Quality deterioration kinetics of roasted peanut matrices under fixed-time and estimated-lethality at various water activities

Water activity and particle size are critical determinants of quality stability and safety in low-moisture, lipid-rich foods. However, their combined effects during thermal processing of roasted peanut matrices remain insufficiently quantified. This study evaluated quality deterioration in roasted peanut matrices with different structural forms: crushed, flour, powder, and butter. Samples were equilibrated to water activity values of 0.11–0.92 at 25 °C and heated at 80 °C for 120 min. Colour, acid value, sensory score, and changes in relative fatty acid composition were measured. Kinetic experiments were also conducted at aw,25°C 0.32 using D-value-based thermal schedules at 85, 90, and 95 °C to relate microbial lethality to quality loss. Water activity strongly affected quality stability, with the predicted quality-favourable values varying slightly among responses. Therefore, aw,25°C (0.32) was selected as a practical condition for subsequent kinetic evaluation. Matrix performance differed between the fixed-time and D-value-based treatments. These findings describe quality deterioration under fixed-time and D-value-based thermal schedules.