THE EFFECT OF HIGH TEMPERATURES ON THE NUTRITIVE VALUE OF FOODS.

Transcription

1 THE EFFECT OF HIGH TEMPERATURES ON THE NUTRITIVE VALUE OF FOODS. BY ALBERT G. HOGAN. (From the Department of Chemistry, Kansas Agricultural Experiment Station, Manhattan.) (Received for publication, March 17, 1917.) In an earlier publication1 from this laboratory results were cited which indicated that young rats are unable to grow on a diet that has been subjected to high temperatures. Many investigators believe that the so called accessories are destroyed by exposure to heat, and as that is a point of great importance, further studies were made on the nutritive properties of heated foods. In these investigations white rats were used as experimental animals. Many of them were at least half grown when the feeding trials began, but some were quite immature. In some cases corn constituted the ration, in others a mixture of corn and egg white, one or both of which had been heated in an autoclave. In every case a salt mixture was added to the diet to compensate for the mineral deficiencies of maize. The heating process was continued for 6 hours at 30 pounds pressure. It soon became evident that heating the egg white had little or no effect; but in every case in which the corn was heated, the diet was inadequate in some respect, and the animals were unable to maintain their body weights. These facts are presented in greater detail in Charts 1 to 4. It has been suggested, however, that some factor other than that of accessories was altered. If such were the case probability seemed to indicate that the protein of the ration had been changed in some way. In order to investigate that point, a comparatively pure protein, egg white, was heated in an autoclave for 6 hours at 30 pounds pressure. This was carefully dried, and combined 1 Hogan, A. G., J. Biol. Chem., 1916, xxvii,

2 116 High Temperature and Food Values with protein-free milk, butter, starch, and agar, in such proportions that the protein formed approximately 9 per cent of the ration. This diet did not permit maximum growth and possibly these rats grew somewhat more slowly than other animals receiving a similar ration in which the protein had not been heated. Evidently, however, the nutritive value of the protein had not been seriously impaired. A series of feeding trials similar to the one just described was conducted with casein in the ration instead of egg white. In these experiments the casein was heated in an autoclave for 2 hours, but at different pressures. In one case the protein was heated at 15 pounds, in another at 30 pounds, and in a third at 45 pounds pressure. A control lot received unheated casein. In this series the protein formed approximately 12 per cent of the ration. In all cases animals of the same sex grew at approximately the same rate, indicating that the nutritive value of the casein had not been materially lowered by the high temperature. The data are presented graphically in Charts 5 to 9. SUMMARY. The heating process described in this paper does not materially lower the nutritional value of protein. It is suggested that one or more of the so called food accessories may be injured by high temperatures.

3 Albert G. Hogan 117 CHART 1. The animals shown in this chart received as their sole diet corn that had been heated in an autoclave. All of them slowly lost weight, and Rat 22 died. To show that rats are able to grow on corn that has not been heated, some additional curves are reproduced here. The bioken lines representing Rats 181 and 183 are typical of a fairly large number that have grown practically to maturity in this laboratory on corn alone (that had not been heated). 5 at the end of a curve indicates the animal s death.

4 118 High Temperature and Food Values CHART 2. The animals shown in this chart received a diet similar to the one fed to the rats in Chart 1. This ration contained a much larger percentage of protein, however. Enough of the autoclaved egg white was added to make the protein content of the diet approximately 20 per cent. The younger animals failed to grow and finally died. During the experimental period the older animals steadily lost weight. x at the end of a curve indicates the animal s death.

5 CHART 3. These animals received corn that had been subjected to high temperatures. In addition they received unheated egg white, in amounts comparable to that given to the rats shown in Chart 2. The two younger animals grew slowly for a time, but finally died. Of the two older rats, the male made some gropth, but the female gradually lost weight. 5 at the end of a curve indicates the animal s death. CHART 4. The diet received by these animals consisted of unheated corn and autoclaved egg white. All animals grew slowly, but at the usual rate for this ration. 119

6 High Temperature and Food Values CHART 5. The protein constituted 9 per cent of the ration in this case, and consisted of egg white instead of casein. The egg white had been heated in the autoclave for 6 hours at 30 pounds pressure. The broken lines represent the growth of rats on a similar diet, in which the egg white had not been heated. The composition of the ration was as follows.!jm. Egg white Protein-free milk Butter Starch Agar

7 Albert G. Hogan 121 CHART 6. The diet fed to the animals shown above included approximately 12 per cent of unheated casein. These rats serve as controls for Charts 7, 8, and 9. Of the males, Rat 157, and of the females, Rat 169 grew most rapidly, and for convenience their growth curves are inserted in the following charts. The ration is as follows. w. Casein..., Protein-free milk Butter...,,, Starch...,...,... 2:: Agar...,..._......

8 122 High Temperature and Food Values CHART 7. The protein in the ration of these animals had been heated in an autoclave for 2 hours at 15 pounds pressure. The broken lines show the growth of control animals, taken from Chart 6.

9 CHART 8. The casein used in preparing the diets of these animals had been heated at 30 pounds pressure for 2 hours. Evidently the nutritional value of the casein had not been impaired. Gm. / I CHART 9. These animals received casein that had been heated in the autoclave for 2 hours at 45 pounds pressure. As both of these animals were females, the curve of Rat 157, Chart 6, is omitted. 123

10 THE EFFECT OF HIGH TEMPERATURES ON THE NUTRITIVE VALUE OF FOODS Albert G. Hogan J. Biol. Chem. 1917, 30: Access the most updated version of this article at Alerts: When this article is cited When a correction for this article is posted Click here to choose from all of JBC's alerts This article cites 0 references, 0 of which can be accessed free at ml#ref-list-1