A simplified HPLC method for rapid determination of folates in yeast with ultraviolet and fluorescence detection without sample purification has been developed. By use of the column Aquasil C(18), specially designed for polar analytes, and gradient elution, it was possible to separate and determine five folate derivatives: tetrahydrofolate, 5-methyltetrahydrofolate, and 5-formyltetrahydrofolate with fluorescence detection, and 10-formylfolic acid and folic acid with ultraviolet detection. The sample preparation required only a small amount of dry yeast (25-50 mg) and included an extraction of folates by heat treatment and deconjugation of folate polyglutamates to monoglutamates with the use of rat serum conjugase. Validation involved investigation of matrix effects, determination of recovery by standard addition method, repeatability, and stability tests. The dominating folate forms in commercial dry baker's yeast were found to be tetrahydrafolate and 5-methyltetrahydrofolate with a total folate content of 2890 microg/100 g (63.4 nmol/g). The simplicity of the method makes it suitable for folate screening studies of different yeast strains.

Abstract:A supercritical fluid extractionlgas chromatography method has been used to study the influence of different factors on the absorption of aroma compounds into low-density polyethylene. Factors studied included concentration of aroma substances, storage temperature, pH and interactive effects of different food components. There were no significant differences in the partition coefficients when the concentration of the flavours was varied between 0.1 and 10 mg kg-'.The storage temperature, however, affected the absorption significantly (P < 0.05), approximately twice as much was absorbed at 75°C compared with 5°C. Acidification to pH 3 with acetic acid did not significantly alter the amounts of the aromas being absorbed. Further, when occurring alone in the model solutions the aroma substances had much larger partition coefficients than when in mixtures with others, indicating an antagonistic effect of different aroma compounds on absorption. Olive oil and, thereby, the flavours dissolved in the oil, were absorbed in large amounts by the plastic. Extractions of plastic films stored in concentrated apple juice were successfully carried out. In addition to many unknown substances, nine of the 10 aromas used in the model solution were detected in the plastic stored in concentrated apple juice.

Five polymer films commonly used in food packages were stored in an aqueous solution of 10 apple aroma compounds. Substances absorbed by the polymers were determined by a supercritical fluid extraction/gas chromatography method. Polypropylene absorbed most aromas, more than 2x amounts absorbed by low density polyethylene. Polyamide and polyester absorbed very small amounts of the aromas. Esters and aldehydes were absorbed much more than alcohols. Molecular size also affected absorption, larger molecules being absorbed to a greater extent than smaller ones. For most materials the absorption equilibrium was reached within a week.

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