University of Illinois Extension

Definition of Terms and Methods of Analyses



Two ambitious and coordinated research programs have produced recently a significant set of data on the composition, digestibility and measures of processing of dehulled soybean meal. These programs were:

  • The Soy/Swine Nutrition Research Program funded by the Illinois Soybean Program Operating Board, coordinated by the University of Illinois and involving scientists from several universities.
  • The program entitled "Opportunities for Animal Feeding with Soy", funded by the Illinois Council for Food Animal Research (C-FAR) Sentinel program and conducted by the University of Illinois.

The following tables summarize the results. These data are provided as a service to practicing nutritionists for use as an update, an expansion, and an adjunct to previously existing tables of nutrient content and digestibility.

Data are presented on an as-fed basis and on a dry matter basis as means, supported by the number of samples tested and several measures of variation. Mean values presented by the NRC publication on Nutrient Requirements of Swine, 10th Edition (1998) are provided for comparison.


The experiments were structured to provide information on both mean values and variation. Sampling was restricted to dehulled soybean meals produced by solvent extraction in the United States. In individual experiments, the samples included, among others:

  • A comparison of nine plants;
  • Samples from four different days from specific plants in Illinois, Kansas and North Carolina;
  • Samples from the seven soybean maturity zones in the U.S.


  • Total amino acids of soybean meal
  • Standardized digestible amino acids
  • Percent standardized digestibility of amino acids
  • Apparent digestible amino acids
  • Percent apparent digestibility of amino acids
  • General composition of soybean meal
  • Carbohydrate composition of soybean meal
  • Mineral composition of soybean meal

Each of these tables is presented for the USA, for each maturity zone within the USA and for Argentina, Brazil, China and India.

Definition of Terms and Methods of Analyses

Dry matter

The dry matter (DM) of a feed contains all the nutrients except water. It is indirectly determined from the moisture content of the feed. After determining the moisture content by drying the sample at 100°C for 24 hours, dry matter is calculated to be the difference (AOAC, 1995).


The ash content is determined by ignition of a known weight of the food at 600°C until all carbon has been removed. The residue is the ash and is taken to represent the inorganic constituents of the food (AOAC, 1995).

Organic matter

Organic matter is determined indirectly, by difference from the ash content (AOAC, 1995).

Protein and Amino Acids
Crude protein

Crude Protein (CP) is based on a laboratory nitrogen analysis (the Kjeldahl method), from which the total protein content in a feedstuff can be calculated by multiplying the nitrogen figure by 100/16 or 6.25. This is from the assumption that nitrogen is derived from protein containing 16 % nitrogen (AOAC, 1984). However, some portion of the N in most feeds is found as non-protein nitrogen (NPN) and, therefore, the value calculated by multiplying N x 6.25 is referred to as crude rather than true protein. Protein is made up of amino acids.

Amino acids

Amino acids are the building blocks of proteins. They are small molecules containing an amino group, a carboxylic acid group, and a side chain which determines the chemical properties. Amino acids are most commonly known as the building blocks of proteins.

Amino acids were analyzed using the Beckman 6300 amino acid analyzer (Beckman Coulter, Inc. Fullerton, CA) by the methods outlined in Spitz (1973) and Moore (1963).

Essential amino acids

The essential amino acids are those amino acids which cannot be synthesized by the body and must be supplied in feed. The essential amino acids are: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Arginine and Valine.

Nonessential amino acids

Nonessential amino acids are amino acids that can be produced by the body. The nonessential amino acids are: Alanine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Proline, Serine, and Tyrosine.

Ether extract (Crude fat)

Crude fat content is estimated by extracting a ground feed sample with diethyl ether ( AOAC, 1984). The ether soluble components (ether extract) may include true fats and oils, fatty acid esters, compound lipids and fat-soluble vitamins or provitamins such as the carotenoids, all of which may have nutritional value. However, ether extract may also contain significant concentrations of indigestible waxes, resins and essential oils. Crude fat i s a typical expression of oil content in soybean and soybean meal in the soybean processing industry.

Total lipids (Acid hydrolyzed fat)

Lipids are usually defined as those components that are soluble in organic solvents (such as ether, hexane or chloroform), but are insoluble in water. This group of substances includes triacylglycercols, diacylglycercols, monoacylglycercols, free fatty acids, phospholipids, sterols, caretonoids and vitamins A and D. This is determined via the acid hydrolyzed fat method described by (Budde, 1952). Acid hydrolysis is commonly used to release bound lipids into easily extractable forms, e.g. a sample is digested by heating it for 1 hour in the presence of 3N HCl acid.

Total dietary fiber (TDF)

Total dietary fiber is defined as the polysaccharides and lignin resistant to mammalian digestive enzymes and thus relevant to most monogastric animals with hind gut fermentation Prosky (1984).

Crude fiber (CF)

Crude fiber was analyzed using the method outlined in AOAC (1984). Crude fiber contains cellulose, lignin and hemicelluloses, but not necessarily all of these are present in the food. Crude fiber levels are gauaranteed on feed labels but TDF is a more useful measure of dietary fiber content.

Total nonstructural carbohydrates

Nonstructural carbohydrates are those that can be accumulated and then readily mobilized in order to be metabolized or translocated to other plant parts. This method quantitatively determines the amount of the total glucose following enzymatic hydrolysis with hydrolysis. Total non-structural carbohydrates (TNC) is the sum of total glucose, free fructose and free sucrose. Total non-structural carbohydrates were analyzed by the method of Smith, (1969).

Monosaccharides (Galactose, Glucose, Fructose)

Simple sugars are comprised of single sugar molecules with glucose and fructose being the most common in plants. Monosaccharrides were analyzed by the method described by Smiricky et al. (2002) with some modification. The modification was that the eluent used was water with post-column addition 300 mmol NaOH.

