Modifications of the AOAC Total Dietary Fiber Method

Abstract

Dietary fiber is generally defined as plant components that are indigestible by the human digestive enzyme system (1). Thus, total dietary fiber (TDF) includes nonstarch polysaccharides, lignin, and associated substances (1). Determination of the TDF requires an analytical method which measures all of the above components of TDF, The method should be simple, reliable, fast, and inexpensive enough to be performed on a routine basis, with large numbers of samples. The Association of Official Analytical Chemists (AOAC) employed a three-step enzymatic digestion for removal of starch and protein (2, 3). The AOAC method is simple and easy to run. Total dietary fiber is precipitated with 4 volumes of 95% ethanol, filtered and dried. Residues are then corrected for protein and ash to derive TDF values. The reported assay variability is relatively high (2, 3). In this study, we modified the AOAC method in an attempt to improve the precision of the assay.