Hello, my name is Hannah Bailey, and I am a PhD student working under Dr. Hans Stein at the University of Illinois. Our lab focuses on determining energy and nutrient digestibility, and in recent years we have been conducting research to determine digestible indispensable amino acid scores, abbreviated DIAAS, for a variety of human foods. We specifically conducted this experiment to determine the digestibility of amino acids and DIAAS in a few protein isolates and concentrates used in the human food industry. Protein concentrates and isolates are used as dietary protein supplements for nutritional and functional improvements of foods. On a dry matter basis, concentrates generally have a protein content of 50 to 80% and isolates are more refined, containing greater than 90% crude protein and no carbohydrates. However, protein content does not equate to protein quality, and therefore, it is important to evaluate the overall protein quality via DIAAS using the growing pig as a model. 

Six ingredients were evaluated, brown rice protein concentrate, pea protein concentrate, rapeseed protein isolate 1 and 2, which vary in processing methods, soy protein isolate, and whey protein isolate. For this experiment, 7 ileal cannulated barrows with an initial body weight of 36.5 kg were used. The experimental design was a 7 by 7 Latin square with 7 diets using each ingredient as the sole source of protein and amino acids plus a nitrogen-free diet to determine basal endogenous losses of protein and amino acids. There were 7 periods and each period was 7 days with ileal digesta collection on days 6 and 7. DIAAS was calculated at the conclusion of the experiment for two age groups; one age group was children from 6 months to 3 years, and the second age group was persons older than 3 years.

The results for standardized ileal digestibility, or SID, of some amino acids are shown in the bar graph on the bottom of this slide. The orange bar represents brown rice protein concentrate, the gray bar is pea protein concentrate, the darker blue bar is rapeseed protein isolate 1, the light blue bar is rapeseed protein isolate 2, the navy bar is soy protein isolate, and the red bar is whey protein isolate. These colors also match the bar graph on the right showing the DIAAS results with the ingredient names on the horizontal axis. For SID of amino acids, I chose to depict the amino acids that were limiting in each ingredient. Brown rice, which is a cereal grain that is limiting in lysine, had the least SID of lysine and methionine. Pea protein, a plant protein that is limiting in sulfur amino acids (methionine and cysteine) and sufficient in lysine, had among the least SID of cysteine and greatest SID of lysine. Rapeseed protein 2 which was further processed (however the processing method is proprietary information) had greater SID of all amino acids compared with rapeseed protein 1. Whey protein, a dairy protein that is limiting in histidine, had SID of all amino acids that were among the greatest of all proteins with no difference in the SID of methionine and cysteine compared with rapeseed protein 2, and soy protein had SID of histidine, lysine, and cysteine that was not different from rapeseed protein 2.

For DIAAS shown in the bar graph on the right, the DIAAS calculated for children 6 months to 3 years is depicted by the solid bar and the DIAAS for persons older than 3 years is depicted by the striped bar for each ingredient, with the first limiting amino acid for each ingredient, which determines the DIAAS value, in parenthesis on the horizontal axis. The two protein concentrates, brown rice and pea protein, had the least DIAAS for both age groups with the first limiting amino acid being lysine and sulfur amino acids, respectively, when compared to the amino acid requirements for both age groups. Whey protein, which is first limiting in histidine for both age groups, and rapeseed protein isolate 2, which is first limiting in lysine for both age groups, had DIAAS greater than 100 for persons older than 3 years making them excellent quality proteins for that age group. Soy protein was first limiting in Sulfur amino acids when compared to the amino acid requirements for both age groups, and rapeseed protein 1 was first limiting in leucine for both age groups. These two proteins had DIAAS greater than 75 for both age groups, meaning they can be considered good quality proteins.

In conclusion, whey protein isolate is an excellent quality dairy protein with a DIAAS greater than 100 for persons older than 3 years. Rapeseed protein isolate 2 is an excellent quality plant protein with DIAAS greater than 100 for both age groups, illustrating that further processing of a plant protein may be beneficial for its protein quality. Rapeseed protein isolate 1 and soy protein isolate are good quality plant proteins with a DIAAS greater than 75 for both age groups. And brown rice and pea protein concentrates are lower quality proteins that may need to be supplemented by higher quality plant or animal proteins.