AACC Standard Norms and Instruments for UV/Vis Spectroscopy

This method for determining iron content in cereals and cereal-based products involves a reaction between iron and orthophenanthroline, followed by spectrophotometric measurement. 

This method determines acid-soluble manganese content in animal feeds by a spectrophotometric procedure.

This method determines phosphorus in yeast by modified Fiske-Subbarow colorimetric method.

This automated colorimetric method determines crude protein in feeds and feedstuffs by digesting the samples in calibrated tubes and reading the absorbance of the NH3-salicylate complex in a flow cell at 660 nm.

This method measures protein content of wheat flour or ground wheat by colorimetric determination of unbound Acid Orange 12 dye. This method is applicable to cereal grains, oilseeds, legumes, forages, animal products, dairy products, and formulated feeds or foods.

In this 5-minute biuret method, compounds with peptide linkages produce a blue-violet color with copper ions in an alkaline solution. This method is applicable to all cereal grains, such as wheat, corn, barley, rye, and oats. 

In this method, damaged starch granules are hydrated; this is followed by hydrolysis to maltosaccharides and limit dextrins by fungal alpha-amylase. Amyloglucosidase is then used to convert dextrins to glucose, which is specifically determined spectrophotometrically after glucose oxidase/peroxidase treatment.

This ultraviolet absorption method measures vitamin A in dry vitamin mixes, beadlets, oils, and emulsions, at concentrations greater than 10,000 international units (IU)/g.

This method measures vitamin A in nonfat and instantized dry milks. Milk samples are saponified and extracted in hexane or hexane/ethyl ether. Vitamin A is reacted with antimony trichloride and read spectroscopically.

This method measures vitamin A in enriched flour. Vitamin A reacts with chloroform saturated with antimony trichloride (Carr-Price reagent), resulting in a transient, blue-colored compound. The intensity of color is proportional to vitamin A content. The maximum intensity is 620 nm.

This indophenol-xylene extraction method is based on the quantitative decolorization of a blue dye (2,6-dichlorophenolindophenol) by ascorbic acid, or vitamin C. The excess (unreacted) dye is extracted with xylene and measured in a spectrophotometer. In the absence of interfering materials, the amount of ascorbic acid present in the sample is proportional to the amount of dye decolorized.

This method for measuring choline involves chemically measuring it as choline reineckate. To extract samples, they are mixed with methanol and the choline is precipitated as reineckate. The precipitate is washed, dried, and then reconstituted in acetone. The resulting acetone solution is spectroscopically measured at 526 nm to determine the amount of choline present.

Niacin is determined in vitamin and mineral concentrates (used to enrich cereals) by means of a colorimetric chemical reaction. Diluted sample solutions react with buffered ammonia solution and cyanogen bromide. The intensity of the resulting yellow color is proportional to niacin content.

Niacin (either nicotinamide or nicotinic acid) is determined chemically using a colorimetric technique. A ground sample is extracted in an alkaline medium, clarified, and reacted with sulfanilic acid and cyanogen bromide to yield a yellow color.

This method determines total and residual trypsin inhibitors in soy products, including raw and toasted soybean meals and flours, soy protein concentrates and isolates, and corn-soy mixtures. Trypsin activity is indicated by an increase in absorbance at 410 nm.

This method quantifies total carotenoid content (TCC) in cereal grains and flours as lutein equivalent, the main carotenoid in wheat and corn.