Protein Quality


Protein Quality
Protein is essential for the normal body development and growth. Quality of proteins must be considered while taking a protein. The quality is usually based on the proportion of the essential amino acids present in a protein. The proteins that approach the ideal proportion of essential amino acids corresponds to human requirement and easily digestible are regarded as ‘good quality’ proteins. In this article, the discussion will be about that how to determine the protein quality.
Protein Quality determination:
The quality of a protein is determined by some biological tests that include:
Biological Value (BV)
Protein Efficiency Ratio (PER)
Net Protein Utilization (NPU)
Chemical score
Biological value:
It is the amount of absorbed protein retained in the body. Biological value is also expressed as the co-efficient of protein nitrogen retention. It measures how efficient the protein is being utilized by the living body. When the amino acids in the food that we take responds to the complete body protein requirement, almost all nitrogen is retained and the biological value is very close to 1.0 that is the maximum ratio of biological value. When nutritional quality of protein dwindles down, the biological value is also lowered because less nitrogen is retained. Some foods have the following biological values:
Whole egg 0.95 (BV)
Milk whey 0.95
Gelatin 0.0
Meat and fish 0.75
Protein efficiency ratio (PER):
It is another biological parameter for measuring the protein quality. Protein efficiency ratio is the ratio between the weight gain and protein consumed. It measures the effectiveness of a protein through the measurement of animal growth. Animals e.g rats are fed with ad libtum containing 8 or 10% protein for 28 days and then their weight and amount of protein eaten are recorded. The recorded value of protein is then compared to the standard of 2.7, which is standard value of casein protein. The protein exceeding the ratio of 2.7 is considered of high quality. The protein energy ratio of some foods is:
Egg 3.92 (PER)
Fish 3.55
Rice 2.18
Whole wheat bread 1.10
Cow’s milk 3.09
Net protein utilization (NPU):
Net protein utilization is similar to the biological value but it involves a direct measure of retention of absorbed nitrogen. It is in vivo method for determining the protein amount in food retained by body for growth. Net protein utilization and biological value both measure the same parameter of nitrogen retention, however, the difference is in that side the biological value is calculated from nitrogen absorbed whereas net protein utilization is from nitrogen ingested.
NPU can be calculated as:
NPU= BV*digestibility
Chemical score:
It involves the concept of comparison of a specific protein with a standard protein such as egg protein that has 1.0 maximum biological value. In this comparison, the ratio of essential amino acids is considered and compared with the reference protein. Chemical score is the ratio between the quantity of most limiting essential amino acid in the test protein to the quantity of same amino acid in egg protein.
So, in a nutshell, the protein quality can be determined by the biological tests and we must include high quality protein in our diet having high BV and NPU.

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