This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Wheat and flour contain many enzymes, some of which are important because of their action during fermentation of cracker and bread doughs. Others become active in the sprouted grain, hence affect bread making only rarely when some sprouted grain is included with sound wheat in milling. Of the numerous enzymes, the diastases or amylases and the proteinases are the most important from the standpoint of baking.
Diastases. Andrews and Bailey state that the chief function of the starch enzymes of wheat and flour is changing starch to sugars. In sound normal wheat and flour the diastatic activity is due primarily to the action of beta-amylase. When wheat germinates, a second "diastatic factor," termed alpha-amylase, is produced. Accompanying the activation of alpha-amylase are the phenomena of dextrination and liquefaction. Both amylases convert starch to reducing sugars, the alpha-maltase yielding alpha-maltose and the beta-amylase producing the corresponding beta sugar. The maximum activity of beta-amylase occurs at pH 4.5 to 5.1, whereas that of alpha-amylase is at pH 5.6 to 5.8.
Proteinases. Until lately little was known about the proteolytic enzymes of flour except that they brought about hydrolysis of flour proteins. Balls and Hale have not only reported a method for estimating the proteolytic enzymes in flour but also the action of these enzymes. They state alteration of flour that takes place in bleaching and storage in air is due to a diminution of the proteolytic activity, brought about by the oxidation of the activator of the flour proteinase. JØrgensen states that wheat flour contains powerful proteolytic enzymes which are usually latent but activators such as glutathione or yeast-water stimulate these proteinases of flour. Such sub-stances as KBrO3 and ascorbic acid, because they depress the activity of the proteinase, have been found to be good improvers of baking strength of wheat flour. JØrgensen has applied for a patent in the United States for such a use of ascorbic acid.