Fundamentals of Food Technology

Quality and bio assay of protei

Quality of Proteins

It is evident that the nutritive value of proteins will depend on the essential amino acids composition.
Quality of protein is affected by the amino acid content, amino acid imbalance, interference of non available carbohydrates and trypsin inhibitors and influence of heating and processing.

Biological Assays
In this method the Digestibility Coefficient (DC) and Biological Value (BV) of the protein can be determined using rats or humans. Protein digested is expressed in terms of ‘digestibility coefficient’.

DC = Protein intake (g) – protein lost in digestion (g) × 100
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Protein intake
The term BV. refers to the percentage of digested protein utilized by the body.

BV = Protein digested (g) – protein lost in metabolism (g) × 100
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Protein digested (g)


Net Protein Utilization (NPU)
The net protein utilization takes into account the losses in digestion and metabolism. It is calculated by the following formula.

NPU = (Digestibility coefficient × Biological value) / 100


Net Protein Ratio (NPR)
The net protein ratio is calculated by adding the loss in weight of the control group to the gain in weight of the test group and dividing the total weight (g) by the quantity of protein consumed by the test group

NPR = Gain in weight (g) of the test group + loss in weight (g) of the non protein group
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Protein intake (g) of test group


Protein Efficiency Ratio (PER)
This method measure the ability of protein to promote the growth. PER is expressed as gain in weight of albino rats for every gram of protein consumed. Protein efficiency ratio (PER) as follows

PER = gain in body weight (g)
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Protein intake (g)


Chemical score
The chemical scoring is one of the easiest methods if appropriate instruments for measuring amino acid content of a protein are available. The chemical score for a protein is arrived at by determining the most limiting amino acid for that protein by comparing it with standard protein like hen’s egg protein.

Amino acid score = mg amino acid/ g test protein
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mg amino acid/ g reference protein

Information on the most limiting amino acid, is generally sufficient to arrive at the chemical score.

Supplementary / complementary value of proteins
If the protein of the diet is seriously deficient in one or more of the essential amino acids, nitrogen equilibrium cannot be sustained, no matter how complete and excellent the diet may be in other respects.

If, however, another protein containing the missing amino acids in adequate amounts is added to the diet, nitrogen equilibrium and normal nutrition can be established.

This capacity of proteins to complement and supplement each other is known as complementary or supplementary value.