State Diagram for a Waxy Rice Starch–Soluble Dietary Fiber Composite System

Abstract

Soluble dietary fiber (SDF) significantly affects human health. The addition of SDF to food not only improves the health benefits, but also modifies its textural properties and shelf life. Moisture sorption isotherms and state diagrams are developed for waxy rice starch (WRS) and waxy rice starch–soluble dietary fiber (WRS‐SDF) to investigate the effects of SDF on the stability of WRS. The moisture sorption isotherms of WRS and WRS‐SDF are modeled using the Guggenheim–Anderson–de Boer (GAB) equation. The GAB monolayer moisture contents are calculated as 8.87 and 9.28 g/100 g (dry basis) for WRS and WRS‐SDF, respectively. For WRS, the maximal‐freeze‐concentration conditions at Xnormals′ (characteristic solids content) = 0.75 g g−1 (dry basis) are Tnormalm′ (characteristic end point of freezing) = −16.8 °C and Tnormalg′ (characteristic glass transition) = −38.5 °C. For WRS‐SDF at Xnormals′ =0.74 g g−1 (dry basis), Tnormalm′ = −13.5 °C and Tnormalg′ = −29.6 °C. The differences in values of the maximal‐freeze‐concentration conditions are attributed to the good hygroscopicity and water‐holding capacity of SDF. When combined with the Williams–Landel–Ferry (WLF) equation, the results indicated that the storage of WRS‐SDF is shorter than that of WRS under the same holding condition.