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The Estimation of Carbohydrates. IV.: The Presence of Free Pentoses in Plant Extracts and the Influence of other Sugars on their Estimation

Published online by Cambridge University Press:  27 March 2009

William A. Davis  and
George Conworth Sawyer
William A. Davis
Affiliation:
(Rothamsted Experimental Station.)
George Conworth Sawyer
Affiliation:
(Rothamsted Experimental Station.)
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Extract

Evidence is brought forward to show that free pentoses exist in the alcoholic extracts of foliage leaves of different plants. Their amount can be estimated with a fair degree of accuracy by the ordinary distillation process or by the reducing power of the purified liquor after other sugars have been fermented away.

When, however, small amounts of pentose have to be estimated accurately in presence of large quantities of other sugars, it is advisable, as suggested by Kluyver, to ferment away these sugars before applying Kröber's process.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 6 , Issue 4 , December 1914 , pp. 406 - 412
Copyright
Copyright © Cambridge University Press 1914

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References

page 406 note 1 J. Agric. Science, 1913, V. 465.Google Scholar

page 407 note 1 Matignon, , Bull. Soc. d'Encouragement, 1914, CXXI. 445.Google Scholar

page 407 note 2 loc. cit. p. 460.

page 407 note 3 Biochemische Suikerbepalingen, Leiden, 1914, pp. 181 and 190.Google Scholar

page 408 note 1 A large number of experiments, details of which will be published later, have shown that baker's yeast does not ferment or assimilate the pentoses (xylose and arabinosc); on the other hand the maltase-free yeasts (S. Marxianns, S. exiguus and S. anomalus) gradually but slowly destroy these sugars.

page 409 note 1 Daish, J. Agric. Sci. 1914, VI. 255.CrossRefGoogle Scholar

page 410 note 2 Compare Gunther, Gölt. Dissert. 1891, p. 19.

page 410 note 3 Cp. Kruger, Rostock Dissert. 1895, p. 29.

page 410 note 4 Zeit. Zuckerind Böhmen, XXIII. 291.Google Scholar

page 410 note 5 Zeit. angew. Chem. 1902, 508.

page 410 note 6 A necessary precaution in the estimation of pentoses and pentosans which is not emphasized in the standard text-books is that the distillation flasks should be fitted with rubber stoppers and not with ordinary corks. The latter are invariably attacked by the hydrochloric acid and give appreciable quantities of furfural. The following example shows this. A series of “blanks” was carried out with hydrochloric acid in a flask fitted with ordinary corks. The results were as follows: 1st distillation gave 0·0022 phloroglucide; 2nd distillation gave 0·0042; 3rd distillation 0·0045; 4th 0·0035; 5th distillation gave 0·0013 grm. phloroglucide. When similar distillations were made in a flask fitted with rubber stoppers there was no change of colour after adding the phloroglucinol and the weight of phloroglucide obtained was nil.

page 412 note 1 loc. cit.

page 412 note 2 Davis, and Daish, , J. Agric. Sci. 1913, V. 465.Google Scholar