The glucose of commerce, which may be regarded as a mixture of grape sugar, maltose and dextrins, is prepared by hydrolysing starch by boiling with a dilute mineral acid.
Saccharomyces Marxianus will not hydrolyse maltose, but it does attack cane sugar and ferment the products of hydrolysis.
Of especial note is the transformation of maltose by maltase into glucose, and of cane sugar by invertase into a mixture of glucose and fructose (invert sugar); other instances are: lactose by lactase into galactose and glucose; trehalose by trehalase into glucose; melibiose by melibiase into galactose and glucose; and of melizitose by melizitase into touranose and glucose, touranose yielding glucose also when acted upon by the enzyme touranase.
The hexoses so obtained are not necessarily identical: thus cane sugar yields d-glucose and d-fructose (invert sugar); milk sugar and melibiose give d-glucose and d-galactose, whilst maltose yields only glucose.
By acting with hydrochloric acid on glucose Fischer obtained isomaltose, a disaccharose very similar to maltose but differing in being amorphous and unfermentable by yeast.