Mar. 24 ,1933 
Determination of Starch Content 
1005 
PURIFICATION OF DEXTROSE) SOLUTION AND DETERMINATION OF DEX¬ 
TROSE BY COPPER REDUCTION 
Cool and, in the case of linseed meal or other material yielding solutions 
which at this stage need further purification, add not more than 1 cc. 
of a 10 per cent solution of phosphotungstic acid in 1 per cent hydro¬ 
chloric acid. Mix and allow to stand for 15 minutes at least. Increase 
the volume with water to 250 cc. in a volumetric flask, mix well, and 
filter through dry paper. Partially neutralize 200 cc. of the filtrate 
while stirring by adding 10 cc. of a heavy solution of caustic soda (44 gm. 
of sodium hydroxid per 100 cc. of the cooled solution) and nearly com¬ 
plete the neutralization with a little powdered sodium carbonate. 25 
Transfer to a 250 cc. flask with water, cool to room temperature, make 
up to the mark, and mix well. Filter, if necessary, and determine the 
dextrose in a 50 cc. aliquot of the filtrate, by copper reduction, employing 
the gravimetric method either of Munson and Walker or of Allihn. 
Correct the weight of dextrose obtained by the weight of dextrose 26 
found for the same aliquot of the malt control, and multiply the corrected 
weight of dextrose by 0.90 to obtain the weight of starch. (This factor 
0.90 represents the theoretical ratio between starch and dextrose and 
was used throughout this study, although several other investigators (r, 
/>. 95) have shown that the factor 0.93 more nearly represents the actual 
yield.) 
AEIQUOTS 
or, 
Charge X 
200 200 50 
-X-X-; 
500 250 25O 
Charge x 0.064. 
SUMMARY 
A method for the accurate determination of the starch content of 
material containing interfering polysaccharids is needed as an aid in the 
examination of impure linseed meals, apple products, and other sub¬ 
stances containing important quantities of mucilage, pectin, or car¬ 
bohydrates of that character. 
Linseed meal is sometimes adulterated with weed seeds and other 
impurities. Unless these impurities are present in excessive quantities 
it is impossible to demonstrate such sophistication by the usual chemical 
analysis. The pure seed of the flax plant, however, contains no starch. 
As the nonflax material normally associated with flaxseed would con¬ 
tain no more than 50 per cent of starch, and the allowable limit of such 
nonflax material is 6 per cent, 27 any linseed meal containing more than 
3 per cent of starch may be held to be adulterated. 
The interfering polysaccharids are a serious obstacle to a correct 
determination of starch. Plant mucilages when moistened are prac¬ 
tically impervious to water or weak alcohol. This prevents the leaching 
out of sugars by these solvents. Unless the mucilages and pectins, 
which are polysaccharids, are eliminated before the acid hydrolysis, 
* 5 Anhydrous carbonate is preferable, as it dissolves rapidly. 
58 In the official A. O. A. C. diastase method (/) the direction to "correct the weight of reduced copper" 
by that found in the malt blank is wrong. 
* 7 None of this 6 per cent shall be deliberately added. 
