DEXTRINS 165 



maltose until the amount present again attains the value 80 

 per cent, which is the normal maximum ; this experiment, 

 which is due to Brown and Morris,* shows that the non-maltose 

 is composed of different constituents, some of which are con- 

 verted into maltose by diastase more readily than others ; 

 moreover, experiments have shown that these substances behave 

 differently towards yeast, some being more readily fermentable 

 than others. This non-maltose constituent represents a mix- 

 ture of the various dextrins mentioned above as having been 

 described by several authors. 



General Properties of Dextrins. 



From what has been said above, it will be seen that the 

 term dextrin comprises a number of substances some of which 

 are not at all well defined. The following may, however, be 

 regarded as approximately representing the characteristics of 

 all substances included in this group : — ■ 



1. They are amorphous substances which are readily soluble 

 in water to form gummy solutions, which are used as a sub- 

 stitute for natural gum ; they are precipitated from aqueous 

 solutions by the addition of alcohol. 



2. Dextrins in strong solution give a precipitate with 

 basic lead acetate. 



3. As their name implies, they are strongly dextro-rotatory, 

 in which respect they resemble starch. 



4. They give either a red colour or no colour at all with 

 iodine, 



5. They are not fermentable by yeast alone, but are fer- 

 mented by a mixture of yeast and diastase acting together, 

 which is no doubt due to their slow hydrolysis in the first 

 place by the diastase and the subsequent fermentation of the 

 maltose so produced. 



6. They do not reduce Fehling's solution when pure. 



7. They are converted into glucose on hydrolysis with 

 mineral acids. 



As has already been mentioned, starch when suddenly 

 heated to about 200° is converted into a substance commercially 

 * Brown and Morris : " J. Chem. See, Lond.," 1SS5, 47, 527. 



