Cabadaj, Miroslav; (2025) Isothermal microcalorimetry as a novel microbiological tool for industrial production process control: A case study of a commercial probiotic. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Safety and quality assurance testing must be an integral part of any industrial fermentation production process. It is challenging to find a method that is fast, reliable and simple to perform and which can deal with samples containing very high initial bacterial loads and that can be incorporated easily into an in-house testing procedure. Isothermal microcalorimetry (IMC) can possibly fulfil all the above. The work reported in this thesis investigated the suitability and applicability of IMC in realworld problem-solving. An industrially produced commercial probiotic was taken for a model study. The approach taken was two-phased: pragmatic and theoretical. The pragmatic phase consisted of a proof of concept that IMC has the capacity to determine, consistently and with a high degree of reproducibility, that the fermentations resulted in a good product, as precisely or better than traditional microbiological plating methods. Samples taken directly from the real fermentation process were tested using IMC and resulted in much faster turnaround testing times; higher reproducibility of the experiments; and better sensitivity in observing good versus contaminated samples. The theoretical phase consisted of developing simple equations describing exponential bacterial growth and deriving quantitative parameters such as growth rate, intercept and area under curve. The two phases complemented each other resulting in the practical application of the developed theory. This was done by studying L. rhamnosus in a controlled growth medium (MRS broth) and establishing standard references (these did not exist previously). The IMC test designed was to rapidly get permission from the management of the company to bottle the finished product and save as much time as possible from the end of the fermentation to bottling and sale with a demonstrated better accuracy that the traditional microbiological plating methods (these methods required up to two weeks of testing time). IMC was shown to be a fast (10-15 hours) and accurate method (± 3%) to get accept/reject result for the selected microbiological system with potential to be employed in other similar processes.

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