In one aspect, methods of preparing composite nanoparticle compositions are described herein. For example, in some embodiments, a method comprises providing a zein solution stream, an organic fluid stream including at least one additive and at least one buffer fluid stream. The zein solution stream, organic fluid stream and buffer fluid stream are delivered to a chamber for mixing at one or more rates sufficient to flash precipitate composite nanoparticles including the additive encapsulated by a shell comprising the zein.