Understanding starch gelatinization: The phase diagram approach

•Gelatinization and hydration of potato starch was studied with multiple methods.•Based on experimental results, a detailed phase diagram was constructed.•The gelatinization endotherm (G) is understood in analogy with eutectic melting.•The melting (M1) endotherm observed in DSC represents a liquidus line.•Swelling studies of the lamellar spacing and inter-helix distance are presented. By constructing a detailed phase diagram for the potato starch–water system based on data from optical microscopy, synchrotron X-ray scattering and differential scanning calorimetry, we show that gelatinization can be interpreted in analogy with a eutectic transition. The phase rule explains why the temperature of the gelatinization transition (G) is independent on water content. Furthermore, the melting (M1) endotherm observed in DSC represents a liquidus line; the temperature for this event increases with increasing starch concentration. Both the lamellar spacing and the inter-helix distance were observed to decrease with increasing starch content for starch concentrations between approximately 65wt% and 75wt%, while the inter-helix distance continued decreasing upon further dehydration. Understanding starch gelatinization has been a longstanding challenge. The novel approach presented here shows interpretation of this phenomenon from a phase equilibria perspective.