO2-supply had a preservative effect. Generally, the barley at 28% moisture had the greatest loss in vitamin E during airtight storage. The total vitamin E content decreased from about 80 to 10-15 mg/kg d.m. The presence of an expansion sack in the bin exerted a preservative effect on the vitamin E content of barley even at this moisture content. In damp barley at both 23 and 28% moisture, the relative content of tocopherol isomers generally increased during airtight storage at the expenses of the tocotrienols, which at the same time showed a tendency to decrease. This shifting phenomenon was more prominent in the barley at 28% moisture. The absolute amounts of .alpha.-tocotrienol and .alpha.-tocopherol tended to increase during the first 2-3 mo. of airtight storage, while those of .beta.-tocotrienol and .gamma.-tocopherol decreased. This was due to the methylation of the other isomers, to produce .alpha.-isomers, while the change in the relative distribution of isomers may have reflected the saturation of the tocotrienol side chains.