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The Se concentration of foods can be increased by supplementing fertilizers with soluble Se compounds. In Finland the availability of soil Se for plants is poor owing to the relatively low Se concentration, low pH and high iron content of the soil. Since 1984 multimineral fertilizers have been supplemented with Se (16 mg kg-1 to fertilizers for grain production and 6 mg kg-1 to those for fodder production) in the form of sodium selenate. Within two years a three-fold increase of mean Se intake was observed. The supplementation affected the Se content of all major food groups with the exception of fish. The concomitant human serum Se concentration increased by 70%. In 1990 the amount of Se that was supplemented was reduced to 6 mg kg-1 for all fertilizers. This reduced the mean Se intake by 30% and the serum Se concentration decreased by 25% from the highest levels observed in 1989. Plants take up part of the supplemented selenate and transform it into organic Se compounds, mainly selenomethionine. This affects human nutrition by increasing the Se content of foods of both animal and vegetable origin. According to data obtained in Finland, supplementation of fertilizers with Se is a safe and effective means of increasing the Se intake of both animals and humans that is feasible in countries with relatively uniform geochemical conditions. This kind of intervention requires careful monitoring of the effects on both animal and human nutrition and the environment.

A reversed-phase high-performance liquid chromatographic method with fluorescence and ultraviolet detection was used to evaluate the different steps in folate analysis to detect and quantify the most abundant folate forms naturally present in foods. Rapid heat extraction by microwave heating and an enzymatic deconjugation with hog kidney conjugase and chicken pancreas is presented. The extracts were purified with strong anion-exchange cartridges before injection. The combined use of ascorbic acid and mercaptoethanol in the extraction step noticeably improved the stability of tetrahydrofolate, making it also possible to analyze some of the most labile folate vitamers. Tetrahydrofolate was also shown to be easily degraded during the deconjugation step. The compounds 5-methyltetrahydrofolate and, to a lesser extent, 5-formyltetrahydrofolates were also found as important vitamers in foods. In addition, folic acid and 10-formylfolic acid could be determined with the described method. Keywords: Folates; folic acid; food; HPLC

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