This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Dextrose or glucose, for it is known by both names, is widely distributed in fruits, honey, and some vegetables. The sugar known by the trade name "Cerelose" is practically a pure crystalline dextrose and is made from corn. The term dextrose or glucose should be applied to crystalline dextrose or its solution. Commercial corn sirup has been incorrectly called glucose. It is made from corn, the starch being hydrolyzed with acid. Hydrolysis is carried to the point at which 40 to 50 per cent of the starch is changed to sugar, the remainder being split into dextrins. The sirup contains both dextrose and maltose, but for convenience the sugar is usually all determined and expressed as dextrose. Thus corn sirup is a mixture of dextrin, maltose, dextrose, and water.
Levulose or fructose is also widely distributed in natural foods, often accompanying dextrose, or dextrose and sucrose. At present, pure crystalline levulose is expensive. Honey contains nearly equal parts of dextrose and levulose. When honey crystallizes, the greater part of the levulose is in the sirup and the dextrose in the crystals.
Sucrose is widely distributed in plants, often with dextrose and levulose. The common sources of it commercially are the sugar beet, the sugar cane, the sugar maple, and the sugar palm. It is the common granulated sugar on the market and is practically pure whether obtained from the beet or cane. Maple sugar is not purified, for it would then lose the flavor for which we prize it.
Maltose is formed as an intermediate product when starch is hydrolyzed by boiling with mineral acid in the manufacture of commercial corn sirup from corn. Commercially it is prepared from starch by a diastatic enzyme and it is also found in germinating cereals and malt products.
Lactose is obtained from milk. One of its uses is for infant feeding.