Experimental cookery

Heat coagulation. As has been indicated heat coagulation of proteins is used in preparation of food products, and, fortunately for the mental equilibrium of the cook, heat coagulation of proteins is ordinarily not reversible. Otherwise, many cooked dishes would, with certain treatment, revert to their original uncooked consistency. Some of the changes occurring during heat coagulation of the proteins have been indicated. But these are not the only factors playing a role in the process. Electrolytes have some role in heat coagulation of proteins. This is shown in the work with distilled water egg custards. It has been shown that, if the mineral content of egg white is lowered through dialysis, 20 RELATION OF COOKERY TO COLLOID CHEMISTRY coagulation does not occur on heating. The effect of electrolytes in heat coagulation may be brought about either by chemical reaction or by adsorption. If the effect of salts is brought about by adsorption, the salts must be very strongly adsorbed and almost impossible to remove from the aggregated protein by washing the protein, for the process is usually irreversible. Any theory of heat coagulation of the proteins must not only explain how the proteins are rendered insoluble by heat but the effect of other factors. That the heat coagulation of proteins is influenced by electrolytes, sugar, temperature, time, the reaction of the solution, and the presence of water and other factors is evident when the cooking of eggs, custards, salad dressings, cheese and egg dishes, baked products, and meat is observed. The effect of some of these factors can be determined in the laboratory; but the understanding of the manner of their action is lacking in many instances and awaits explanation by the colloid chemist or bio- chemist. Bancroft and Rutzler have reported that heat-coagulated egg white may be peptized by dextrose and certain salts. They showed that the coagulated and repeptized egg-white sols are identical with the original solution by immuno-biological tests for species specificity and isoelectric point measurements. Because of the similarity of the reversed protein to the original protein they believe that coagulation is a colloidal reaction which is due to a physical rather than a chemical change. Interfacial denaturation. Proteins are also denatured at interfaces, typical examples being the insoluble portion of beaten egg white, and froth or foam on milk. When egg white or milk foams are allowed to remain undisturbed, they gradually collapse and the wrinkled membranes, skin, or films may be observed through the microscope. Mention has already been made that protein can be recovered from a solution by removing the foam. Denaturation of protein solution occurs by shaking and in some instances spontaneously, an example being the membrane formed at the interface of an air/protein solution when no agitation has occurred.