Supercritical carbon dioxide and enzymatic sensor technologies: advancements in food and healthcare solutions

Ensuring the safety and quality of food and biomedical products is critical to public health. However, traditional microbial inactivation methods, while effective, often degrade product quality or are unsuitable for sensitive materials such as fresh food products or temperature-sensitive biomedical items. This research presents a novel low-temperature CO2-based inactivation method for pre-packed solid food products, addressing the limitations of conventional High-Pressure Carbon Dioxide (HPCD) processes. The method was systematically investigated with key variables including temperature, pressure, microbial strains, matrix type, and gas-to-product ratios, with particular attention to microbial inactivation performance. The research, after the construction of small-scale plants for the application of the process, applied it to various natural matrices, including fresh-cut squash, melon, and almonds. Results demonstrated an extension of the shelf life by inactivating natural and contaminating microbial strains and enzymes, while maintaining product quality, especially in terms of bioactive compounds, antioxidant activity, and sensory acceptance. However, the process showed matrix dependency indicating the need for process optimisation based on product-specific characteristics. In addition to food applications, the potential of high-pressure CO2 for biomedical sterilisation was evaluated, focusing on the inactivation of SARS-CoV-2. The process, combined with minimal amounts of hydrogen peroxide, successfully inactivated the virus, making it a promising alternative for low-temperature sterilisation of sensitive materials, such as medical devices, that cannot withstand high-temperature treatments. Beyond decontamination processes, the Thesis also delves into the development of a low-cost, disposable paper-based sensor for monitoring analytes in food and biomedical applications. The sensor, based on a conductive polymer and a bi-enzymatic system, was firstly tested for glucose detection, a crucial analyte for both food quality monitoring and medical diagnostics. The sensor exhibited high selectivity, detecting glucose concentrations ranging from 100 μM to 10 mM, making it viable for use in monitoring glucose in human saliva and in food matrices. Moreover, its potential for adaptability to other analytes through enzyme modification positions it as a versatile tool for real-time product quality monitoring. The outcomes of this research contribute to the advancement of both food safety technologies and biomedical sterilisation processes. Future research directions will focus on optimising the CO2-based process for a wider range of products and scaling it for industrial applications. Furthermore, ongoing studies are evaluating the environmental and economic impacts of this technology, which will be critical for its commercial adoption. Process improvements, such as combining the process with antimicrobial agents or novel packaging solutions, are under investigation to enhance microbial inactivation and extend the applicability of the process to different food matrices. The paper-based enzymatic sensor also presents significant opportunities for further development, particularly in expanding its applications to other bioanalytes, improve sensor stability and sensitivity by the integration of nanotechnology and enzyme immobilisation techniques, or the potential integration of these sensors with Internet of Things (IoT) technologies. In conclusion, the work presented in this Thesis introduces novel technologies for the food and biomedical industries, with the potential to improve microbial inactivation processes and real-time quality monitoring. Further research and optimisation will be critical in scaling these technologies for widespread commercial use, with promising implications for food safety, biomedical sterilisation, and environmental sustainability.