Sorption isotherm and state diagram for indica rice starch with and without soluble dietary fiber

Moisture sorption isotherms and state diagrams for indica rice starch (IRS) and indica rice starch-soluble dietary fiber (IRS-SDF) were developed to investigate the effect of SDF on the stability of IRS. Sorption isotherms of IRS and IRS-SDF were determined by the static gravimetric method and the data were modeled by Guggenheim-Anderson-de Boer (GAB) model. The GAB monolayer moisture contents were calculated to be 7.43 and 8.37 g/100g (dry basis) for IRS and IRS-SDF, respectively. The state diagram was composed of the glass transition line and freezing curve, which were fitted according to Gordon-Taylor and Chen models, respectively. The ultimate maximum-freeze-concentration conditions were calculated as characteristic glass transition temperature (Tg') of −42.5 °C and −31.5 °C with characteristic solids content (Xs') being 0.71 and 0.72 g/g (wet basis), and characteristic temperature of end point of freezing (Tm') being −18.2 °C and −13.8 °C for IRS and IRS-SDF, respectively. The state diagrams and sorption isotherms of IRS and IRS-SDF have great significance for evaluating storage stability, optimizing drying and freezing processes.