DEXTRINS 163 



The following method for the estimation of starch in barley 

 is due to Horace T. Brown * : — 



Five grams of the powdered or crushed grain are extracted 

 for three hours in a Soxhlet extractor with alcohol (sp. gr. 

 0-90) ; the residue is then thoroughly boiled with lOO c.c. of 

 water, and, after cooling to 57°, 10 c.c. of active malt extract 

 are added and the mixture is set aside for one hour ; it is 

 thereupon boiled and filtered into a flask with a 200 c.c. 

 graduation mark ; the residue is thoroughly washed with 

 water, and, after cooling, the filtrate and washings are made 

 up to 200 c.c. The cupric reduction of 20 c.c. of the solution 

 is determined under the conditions laid down by Brown, Morris, 

 and Millar,t the maltose being calculated according to Table 

 XI in that paper [loc. cit., p. 100), after correction for the re- 

 duction due to the malt extract. The starch equivalent to 

 this maltose is then ascertained by assuming that 84-4 parts 

 of maltose correspond to lOO parts of starch. 



The malt extract is prepared by digesting 10 grams of 

 fresh finely-ground malt for two to three hours with 200 c.c. 

 of water and filtering. 



A method of starch estimation due to von Fellenberg f 

 depends on the solution of the starch in a hot solution of 

 calcium chloride, its precipitation by iodine and the decom- 

 position of the iodine precipitate by alcohol. 



DEXTRINS. 



The term dextrin is applied to substances which are 

 formed from starch by the action of heat alone or of diastase 

 or mineral acids. 



Occurrence. 



In the plant dextrins may occur as transitory substances 

 whenever starch is being acted upon by diastase ; further, 

 certain dextrins may occur in a more permanent form. Thus 

 the sap of the epidermal cells of Arum italicum turn reddish- 

 violet on the application of iodine. The aqueous extract of 



* Horace T. Brown : " Trans. Guiness Research Lab.," 1903, i, 89. 

 t Brown, Morris, and Millar : " J. Chem. Soc, Lond.," 1897, 71, 94- 

 t V. Fellenberg: " Mitt. Lebensm. Hyg.," 1916, 7, 369. 



II* 



