Phenomenological investigation of moisture profiles and stress fissures formation caused by glass transition gradients during intermittent drying of rice kernels

The mechanisms of stress-induced fissuring during intermittent and continuous drying of rough rice were investigated by focusing on moisture content gradients ( MCG s) and glass transition gradients ( GTG s). A spherical model was used to predict spatiotemporal MCG s and material state transitions within the kernel. Results demonstrated that increasing drying temperature led to higher maximum and average MCG s, with a strong linear relationship between average MCG and stress cracking index ( SCI ) (R 2 = 0.85), confirming the dominant role of moisture gradients in fissure formation. Although tempering reduced MCG s, repeated drying-tempering cycles induced cyclic GTG s and recurrent re-intensification of MCG s in subsequent stages, thereby limiting tempering effectiveness. To quantitatively describe these cyclic behaviors, four model-derived indices were introduced. Higher rubbery region volume percentage ( ARRVP ) and rubbery duration fraction percentage ( RDFP ) reflected longer residence in the rubbery state, reducing drying duration (54% and 49%, respectively) but increasing fissuring (56% and 36%, respectively). Increased number of glass transition crossings ( NGTC ) and number of moisture gradient reversals ( NMGR ) were also associated with higher SCI . Overall, maintaining identical drying and tempering temperatures within 40-50 °C and limiting tempering to no more than three stages provides an effective balance between process efficiency and kernel structural damage. • Spherical model predicts rice kernel moisture and state transitions. • Tempering reduces MCG s but could induce severe GTG s. • Higher rubbery volume shortens drying duration but increases kernel fissuring. • Uniform 40-50 °C drying-tempering with ≤3 stages optimizes quality and efficiency. • NGTC and NMG R indices link cyclic gradients to stress-induced fissure severity.