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Methods of Estimating Carbohydrates II. The Estimation of Starch in Plant Material: The use of Taka-diastase

Published online by Cambridge University Press:  27 March 2009

William A. Davis  and
Arthur John Daish
William A. Davis
Affiliation:
(Rothamsted Experimental Station.)
Arthur John Daish
Affiliation:
(Rothamsted Experimental Station.)
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Extract

1. The Sachsse method of estimating starch is unreliable in the case of plant material; not only does the presence of pentosans falsify the results as pentoses are formed during the hydrolysis, but actual destruction of dextrose occurs during the prolonged treatment with dilute acid.

2. O'Sullivan's method gives low results owing to the loss of dextrin which occurs during the purification of the solution after the conversion by diastase.

3. A method is described for estimating starch based on the use of taka-diastase; under suitable conditions this converts the starch into maltose and dextrose only and no loss of these sugars occurs when the solution is treated with clearing agents such as basic lead acetate.

4. The necessity of removing substances soluble in water, such as gums, etc., which are optically active and thus cause error in the estimation of starch in plant material is emphasised. Special care is also necessary in sampling.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 6 , Issue 2 , May 1914 , pp. 152 - 168
Copyright
Copyright © Cambridge University Press 1914

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References

page 152 note 1 We have found in a series of analyses made by this method of purified potato starch dried in vacuo at 120°C. (see p. 167), results varying from 93·8 to 94·3% of starch, whereas by the ordinary diastase method an average result of 100·1% (see p. 165), and with taka-diastase an average result of 99·6% was obtained with the same sample. That actual destruction of dextrose occurs on prolonged heating with dilute acid we have recently shown (Journ. of Agric. Sci., 1913, 5, p. 437CrossRefGoogle Scholar). This destruction of dextrose is a source of error in all the methods which make use of hydrochloric acid to effect hydrolysis, such as that of Märcker and Morgen, even when the primary conversion of the starch has been carried out with diastase.

page 153 note 1 When basic lead acetate is added to the solution obtained by the diastase conversion of purified starch not the slightest precipitate is produced with the dextrin existing in solution; but the results given on pp. 165–167 show that if sodium carbonate is subsequently added, or hydrogen sulphide is passed so as to precipitate the lead, a greater or smaller proportion of the dextrin is removed by co-precipitation.

page 153 note 2 In 1898 Stone, and Wright, (J. Amer. Chem. Soc. 20, 639–647)CrossRefGoogle Scholar attempted to estimate starch by means of taka-diastase; but as they assumed maltose to be the only sugar formed and measured the products of the action solely by the reducing power without reference to their rotation, it is not surprising that they concluded that under their conditions “taka-diastase is not adapted for use in the quantitative estimation of starch.” It will be seen that we have come to an exactly opposite opinion.

page 154 note 1 We have used the commercial product manufactured by Messrs Parke Davis & Co.

page 154 note 2 Applying Meissl's temperature correction to the value obtained by Brown, , Morris, and Millar, (Trans. Chem. Soc., 1897, 71, p. 112Google Scholar) as the specific rotatory power of pure maltose.

page 163 note 1 That this was the case was found not only by analysis but by microscopical examination by the chloral hydrate-iodine method; even the guard cells were free from starch.