Quick Amino Acid Determination for Wheat

From the Apr 26, 2000 Issue of Bacon Bits

Wheat analysis project
Two years ago we obtained over seven hundred samples of wheat from the Soils and Nutrition Lab sample storage. These samples were identified by NIRS to be spectrally (and chemically) different from one another. Out of these, the NIRS computer program selected 100 representative samples which were analyzed for moisture, protein and 18 amino acids which included all the essential ones. The data provided up-to-date information on protein and amino acid contents of wheat presently grown in Alberta.

We found that wheat protein varied between 8 and 22 per cent with similar variations in amino acids. When the amino acids were expressed as a per percentage of protein, the coefficient of variation (SD/mean x 100) ranged from 6.3 to 13.6 per cent. Lysine had the highest coefficient of variation at 13.6 which tells us that the precision with which lysine can be predicted is lower than the other amino acids. This fact was also demonstrated by lysine having the lowest R2 (regression coefficient) of all amino acids in the regression equations. Unfortunately, this level of accuracy in predicting lysine content of wheat is only about as good as previous work by other researchers.

The amino acid analysis data were used in the calibration of the NIR System 6500 to analyze wheat for amino acids. In less time than it takes to drink a cup of coffee this machine can analyze whole wheat for moisture, protein and the following amino acids: alanine, arginine, aspartic acid, cystine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tyrosine and valine.

Practical amino acid determination
Until private labs can offer NIR analysis we still need to determine amino acid values for diet formulation purposes. These can be calculated using linear regression equations if you know the dry matter protein content of the wheat. (In the lab, protein was calculated as N x 5.7). Here is a table with the equations. The R2 values indicate the extent to which protein accounts for the amino acid in question.

Linear regression equations for calculating amino acids in wheat.

Amino acid	Intercept	Slope	R2
Alanine	0.1006	0.0276	0.79
Arginine	0.0658	0.0405	0.86
Aspartic acid	0.0771	0.0441	0.76
Cystine	0.1241	0.0183	0.63
Glutamic acid	-0.1766	0.3046	0.92
Glycine	0.1247	0.0333	0.85
Histidine	0.0533	0.0198	0.86
Isoleucine	0.0555	0.0319	0.90
Leucine	0.1489	0.0561	0.90
Lysine	0.0991	0.0203	0.64
Methionine	0.038	0.0129	0.80
Phenylalanine	0.0123	0.0464	0.92
Proline	-0.0082	0.1034	0.89
Serine	0.0886	0.0409	0.87
Threonine	0.0842	0.0238	0.78
Tryptophan	0.1012	0.0097	0.85
Tyrosine	-0.068	0.024	0.89
Valine	0.1237	0.035	0.86

Example calculation for lysine
Here is an example how to use the equations in the table for a wheat sample that was analyzed and found to contain 10 per cent moisture and 13.6 per cent protein

determine dry matter content of the sample:
100 - 10 = 90 %.
convert the protein to dry matter basis as follows:
100/90 x 13.6 = 15.11 %.
apply the equation for lysine:
0.0991 + 0.0203 x 15.11 = 0.406 %
convert lysine back to sample basis:
90/100 x .406 = 0.365 %.

Being able to calculate lysine, methionine, threonine and tryptophan accurately for wheat can improve the accuracy of diet formulation and save you money.

Sam Jaikaran, M.Sc. The contents of this page are no longer available.

For more information about the content of this document, contact Cathy Bryant.
This information published to the web on April 26, 2000.
Last Reviewed/Revised on September 25, 2006.