An emulsion comprising water and an immiscible predominantly hydrocarbon-based liquid, wherein the emulsion further comprises at least one protein for inhibiting the growth of microorganisms, said protein containing or being capable of binding to one of: a monosaccharide and an oligosaccharide. Uses of the invention include, but are not limited to: applications in oil well/fracking operations where it is necessary or desirable to neutralise bacteria in the extracted liquid; as an additive emulsion for bio-diesel to reduce emissions, such as NOx etc.; and as an additive in the water of heating/cooling systems for its biocidal properties.