The Nutritional Effects of Heat on Food Proteins, with Particular Reference to Commercial Processing and Home Cooking

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Abstract
The effect of heat as applied to food products during commercial processing and home cooking on the nutritive value of the food proteins for the growing rat has been studied on a number of foods by the nitrogen balance method developed in this laboratory. The samples compared were unheated, or very mildly heated as in a solvent-extraction method, and heated to high temperatures by autoclaving in the laboratory (sunflower seed meal), subjection to oil extraction by the expeller process (peanut and linseed meals) or the hydraulic process (cottonseed flour), or subjection to a process of flaking and toasting (corn). As an example of home cooking, the effect of a standard method of roasting on the proteins of beef was ascertained. In all cases, the unheated or mildly heated sample and the highly heated sample were obtained from the same raw material. During these heating processes the digestibility of the proteins of sunflower seed meal, cottonseed flour and corn was definitely decreased by amounts ranging from 2.5 to 14.2 percentage units. The biological value of the proteins of peanut meal, sunflower seed meal, and cottonseed flour was also definitely decreased in these processes. The percentage of total heat damage was highest for corn (20) and peanut meal (18), intermediate for sunflower seed flour (10) and cottonseed flour (11); no heat damage was demonstrated in the roasting of beef. For flaxseed (linseed), heat exerted a favorable effect on protein utilization (7%), especially evident in improved protein digestibility. The heat processes studied always decreased the thiamine content of those foods subjected to assay, but the pantothenic acid content was not impaired in the peanut meals judged by an assay method that does not measure the amount of the vitamin contained in coenzyme A.