Comparative study of mechanical cell disruption methods on bacteria and fungi

With increased demand for protein, microorganisms such as bacteria and fungi are considered potentially important protein sources. Yet, these microbial proteins are encapsulated by their cell walls, which limits their solubility and in turn restricts any possible emulsifying or foaming abilities for food applications . In this study, we aimed to improve the soluble protein recovery from a Gram-positive bacterium Clostridium tyrobutyricum and a filamentous fungus Rhizomucor pusillus and assess the quality of the soluble extracts. The suspensions were pretreated by pH adjustments followed by microfluidisation, ultrasonication or a combination of the two to permeabilise and disrupt the cells. The effectiveness of the treatments were assessed by the soluble protein recovery, particle size and microscopy while the soluble fraction was characterised based on its relative composition and size. Furthermore, the energy consumed for each treatment was computed to understand the process efficiency. pH greatly influenced the cell permeability and disruption effectiveness. Bacterial cells were more easily lysed at low pH using ultrasonication (49.6% recovery), achieving a high efficiency of 10 kJ/g protein recovered and obtaining protein-rich soluble fractions that assembled into worm-like aggregates. Conversely, the highest recovery for the filamentous fungus occurred using a combined treatment at high pH (29.1% recovery), which was less energy-efficient than ultrasonication alone (358 kJ/g protein recovered). Unlike bacteria, the soluble fungal extract contained more carbohydrates than proteins with larger hydrodynamic sizes. These findings demonstrate the influence of microbial cell structure and composition on protein extractability and its characteristics for future implementation in food applications.