Oligosaccharides (Sucrose, Raffinose, Stachyose, Verbascose)

Oligosaccharides are short chains of sugars, from 2 to 20 sugar residues in length, with sucrose, a disaccharide, most prevalent. Oligosaccharides were analysed by the method described by Smiricky et al. (2002).

Uronic acids

Uronic acids are carbohydrates and are sources of energy. They are monocarboxylic acids derived by oxidation to a carboxy group of the terminal –CH 2OH of aldoses e.g. D-glucoronic acid. Uronic acids were analysed by the method described by Blumenkrantz and Asboe- Hansen (1973).

Measures of Processing
Urease Activity

Urease activity is a test used to evaluate SBM for under processing. The urease levels are used as indicators of the possible presence of toxic factors such as trypsin inhibitors. This test although useful, has met with some criticism as a measure of processing for SBM. First, low levels of urease are not always correlated with impaired animal performance. Second, urease activity of zero is not always indicative of a heat-damaged ingredient, so the assay is of no value in determining the relative severity of over processing (Araba and Dale, 1998). Therefore, the urease activity test is useful in determining whether the SBM has been heated enough to reduce the anti-nutritional inhibitors, but is not a very useful indicator in determining whether SBM has been over processed. A low urease index value of 0.05 – 0.20 has generally been considered satisfactory and an indicator of a good quality SBM. Urease levels below 0.05 mean that SBM may be over processed. Urease activity was determined using the method described in AOAC (1995).

Protein solubility in potassium hydroxide (KOH).

Protein solubility in potassium hydroxide is used as a measure of the protein digestibility of SBM. This test is used to evaluate SBM processing and this method is now preferred over the urease activity test (Araba and Dale, 1988). The test is a good indicator of over processing of SBM but not a sensitive index for monitoring under processing of SBM. A KOH solubility index that is not below 70-75 % range has been accepted as a good indicator of a good quality SBM. Protein solubility in potassium hydroxide (KOH) was determined using the method described by Araba and Dale (1988).

Protein dispersibility index

Protein dispersibility index is used as a measure of the degree of processing of SBM (Dudley-Cash, 1999). It is a measure of protein solubility in water. In PDI analysis, the water-soybean meal mixture is stirred in a mechanical blender at 8,500 RPM for 10 minutes as described by Dudley – Cash (1999).


Selected major and micro minerals were analyzed by the method outlined by AOAC (1995) using the inductively coupled plasma (ICP) spectroscope (model 137, Applied Research Laboratories, Valencia (1995). The minerals analyzed are listed below:

  • Calcium
  • Phosphorus
  • Magnesium
  • Potassium
  • Sodium
  • Sulfur
  • Chlorine
  • Copper
  • Zinc
  • Iron
  • Manganese
  • Selenium


  • AOAC — Association of Official Analytical Chemists
  • AOCS — American Oil Chemists Society
  • CP — crude protein
  • CV — coefficient of variation
  • DM — dry matter
  • ICP — inductively coupled plasma
  • KOH — potassium hydroxide
  • Max — maximum
  • Mean — Average
  • Min — minimum
  • NPN — non protein nitrogen
  • NRC — National Research Council
  • OM — organic matter
  • PDI — protein dispersibility index
  • ppm — parts per million
  • RPM — revolutions per minute
  • SBM — soybean meal
  • SE — standard error
  • TAA — total amino acids
  • TDF — total dietary fiber
  • TEAA — total essential amino acids
  • TNC — total nonstructural carbohydrates
  • TNEAA — total nonessential amino acids
  • UA — urease activity


  1. AOAC. 1984. Official Methods of Analysis. 11th ed. Association of Official Analytical Chemists, Washington, DC.
  2. AOAC. 1995. Official Methods of Analysis. 15th ed. Association of Official Analytical Chemists, Washington, DC.
  3. AOCS. 1985. Official Methods. Protein Dispersibility Index (PDI). Ba 10-65, American Oil Chemists Society, Champaign, IL.
  4. Araba, M., and N. M. Dale. 1990. Evaluation of protein solubility as an indicator of overprocessing soybean meal. Poult. Sci. 69:76-83.
  5. Blumenkrantz, N., and G. Asboe-Hansen. 1973. New method for quantitative determination of uronic acids. Anal. Biochem. 54:484-489.
  6. Budde, E.F. 1952. The determination of fat in baked biscuit type dog foods. J. Assoc. Off. Agric. Chem. 35:799-805.
  7. Dudley-Cash, W.A. 1999. Methods for determining quality of soybean meal protein important. Feedstuffs. 71(1):10-11.
  8. Moore , S. 1963. On the determination of cystine as cysteic acid. J. Biol. Chem . 238: 235-237.
  9. Prosky, L., N. J.Asp, I. Furda, J. W. DeVries, T. F. Schweizer, and B. F. Harland. 1984. Determination of total dietary fiber in foods and food products: Collaborative study. J. Assoc. Off. Anal. Chem. 67:1044-1052.
  10. Smiricky, M. R., C. M. Grieshop, D. M. Albin, J. E. Wubben, V. M. Gabert, and G. C. Jr. Fahey. 2002. The influence of soy oligosaccharides on apparent and true ileal amino acid digestibility and fecal consistency in growing pigs. J. Anim. Sci. 80 (9) 2433-2441.
  11. Smith, D. 1969. Removing and Analyzing Total Nonstructural Carbohydrates from Plant Tissue. Wisconsin Agric. Exp. Sta. Res. Report 41.
  12. Spitz, H.D. 1973. A new approach for sample preparation of protein hydrolysates for amino acid analysis. Anal. Biochem. 56:66-73.
  13. Van Soest, P.J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3584-3597.