Purdue University Graduate School

Chapter 3-6

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Microbial Inactivation and Validation of Aseptic Processing and Packaging System Using Vapor Peroxide

posted on 2024-06-23, 23:22 authored by Manoj Ram Krishna SawaleManoj Ram Krishna Sawale

Liquid hydrogen peroxide (LHP) and vapor hydrogen peroxide (VHP) efficacy as a sterilant for Bacillus atrophaeus and Geobacillus stearothermophilus spores in aseptic packaging systems under commercial sterilization conditions were evaluated in this research. The work centers on quantifying and modeling the kinetic parameters that impact peroxide sterilization efficacy, including the D and z values, that relate to the change in concentration required for a 1-log reduction in spore population and a novel Zconc parameter This comprehensive study is divided into four key investigations, each contributing critical insights to the overall understanding of peroxide sterilization processes.

The first study examined the inactivation kinetics of B. atrophaeus spores in liquid hydrogen peroxide. By evaluating different concentrations (20%, 28%, and 33%) and temperatures (up to 82.2°C), the study revealed that higher concentrations and elevated temperatures significantly enhanced spore inactivation. The Weibull model provided a more accurate fit for the data, indicating a non-linear relationship between spore reduction and exposure time.

The second part of the research explored the use of VHP for sterilizing B. atrophaeus spores. With VHP concentrations of 2500 ppm and 4450 ppm at various temperatures, the study demonstrated that higher concentrations and temperatures are highly effective for spore inactivation. Both log-linear and Weibull models accurately described the inactivation kinetics, with the Weibull model showing a slightly better fit, emphasizing the potential of VHP in achieving commercial sterility.

The third investigation focused on developing predictive models for VHP concentration and its efficacy in spore inactivation. The study evaluated VHP concentrations ranging from 2.32 mg/L to 7.35 mg/L and their impact on spore inactivation rates. The Weibull model proved particularly effective in predicting the inactivation of G. stearothermophilus and B. atrophaeus spores, offering a robust tool for optimizing sterilization protocols in aseptic packaging.

The fourth and final study of the research investigated the influence of surface roughness on spore survival during VHP sterilization cycles on plastic packaging materials. Artificial roughness on high-density polyethylene (HDPE) coupons was created using sandpaper with different grits. B. atrophaeus spores were applied to both roughened and smooth HDPE surfaces. The study finds that rougher surfaces provide more shelter for spores, reducing sterilization efficacy. For example, surfaces roughened with P-36 grit showed a 2.75 log reduction in spore count, whereas smoother surfaces with P-220 grit achieved a 4.42 log reduction. Contact angle measurements indicated that increased roughness led to more hydrophilic surfaces, with water contact angles decreasing from 149.7° for the pristine sample to 105.4° for the P-36 sample. Scanning electron microscopy (SEM) images confirmed that spores were more likely to reside in the valleys of rough surfaces, highlighting the importance of surface characteristics in optimizing VHP sterilization protocols.

The findings of this dissertation underscore the significant impact of hydrogen peroxide concentration, application conditions, and packaging material surface properties on the efficacy of spore inactivation during sterilization. By providing a comprehensive understanding of these factors, the research contributes to the development of optimized aseptic sterilization protocols, enhancing the reliability and safety of aseptically packaged food and pharmaceutical products. This work will ensure compliance with regulatory standards and improve food safety in commercial manufacturing, laying a solid foundation for future research and practical applications in VHP sterilization technology.


Degree Type

  • Doctor of Philosophy


  • Food Science

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Dr. Dharmendra Mishra

Additional Committee Member 2

Dr. Ferhan Ozadali

Additional Committee Member 3

Dr. Arun Bhunia

Additional Committee Member 4

Dr. Amanda Deering

Additional Committee Member 5

Dr. Vilas Pol