AOAC 993.21 Total Dietary Fiber in Foods and Food Products

The AOAC 993.21 standard, developed by the Official Society of Analytical Chemists (AOAC), defines a non-enzymatic - gravimetric method for determining the total amount of dietary fiber in foods and food products.

According to this test method, dried fruit, vegetables, or isolated sources of fiber are suspended in water and incubated for 37 minutes at 90 degrees Celsius to dissolve sugars and other water-soluble components. The fiber components are then precipitated with ethanol and the residue is washed sequentially with 78 percent ethanol, 95 percent ethanol and acetone, and then dried at 105 degrees.

The term fiber is defined by Commission directive 90/496/EC amending Council directive 2/2008/EEC100 on nutritional labeling of foodstuffs with regard to recommended daily amounts, energy conversion factors and definitions. Accordingly, fiber refers to carbohydrate polymers with three or more monomeric units that are not digested or absorbed in the human small intestine and fall into the following categories:

• Edible carbohydrate polymers naturally found in food as consumed
• Edible carbohydrate polymers obtained from food raw materials by physical, enzymatic or chemical means and whose beneficial physiological effects are demonstrated by generally accepted scientific evidence.
• Edible synthetic carbohydrate polymers with a beneficial physiological effect demonstrated by generally accepted scientific evidence

Total dietary fiber in foods is determined by the enzymatic-gravimetric method, which is measured using phosphate buffer systems. Double portions of the sample from dried (degreased if necessary) foods are gelatinized and partially digested with alpha-amylase, then enzymatically digested with protease and amyloglucosidase to remove protein and starch present in the sample, simulating human digestion.

The residue is then filtered and washed with ethanol and acetone, then dried and weighed. Part of the sample is analyzed for protein, the other part is ashes. In tests performed in advanced laboratories, total dietary fiber is calculated by subtracting the weight of protein and ash from the weight of the residue.

Our organization also provides testing services for total dietary fiber in foods and food products, within the scope of the AOAC 993.21 standard, with its trained and expert staff and advanced technological equipment, among the numerous test, measurement, analysis and evaluation studies it provides for businesses in various sectors.