DETERMINATION OF SOLUBLE AND INSOLUBLE DIETARY FIBER IN PSYLLIUM-CONTAINING CEREAL PRODUCTS

A method for soluble and insoluble dietary fiber determinations was de veloped for psyllium-containing food products, which are highly viscou s in aqueous solutions. The assay is based on a modification of the AO AC soluble and insoluble dietary fiber method (991.43), which was reco mmended for nutrition labeling in the final U.S. food labeling regulat ions. We found that method 991.43 and other existing dietary fiber met hods could not be applied to psyllium food products, which exhibit hig h viscosity in aqueous solutions, because highly viscous solutions cou ld not be filtered easily. In this study, we modified AOAC method 991. 43 to accommodate the filtration process of viscous sample solutions. Sonication followed by highspeed centrifugation was used before filtra tion. The principles of the method ape similar to those for AOAC metho d 991.43, including the use of the same 3 enzymes (heat-stable alpha-a mylase, protease, and amyloglucosidase) as well as similar enzyme incu bation conditions. The modification using sonication and high-speed ce ntrifugation did not alter the method performance for analytically nor mal products such as wheat bran, oat bran, and soy fiber. Yet, the mod ification allowed the separation of soluble dietary fiber fractions fr om insoluble fractions for psyllium products with satisfactory precisi on, This method for psyllium dietary fiber determinations may be appli ed to other food products that exhibit high viscosity in aqueous solut ions.