Blog
July, 2021

Protein quality assessment methods

Consumers’ attention to the products they buy has changed over the years, with an increasing focus on local and quality ingredients. This trend pours into the realm of plant-based products as well, with a preference for those containing fewer ingredients, using quality plant-based proteins.

But what exactly does it mean for a protein to be of good quality?

According to the article “Plant Proteins: Assessing Their Nutritional Quality and Effects on Health and Physical Function”  there are at least two basic requirements that a protein must have to be considered as quality, or complete, for human nutrition. The presence of the amino acids essential to human growth and development, and the ability to be easily digested and absorbed.

But how can we establish the presence of these two requirements?

There are several indicators that allow you to measure them, and these can vary in different parameters, depending on the type of information you want to get. Among these, we can mention the biological value (BV), the protein efficiency ratio (PER), the net protein utilization (NPU), the PDCAAS (Protein Digestibility Corrected Amino Acid Score) and the DIAAS (Digestible Indispensable Amino Acid Score).

According the article  “Protein – Which is Best”, Biological Value (Biological Value BV) is one of the most widely used indicators of protein quality. Biological value provides a measure of how efficiently the body uses the protein consumed in the diet. This index measures the quality of protein by calculating the nitrogen in the protein used for tissue formation divided by the nitrogen absorbed from food, taking as a reference value the egg, which has a biological value of 100.  A second approach is the Net Protein Utilization (NPU), and evaluate the quality of proteins according to the amount of introduced nitrogen that is retained by the body.

The Protein Efficiency Ratio (PER) on the other hand is based on the weight gain related to the amount of protein taken in a given period. In this case, the reference value is established by high protein sources such as milk protein (3.1) or casein (2.9).

These three are biological methods, and are based on the direct or indirect measurement of protein deposition or body weight gain that the protein or protein mixture analyzed is capable of promoting, while also considering its digestibility.

The Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a way The PDCAAS was adopted by the U.S. Food and Drug Administration (FDA) and the Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO) in 1993 as the preferred method for assessing the quality of a protein.

The PDCAAS compares the amino acid content of a test protein (mg/g protein) to a theoretical reference protein believed to meet the amino acid requirement (mg/g protein) for the fecal-based digestibility rate, creating a ratio known as an amino acid or chemical score. In general, most animal proteins, have a PDCAAS, or amino acid score, near 1.00, and are generally considered to be complete sources of protein for human development and growth. As for plant proteins, soy protein, for example, has a PDCAAS nearly equivalent to milk protein, while other plant proteins such as canola, potato and pea have a PDCAAS of around 0.75. However, even though they have a generally lower PDCAAS, it is easy to be able to get the right amount of protein from plant proteins by simply taking several of them in a complementary way even in larger amounts.

According to this study published in the British Journal of Nutrition, in order to overcome some limitations of the PDCAAS, in which if a protein exceeds the standard value of 1.0 it is considered equal to all proteins with a score of 1.0, the FAO has recommended the DIAAS (Digestible Indispensable Amino Acid Score) method as an alternative index to evaluate protein quality. PDCAAS calculates the digestibility of a protein by looking at the levels of protein remaining in fecal matter, while DIAAS rates digestibility from the end of the intestine (or ileum) to provide a more accurate measure.

Were you familiar with these methods of analysis?

These indicators can be very interesting for producers of food products that contain plant proteins, as they are required to develop products that are digestible for a balanced diet.