Adequacy of extraction techniques for determination of folate in foods and other biological materials
1990
Gregory, J.F. III. | Engelhardt, R. | Bhandari, S.D. | Sartain, D.B. | Gustafson, S.K.
Accuracy in the determination of folate is dependent, in part, on the completeness of extraction of folates from the sample matrix and their stability during extraction. In this study, the merits of extraction procedures employing acetate buffer (50 mM ascorbate, pH 4.9) (Gregory el al., 1984. J. Nutr. 114:341-353), phosphate (50 mM ascorbate, pH 7.0). or mixed Hepes/Ches buffers (101 mM ascorbate and 200 mM 2-mercaptoethanol, pH 7.85) (Wilson and Horne, 1984, Anal. Biochem. 142:529-535) were evaluated. In a preliminary experiment, the pH of the buffer (pH 4.9 vs 7.0) did not consistently affect the recovery of radiolabeled mono- and polyglutamyl folates added to various food homogenates. However, radiolabeled folates from the livers of rats previously dosed with [3H]folate were more effectively extracted at pH 7.0 and 7.85 than at 4.9. Microbiological assay of total folate in beef liver and green peas extracted with pH 4.9, 7.0, or 7.85 buffers indicated the superiority of the pH 7.85 buffer. In all experiments, the completeness of extraction was improved when the residue from the first extraction was suspended in a new portion of buffer and recentrifuged. These results support the superiority of the Wilson and Horne extraction buffer and indicate the need for a second extraction in the analysis of many foods and other biological materials.
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