Dietary Fiber Content of Cereal and Grain Products Determined by Enzymatic–Chemical and Enzymatic–Gravimetric Methods

Abstract

The two objectives of this research were to compare total dietary fiber values obtained by the AOAC enzymatic–gravimetric method and the Uppsala enzymatic–chemical method for 50 grain and cereal products and to compare the fiber content and composition of foods that are likely to be grouped during nutrient intake studies. Mean fiber contents of 44 refined grain products determined by the two methods were significantly different ( P < 0.01), 2.5 ± 1.2 g/100 g (fresh wt) by the AOAC method and 2.0 ± 0.7 g/100 g by the Uppsala method. Mean fiber contents of 6 higher fiber foods also were different ( P < 0.01), 9.1 ± 1.6 and 7.9 ± 1.2 g/100 g, respectively. Data from the two methods of analysis were strongly correlated, r 2 = 0.93 ( P < 0.001). The soluble fiber content of the refined products was an average of 25% of total fiber, of the higher fiber products, 20%. Ingredients influenced the fiber content and composition of the samples; some such as fat and sugar diluted the fiber concentration and others such as fruit, nuts, coconut, and chocolate increased it. We conclude that complete descriptions should be obtained if food intake records are to reflect fiber intake; grouping some foods prior to calculating fiber intake is likely to lead to errors and fiber intakes calculated from AOAC fiber data will be higher than those determined by the Uppsala fiber method. Because a more specific set of analyses would be likely to provide more accurate results, we recommend that data obtained using an enzymatic–chemical method be used to calculate fiber intake in nutritional studies.