Protein rating is calculated in a two-step process. First, the Adjusted Protein Efficiency Ratio (PER) is determined, and then, this adjusted PER is used to determine the final protein rating.
Calculating Adjusted PER
The adjusted PER is calculated using this formula:
Adjusted PER = (PER of test food * 2.5) / PER of standard reference caseinExplanation:
- PER of test food: This is the Protein Efficiency Ratio of the food you are evaluating. It measures how efficiently the protein in that food is used for growth.
- 2.5: This is a constant used in the calculation to adjust the PER.
- PER of standard reference casein: Casein is a milk protein used as a standard for comparison. Its PER is a benchmark for protein quality.
Calculating the Protein Rating
The protein rating is found by applying the adjusted PER to a typical daily consumption of the specific food:
Protein Rating = Adjusted PER * grams of protein in a reasonable daily intake of the food.Example:
Let's say a food has a PER of 2.0, and the standard reference casein has a PER of 2.5.
- Adjusted PER Calculation:
(2.0 * 2.5) / 2.5 = 2.0
If a reasonable daily intake of this food contains 10 grams of protein, the protein rating would be:
- Protein Rating Calculation:
2.0 * 10 grams = 20
Summary Table
| Step | Calculation |
|---|---|
| Adjusted PER | (PER of test food * 2.5) / PER of standard reference casein |
| Protein Rating | Adjusted PER * grams protein in a reasonable daily intake of the food |
Key Considerations
- The protein rating is based on the protein efficiency of the food and how much protein is typically consumed.
- The standard reference casein ensures consistent protein quality comparisons.
- This method provides a way to rate the quality of proteins in foods in relation to a standard.
