Water Sorption Characteristics of Dietary Fibers

The water sorption characteristics of water-soluble dietary fibers (SDFs), and water insoluble ones (IDFs) were investigated with regard to their adaptability to 10 kinds of sorption isotherm equations, and a comparison of their monolayer water contents calculated by the BET, Caurie and GAB equations. The adaptability, estimated on the basis of root mean squares (RMSs), and the correlation coefficient for linear expressions of the isotherm equations and for the quadratic GAB equation were greater for SDFs than for IDFs. By these equations, the adaptability varied among the IDFs, and the equations deduced from monolayer and/or multilayer water sorption models tended to give lower correlation coefficients and higher RMS values. Smith's equation. was the most adaptable one for all dietary fibers except wheat bran and chitin. The GAB equation also fitted well, although it was impossible to calculate the monolayer water content of IDFs. The monolayer water contents of SDFs (4-12 g) were greater than those of IDFs (<8 g/100 g of dry matter). Based on these results, the mechanism for water sorption was recognized to be different between SDF and IDF. (Received November 24, 1992)