Functional and Anthocyanin Stabilization of Rice Coproduct Powder: Linking Freeze-Drying Structure, Glass Transition, and GAB Monolayer for Predictive Shelf Life

Valorization of anthocyanin-rich coproducts, such as broken Homnil rice (HN), is limited by the poor kinetic stability of anthocyanins during storage, constraining their use in value-added functional foods. This study aimed (i) to mechanistically link the structural and thermodynamic properties of maltodextrin/pectin-encapsulated HN powders to anthocyanin stability and (ii) to compare two low-temperature drying treatments, freeze-drying (HNFD) and vacuum-drying at 60 °C (HNVD), as stabilization strategies. HNFD developed a highly porous matrix and significantly higher encapsulation efficiency (88.93%, p < 0.05), together with a glass transition temperature ( T g ) of 82.05 °C, which was lower than that of HNVD (223.39 °C). The activation energy for anthocyanin degradation was similar for both treatments (31.74 kJ/mol·K for HNFD vs 32.76 kJ/mol·K for HNVD over 4 weeks), indicating comparable kinetic stability. Water sorption isotherms at 25–45 °C were best described by the Guggenheim–Anderson–de Boer model, with R 2 > 0.99, identifying the monolayer moisture content ( M 0 ) as the critical thermodynamic stability threshold and confirming that the initial water activity of HNFD ( a w = 0.1743) lies within this stable M 0 region. These findings demonstrate that freeze-drying confers a superior kinetic and thermodynamic barrier to anthocyanin degradation compared to vacuum-drying and, for the first time for this system, provide integrated T g - E a -GAB ( M 0 ) metrics that move beyond empirical shelf life descriptions to support predictive process and packaging design (e.g., choosing drying conditions, storage humidity, and barrier properties) for long-term stability of functional food powders derived from rice coproducts, enabling more robust shelf life predictions for rice coproduct powders.