Determination of the viability and release profile of compression coated probiotic cells using fluorescent staining and flow cytometry

Aim. Previous studies have shown that compression coating improves the storage stability of freeze-dried Lactobacillus acidophilus, although this stability is related to the degree of cell injury, which in turn is related to the compression pressure used. Compression coating has also been found to improve the survival of freeze dried L. acidophilus during exposure to simulated gastric fluid (SGF). The aim of the present work is to monitor and refine the release profile of a compression coated L. acidophilus formulation, with targeted release at the terminal ileum and beginning of the colon in the human gastrointestinal tract. Methods. Dissolution studies were performed using a phosphate buffer with a pH of 2 and 6.8, to simulate gastric fluid and intestinal fluid (SIF), respectively. Cell viability was monitored using a Microcyte flow cytometer, together with traditional dilution plating (CFU/mL). Results. Results show that an enteric coating material, Eudragit L100-55, is both suitable for compression coating, and enhancing the survival of cells when exposed to SIF. Pectin USP 100 has also been shown to promote targeted release of the cells, via its swelling properties upon hydration. Conclusion. This work shows the importance of encapsulation with respect to cell physiological state including viability during exposure to SGF, and highlights the potential of flow cytometry as a rapid technique for the monitoring and optimisation of probiotic cell physiology during processing conditions.