The estimation of sugars in the leaf of the mangold (Beta vulgaris)

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Abstract
Fructose and sucrose may be estimated in unclarified extracts of the mangold leaf by a modification of the Harding and Downs iodide-free copper reagent. Fructose is determined after oxidation of glucose by hypoiodite and sucrose as the increase in reducing power after treatment with invertase. Errors of estimation in unclarified extracts fall entirely on the glucose fraction, which is only correctly determined after clarification with dibasic Pb acetate, or as the difference in the values obtained before and after treatment with yeast. The precipitates formed by dibasic Pb acetate are complex acetates somewhat soluble in water and completely soluble in excess of the reagents. The solubility increases with the content of acetate, and the use of a dibasic Pb acetate and rather conc, extracts is recommended for efficient clarification. Loss of fructose under these conditions is unavoidable, and this sugar must be separately determined in unclarified solutions. To avoid loss of glucose solutions must not be neutralized before adding basic Pb acetate. Charcoal may be used with caution as a clarifying agent in special circumstances while the use of yeast gives a rapid and accurate method of determining glucose. Ferricyanide reagents are found much less suitable for application to plant extracts than Cu reagents. If extracts are relatively rich in substances other than sugar they should be analyzed only after considerable dilution. Tests were made for raffinose, maltose, galactose and pentose by selective fermentation. None of these sugars occurred in amts. large enough for detection by the methods employed.