FINE-TUNING A BILE-ENZYMATIC-GRAVIMETRIC TOTAL DIETARY FIBER METHOD

A recently proposed bile-enzymatic-gravimetric total dietary fiber (TD F) method was modified and the new procedure was compared with the ori ginal method, the traditional AOAC enzymatic-gravimetric determination (AOAC Official Method 985.29), and another simplified AOAC procedure by analyzing several diet composites, including National Institute of Standards and Technology 1548 total diet reference material. The origi nal and modified bile-enzymatic-gravimetric procedures also were compa red by analyzing 9 food samples from a collaborative study of the orig inal method, The modified method consistently yielded values about 10% lower than the original method but closer to reference values and to values from AOAC Offical Method 985.29, suggesting results that are mo re in line with accepted TDF standard methodology, Our modified method was used to analyze 180 fresh-frozen diet composites with TDF values ranging from 0.6 to 3.2 g/100 g wet weight, Samples were from 2 multic enter feeding studies sponsored by the National Heart, Lung and Blood Institute: DELTA(Dietary Effects on Lipoproteins and Thrombogenic Acti vity) and DASH (Dietary Approaches to Stop Hypertension), The mean rel ative standard deviation (RSD) for duplicate analyses was 1.1%. For 40 assays of a quality control diet composite over 9 months, the standar d deviation was 0.1 g/100 g wet weight (4.9% RSD), indicating the meth od's excellent precision for routine use.