Jin, J.; (2011) Lipid foulant interactions during the chromatographic purification of virus-like particles from Saccharomyces cerevisiae. Doctoral thesis , UCL (University College London).

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Abstract

The objective of this study was to understand the mechanism of lipid fouling in chromatography through the investigation of a hydrophobic interaction chromatography (HIC) operation. This was motivated by the need to understand this phenomenon during the manufacture of biological products such as vaccines. The systematic approach and novel analytical techniques employed create a unique platform to study fouling of other chromatographic adsorbents and process feed materials. HIC is employed as a primary capture step in the purification of yeast derived hepatitis R surface antigen (HBsAg), where the required cell disruption and detergent liberation steps release high levels of lipid content into the feed stream. From lipid- rich and lipid-depleted feedstocks, comparative analysis was able to quantify the deterioration in HIC performance (binding capacities, purities and recoveries) under successive cycles. Furthermore, a full mass balance on host lipids identified the highly hydrophobic triacylglyceride as the main foulant. Intra-particle distribution and progression of lipid fouling and its effects on material adsorption and diffusion were then examined under confocal laser scanning microscopy (CLSM). In addition, high- resolution scanning electron microscopy (SEM) images of the fouled bead (after 40 cycles) confirmed that a thick lipid layer was building up on the outer bead surface. Based on these findings, the mechanism of fouling was thought to be the rapid accumulation of lipid foulant at the rim of the bead, which was aggravated by the possible diffusion hindrance resulting from multi layer adsorption. Finally, pretreatments to reduce this mechanism of chromatography fouling were evaluated in terms of improvement on feed quality and HIC performance. Selective adsorbent polystyrene XAD-4 demonstrated promising lipid removal capabilities with satisfactory HBsAg VLP recoveries. The improved feed into the column resulted in a three-fold increase in product capacity, whilst the overall yield remained constant over 40 cycles.

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