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Jin Hong Mok PhD dissertation.pdf (3.18 MB)

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Nonthermal Inactivation of Bacteria in Liquids Using a Combination of Mechanical Shear and Moderate Electric Fields

Mok, Jin Hong
http://orcid.org/0000-0003-4369-0905
http://rave.ohiolink.edu/etdc/view?acc_num=osu1555609969589384

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Food, Agricultural and Biological Engineering.
We investigated a novel combination treatment involving shear stress (SS) and moderate electric field (MEF) for nonthermal pasteurization of fruit and vegetable juices. We further investigated this combination incorporating nisin (NS) for the same purpose. Our hypotheses were that the effect of mechanical shear (mechanical/physical cell disruption) could be simultaneously combined with moderate electric field (enhanced cellular permeabilization) and nisin (pore formation in cell membrane) in a synergistic manner to ensure food safety while maintaining quality in fruit and vegetable juices. Assurance of safety and longer shelf life of food products requires inactivation of food spoilage and pathogenic bacteria, since juice products are a rich source of nutrients that support microbial growth and activity. Recently, due to growing demand for health-promoting properties, the food industry has investigated a number of nonthermal techniques and their combination strategies for maintaining fresh-like characteristics as alternatives to thermal pasteurization and sterilization. The objectives of this research were to: 1) determine the disinfection effects of SS and MEF treatments individually, or in simultaneous combination (SS+MEF) on the inactivation of Gram-negative (Escherichia coli K12) and Gram-positive bacteria (Listeria innocua) inoculated onto fruit and vegetable juices, 2) determine the combined consecutive or simultaneous combination effect of SS+MEF with mild heat or NS on microbial inactivation rates and levels to find the optimized treatment conditions, 3) investigate the contribution of different mechanisms to bacteria inactivation and injury, 4) evaluate a non-linear kinetic model predicting the survival ratios and metabolic activities of both test microorganisms under applied time-varying treatment conditions, and 5) analyze and assess selected quality attributes of these processed products and compare them with those of untreated products. Findings indicated that individual SS and MEF can cause microbial reduction, with the effects increasing with treatment intensity, controlled by shear rate (for SS) and duty cycle (for MEF), and treatment time. The bactericidal effects of SS+MEF were improved when combined with mild heat, decreasing E. coli K12 counts by about 5-log reduction within 7.5 min at 50°C. Combined SS+MEF with NS consecutively and simultaneously (SS+MEF→NS and SS+MEF+NS, respectively) resulted in a 5-log reduction within 5 min at 27°C against both E. coli K12 and L. innocua with in apple and apple-kale blend juices. Interestingly, knowledge of shear history and controlling cumulative energy dissipation is critical for conducting shear stress effects on microbial inactivation studies. Mechanisms for SS+MEF→NS or SS+MEF+NS treatment on microbial inactivation were proposed as these findings open opportunities for future research endeavors against different foodborne pathogen species. The SS+MEF+NS treatment itself did not affect the selected quality attributes of juice products (pH, color, DPPH, and chlorophyll contents), compared to untreated samples. Overall, these results indicate the feasibility of SS+MEF+NS combination as an alternative nonthermal juice pasteurization technology and contribute toward understanding of how SS+MEF+NS treatment affects microbial cell physiological states.
Sudhir Sastry (Advisor)
Ahmed Yousef (Committee Member)
Dennis Heldman (Committee Member)
Gonul Kaletunc (Committee Member)
160 p.
Agricultural Engineering; Food Science
Mechanical shear; moderate electric fields; nisin; combination technology; pasteurization; fruit and vegetable juices

Recommended Citations

Citations

  • Mok, J. H. (2019). Nonthermal Inactivation of Bacteria in Liquids Using a Combination of Mechanical Shear and Moderate Electric Fields [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555609969589384

    APA Style (7th edition)

  • Mok, Jin Hong. Nonthermal Inactivation of Bacteria in Liquids Using a Combination of Mechanical Shear and Moderate Electric Fields. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1555609969589384.

    MLA Style (8th edition)

  • Mok, Jin Hong. "Nonthermal Inactivation of Bacteria in Liquids Using a Combination of Mechanical Shear and Moderate Electric Fields." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555609969589384

    Chicago Manual of Style (17th edition)

osu1555609969589384
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This open access ETD is published by The Ohio State University and OhioLINK.