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The Effect of Heat Upon the Biological Value of Meat Protein

Laboratory of Household Science, University of California, Berkeley

1. The biological value for maintenance of raw beef muscle protein at 7 per cent level tested on rats was found to be greater than that of the same meat cooked in three different ways. The figure for the raw beef is 67, for that boiled at ordinary pressure, 60 (to internal temperature of 85°C.), boiled for 7 minutes at 15 pounds' pressure, 62 (to internal temperature of 85°C.), boiled for 1 hour at 15 pounds' pressure, 56. There appears to occur a heat injury to the protein increasing in severity with the length of exposure and the height of the temperature reached.

2. Young rats were fed these rations for 6 weeks and were found to grow best on the raw beef diet. The gain in body weight per gram of protein eaten was 2.58 ± 0.04 on the raw beef, 2.41 ± 0.06 and 2.44 ± 0.06 on the boiled and autoclaved 7 minutes' preparations and 1.80 ± 0.05 on that autoclaved 1 hour. The food intake was slightly larger on the raw diet than on the other three but not sufficiently to account for the extra growth seen.

3. Horseflesh prepared raw and autoclaved for 1 hour by similar methods was fed at 5 and 6.8 per cent levels in the same basal diet to young rats. The total intakes on these diets were in all cases considerably larger than on the beef diets but at a comparable level the gain in weight of the rats in 6 weeks per gram of raw horseflesh protein eaten was similar to that for beef, 2.68. The autoclaved horseflesh yielded a higher value than the similar beef, 2.21 as compared with 1.80, due perhaps to poorer heat penetration in the former.

4. Attention is drawn to the discrepancy between the high values for growth of the beef protein, parallel with the best values obtained on other animal proteins, and the lower values for maintenance shown by the biological values, parallel with casein and the cereal proteins. This may be due to sharp differences between the mechanisms of the endogenous protein metabolism of growth and maintenance.