A method for forming an antimicrobial composition that includes mixing an antimicrobially active botanical oil (e.g., thymol, carvacrol, etc.) and protein within a melt blending device (e.g., extruder) is provided. Despite the problems normally associated with melt processing proteins, the present inventors have discovered that the processing conditions and components may be selectively controlled to allow for the formation of a stable, melt-processed composition that is able to exhibit good mechanical properties. For example, the extrusion temperature(s) and shear rate employed during melt blending are relatively low to help limit polypeptide dissociation, thereby minimizing the impact of aggregation and embrittlement. While the use of such low temperature/shear conditions often tend to reduce mixing efficiency, the present inventors have discovered that a carrier fluid may be employed to enhance the ability of the botanical oil to flow into the internal structure of the protein where it can be retained in a stable manner. The composition is also typically anhydrous and generally free of solvents. In this manner, the protein will not generally disperse before use and prematurely release the botanical oil.
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