Mixed interfacial stabilisation of emulsions by homogenised bacterial suspensions

Microbial proteins are increasingly explored as a novel food ingredient. Previous studies have shown that gentle homogenisation methods produce stable emulsions while keeping biomasses intact. However, these emulsions have large droplet sizes which may cause instability. Applying high-energy methods can improve their stability but the microbial biomass may rupture and release intracellular material that alters the emulsion stability. To assess this effect, we investigated the impact of high-pressure disruption on Gram-positive bacterial cells and its influence on emulsion stability. Bacterial cells were disrupted under conditions comparable to high-pressure emulsification. The resulting suspension was examined for the extent of disruption based on cell size, structure, composition and surface properties. Subsequently, the disrupted cell suspension was fractionated before preparing emulsions containing 10% oil and studying selected emulsion characteristics. High-pressure treatment deagglomerated and ruptured the cells, resulting in a soluble surface-active fraction, but only about 3% of the bacterial proteins were solubilised. Surface hydrophobicity increased but charge was reduced in the biomass after treatment. Oil-in-water emulsions prepared using either the soluble or insoluble fraction of the suspension creamed during storage, whereas the emulsion containing both fractions remained stable for up to 14 days, indicating that emulsion stability is enhanced by both fractions. We assume a combination of particle (protein aggregates) and molecular effects (solubilised proteins and surface-active components) stabilising the interface under these circumstances. This study offers an integrated approach to disrupt bacterial cells and produce stable emulsions without further purification. Insights into the stabilisation mechanisms for each system are proposed.