Coupled ethanol-trehalose processing accelerates thawing of rapid-frozen cooked rice through water-state modulation

Freezing preserves cooked rice, but ice formation and water redistribution can cause structural and textural deterioration. The individual and combined effects of ethanol soaking and trehalose-assisted cooking on freeze-thaw behaviour, water state, texture, and microstructure were investigated. Rice was soaked in water or an aqueous ethanol solution containing 700 mL L^-1 ethanol, cooked in water or a trehalose solution (30 g L^-1), frozen at -20 or -55 °C, stored at -18 °C for 7 days, and passively thawed at 27 °C.

The ethanol-soaked/trehalose-cooked sample frozen at -55 °C (ET55) exhibited the highest freezing rate (1.37 °C min^-1) and shortest thawing time (34.3 min). Differential scanning calorimetry showed lower apparent melting enthalpy and freezable-water content in the combined-treatment samples; values for ET55 were 56.8 J g^-1 and 170.3 g kg^-1, respectively. Time-domain nuclear magnetic resonance showed shorter T_2b and T_2c relaxation times in ET samples than in the corresponding water-soaked/water-cooked controls, indicating restricted mobility of weakly bound and free water without a reduction in relative free-water signal amplitude. Scanning electron microscopy of samples frozen at -20 °C showed that the combined treatment produced a compact freeze-dried matrix with smaller pores. ET55 hardness was numerically close to that of its freshly cooked counterpart.

Coupling ethanol-trehalose processing with rapid freezing at -55 °C yielded the shortest passive thawing time. This was associated with lower freezable-water content, lower apparent melting enthalpy, and restricted water mobility. This combined approach may therefore improve thawing efficiency and freeze-thaw stability in frozen cooked rice. © 2026 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.