Studying the digestibility of cereal grains

June 5, 2014

Nutrient digestibility is an important aspect of nutrition, but it can be hard to measure in humans. Researchers at the University of Illinois are using digestibility studies in pigs to improve human nutrition by determining the quality of protein in cereal grains.

In a study published in the British Journal of Nutrition, the researchers published digestible indispensable amino acid score (DIAAS) values for eight cereal grains that may be used in human nutrition: yellow dent corn, Nutridense corn, dehulled barley, dehulled oats, polished white rice, rye, sorghum, and wheat. The DIAAS is a new measurement to describe the protein content of foods that was recommended by the Food and Agriculture Organization of the United Nations (FAO) in 2013. The DIAAS takes into account the concentration and ileal digestibility of each indispensable amino acid in the protein. Ileal digestibility studies are impractical to conduct in human subjects so animal models are often used to determine amino acid digestibility. The growing pig is the animal model recommended by FAO.

The researchers determined the standardized ileal digestibility of amino acids for the eight cereal grains when fed to growing pigs. They then converted ileal digestibility values to DIAAS using a formula that compares the digestible amount of a given indispensable amino acid in one gram of the dietary protein to the digestible amount of that amino acid in one gram of the reference protein, where the reference protein is the “ideal” protein in terms of amino acid composition. The DIAAS value of the reference protein is 100.

The DIAAS values for the eight cereal grains evaluated by the researchers were: 77 for dehulled oats, 64 for polished rice, 54 for Nutridense corn, 51 for dehulled barley, 48 for yellow dent corn, 47 for rye, 43 for wheat, and 29 for sorghum.

“In most cases, the concentrations of digestible amino acids in cereal grains are not sufficient to fulfill requirements for proper growth and development,” said Hans H. Stein, Professor of Animal Science at the University of Illinois. “What we observed is that diets based on yellow dent corn, rye, and sorghum requires more amino acid supplementation than diets based on rice, dehulled oats, dehulled barley, Nutridense corn, or wheat.”

He added that cereal grains and grain co-products for human consumption are usually cooked or processed before being consumed and that further work is needed to estimate the effects of food preparation and processing on protein quality.