Within the world of protein, the concept of protein quality is a vital one. It refers to everything from the digestibility of a given protein to its amino acid balance, absorption qualities and more, and is important for several reasons — and also may be measured in a couple different ways.

At Idaho Milk Products, we’re here to provide the very best selection of milk protein concentrate and protein isolate products to customers with varying needs, including those in sports nutrition, weight management, general nutrition and more.

Consumers have been aware of the need to add more protein in their diets but are often not educated in the nutritional differences between protein sources. Measurements of protein quality help to differentiate the nutritional level of these various protein sources so people can make better choices. Specifically, there are two evaluation methods for protein quality that are used today — one that’s a bit older, and another that’s only been around for about a decade. These are the PDCAAS and the DIAAS methods, and we’re going to go over both of them so you understand the ins and outs of each, plus which is likely better for most reporting needs.

PDCAAS Protein Quality Method

The older of these two protein quality testing methods, one that became the industry standard for protein testing in 1993, is known as the Protein Digestibility Corrected Amino Acid Score, or PDCAAS. This was the first system created to test protein quality that used both in vitro and in vivo methods, and it’s still in use today as a way of testing the quality of various proteins — including those found in dairy products.

The PDCAAS method works by comparing the amount of essential amino acids in a given food to a scoring pattern. This pattern is based on the essential amino acid requirements of a child within ages 2-5.

The highest possible PDCAAS value that any given protein can possibly achieve is 1.0, which is an indication that the protein provides at least 100% of all amino acids required in a given diet. All dairy proteins, including casein and whey, have PDCAAS values of 1.0. On the flip side, proteins like tree nuts, cooked beans and others tend to be a bit lower, closer to 0.5.

DIAAS Protein Quality Method

While the PDCAAS protein quality evaluation method does continue to have value and will still sometimes be used in certain applications today, it’s largely been replaced over the last decade or so by a different method. This method, known as Digestible Indispensable Amino Acid Score, or DIAAS, is newer and has quickly become the preferred way of measuring protein quality for many different reasons.

The DIAAS method involves determining the ratio of digestible amino acid content in a given food compared to the same amino acid in a reference pattern based on age-specific amino acid requirements. The lowest amino acid value is taken and multiplied by 100, converting the ratio to a percentage that represents the DIAAS rating for a given food. This test is typically run in pigs, which have a stronger biological similarity to humans than rats and other test subjects.

Generally speaking, protein quality within DIAAS will range within a few bands. Any score below 75% on this scale will typically have “no quality claim” attached to it, and will not be desirable from a protein quality standpoint. Scores from 75% up to 99% will cover good protein quality, while any score of 100% or more (this scale can reach well above 100%) is excellent or high protein quality.

Benefits of DIAAS Over PDCAAS

Again, as we noted above, there may be settings where both these metrics can be used today. However, most experts tend to favor DIAAS over PDCAAS, and this is for a few specific reasons:

• More optimal scoring method: One limitation of PDCAAS is the fact that its maximum score of 1.0 can only be reached by a single amino acid. In contrast, the DIAAS scale can reach well above 100% in some cases, meaning it provides a more accurate protein quality score. Within PDCAAS, proteins of the very highest quality will sometimes not be highlighted — they can only score 1.0, after all, and many others can be at or near this number despite not actually being as high-quality. Consider whey protein isolate as an example: Its PDCAAS score is 1.0, while the PDCAAS score of soy protein isolate is 0.98. Not much difference, right? But if you instead use the DIAAS scale, whey protein isolate’s score is 1.09, while soy protein isolate is 0.90 — and that’s a much more significant and notable difference.
• Sampling differences: In addition, PDCAAS samples come from the feces of animal test subjects, while the DIAAS sample comes from the ilium. The latter is a significantly more accurate representation of human digestion, meaning it provides a more accurate score.
• Use in different applications: PDCAAS was originally designed for use with infant formulas and other child-centric applications. DIAAS, on the other hand, can be used for any application where protein quality is being measured.

Whether you’re looking at casein, whey or any other protein source, protein quality should be measured on the DIAAS scale. Often a PDCAAS score will be used for protein sources of lower quality to make them look like they are higher quality. Knowing how to interpret these scores and understand what they mean is critical for consumers to know to make the most informed decisions possible about their protein intake and for food formulators to provide products that help their consumers reach their goals.

For more on both these scales for measuring protein quality, or to learn about any of our milk protein concentrate or other dairy products, speak to the team at Idaho Milk Products today.