Optimizing high hydrostatic pressure: a synergistic approach with natural antimicrobials

Giannoulis, N. (2026) Optimizing high hydrostatic pressure: a synergistic approach with natural antimicrobials. PhD thesis, University of Reading. doi: 10.48683/1926.00129941

Abstract/Summary

High Hydrostatic Pressure (HHP) is a promising non-thermal food processing technology for improving food safety and extending shelf life. However, its broader adoption is constrained by high operational costs and the increased pressure levels required to achieve safety targets. This thesis explores the potential of combining HHP with natural antimicrobials (NAs) to improve microbial inactivation under milder pressure conditions, with a particular focus on Listeria monocytogenes, a major foodborne pathogen of concern. Three natural antimicrobials (chitosan, nisin, and a blueberry-derived product) were investigated for their synergistic effect with HHP across both model systems and real food matrices. In laboratory media (BHI and ACES buffer), the combination of HHP with chitosan or nisin resulted in greater inactivation of L. monocytogenes compared to the individual treatments, with temperature, pressure intensity, and strain variability strongly influencing the extent of synergism. Broadening this approach to food matrices, HHP combined with nisin or a blueberry-derived product enhanced L. monocytogenes control in beef and plant-based burgers and contributed in the extension of shelf life during chilled storage. In oat-based milk alternatives, nisin addition significantly reduced the time to achieve a 3-log reduction compared to HHP alone, offering an effective hurdle strategy for the safe production of refrigerated, clean-label PBMAs. Further investigation across multiple PBMAs (oat, almond, soy, hazelnut, coconut) revealed matrix-dependent variability, with the HHP - nisin combination consistently demonstrating synergistic effect and providing novel insights into its applicability as a clean label strategy for L. monocytogenes control. Collectively, this work demonstrates that combining HHP with natural antimicrobials can lower pressure requirements, enhance microbial safety, extend shelf life, and broaden the applicability of HHP to rapidly growing plant-based food categories. These insights establish a scientific foundation for the industrial implementation of minimally processed, and sustainable HHP-based preservation strategies that meet consumer demand for clean-label, safe food products.

Item Type	Thesis (PhD)
URI	https://centaur.reading.ac.uk/id/eprint/129941
Identification Number/DOI	10.48683/1926.00129941
Divisions	Life Sciences > School of Chemistry, Food and Pharmacy > Department of Food and Nutritional Sciences
Date on Title Page	October 2025
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