Experimental cookery

Bungenberg de Jong states that gliadin is a protein that swells easily in water, is readily peptized to a colloidal solution by dilute alkali or acid and in water forms a sticky mass that can easily be stretched into threads. Glutenin in water is a flaky mass without much coherence which swells in, but is diflficult to peptize in dilute acid. It peptizes easily in alkali. Bungenberg de Jong suggests that the plastic and elastic properties of gluten are partially due to the two proteins' adhering to each other because of opposite charges throughout a definite pH range. If this is true, he says that at the pH at which the charge on each protein is the same either a maximum or minimum in physical properties should occur, i.e., turbidity, coherence, farinogram curves (which is a measure of consistency of the dough). The point at which this maximum occurs might be altered by the presence of other proteins, such as albumin and globulin with isoelectric 418 FLOUR AND BREAD points much lower than that of glutenin, hence would be negatively charged at the pH range at which the gliadin-gluten complex occurs. He also discusses the possibility of salts altering the maximum point. Jong represents this maximum or minimum range schematically. See Fig. 44. Gliadin, below its isoelectric point pH 6.4, is positively charged, this charge increasing as the pH is lowered. However, about pH 5.6, the isoelectric point of glutenin, the glutenin is negatively charged. In Bungen- berg de Jong's experiments maximum turbidity occurred at pH 6.1. Gluten quality and proteolytic enzymes. Balls and Hale ascribe part of the quality of gluten to the action of the proteolytic enzymes. They state that the proteolytic enzymes change the colloidal character of wheat proteins, the effects of which are shown in the gluten. "Proteinases usually Fig. 44. — Bungenberg de Jong's representation of effect of charge on gliadin and glutenin on gluten properties. The charge of components is represented by posi- tive and negative signs. J. Soc. Chem. Ind. 52: 391T, 1933. produce first a coagulation of the protein ; later the coagulated material Is broken down and perhaps ultimately dissolved. If this rule holds for flour, in the first phase of proteinase action the gluten would probably become more tenacious; in the second phase it would be broken down to a thinner, more nearly liquid material." They add that a small amount of proteinase may be beneficial, a larger amount harmful. "Usually there is too much, rather than too little." The baking qualities of gluten are determined largely by Its hydration capacity, its power of cohesion, and its elasticity. The hydration capacity results in a larger or smaller volume when mixed with water. With a larger volume the particles of the gluten form a greater surface for con- tact with each other, thus increasing the sponge-like character of the dough. Also with increased swelling the gluten becomes more tender and less tenacious ; with less swelling the volume is smaller but the tenacity may be greater. The swelling can be so great that there is a limit to the HYDRATION CAPACITY 419 amount of stretching the gluten will stand before breaking. The cohesive- ness of the gluten gives less chance for the gluten particles to be pulled apart ; the elasticity permits stretching under pressure or when pulled.