A comparative study on radio frequency inactivation kinetics of Bacillus cereus vegetative cells and A. flavus spores in sunflower seeds: nonlinear modeling and its impact on storage stability.

Sunflower seeds are prone to contamination by foodborne pathogens, posing safety concerns. This study systematically evaluated the inactivation efficacy of radiofrequency heating treatment against Bacillus cereus vegetative cells and A. flavus spores in sunflower seeds, while investigating its impact on seed storage quality. Inactivation kinetics were compared using four models: First-order kinetics, Weibull, Log-Logistic, and Dose-response. Nonlinear models, particularly Log-Logistic and Dose-response, provided superior fits (R2 > 0.98; RMSE<0.27) for both microorganisms, accurately capturing the sigmoidal inactivation curves with "shoulder" and "tailing" behavior. Inactivation efficacy was highly dependent on process parameters; increasing moisture content (12% to 20% w.b.) and temperature significantly accelerated microbial reduction. For B. cereus vegetative cells in seeds with 12% moisture, a 6-log reduction of B. cereus vegetative cells required 12.5 min at 100 °C, whereas for A. flavus spores in seeds with 20% moisture, a 7-log reduction of A. flavus spores required 11.5 min at 80 °C. Based on kinetic analysis, optimized RF treatments (B. cereus vegetative cells: 90 °C/10 min; A. flavus spores: 80 °C/10 min) were selected for storage studies. These conditions suppressed microbial regrowth by 3-5 logs during 20-day accelerated storage and significantly retarded lipid oxidation, as evidenced by lower peroxide values and free fatty acid content compared to controls. Despite some textural softening, RF heating substantially extended microbial shelf life and maintained chemical stability. This study demonstrates that RF heating effectively inactivates target microorganisms in moisture-conditioned sunflower seeds under the tested conditions, providing kinetic data that may support the development of pasteurization processes for other oilseeds that have been moisture-adjusted prior to treatment.