Zeaxanthin (ZX) or other medically or commercially important carotenoids can be prepared in microcrystalline form, in an oily carrier liquid, to increase their bioavailability following oral ingestion. Initial processing is carried out to prepare a "rough" or "coarse-grained" carotenoid preparation containing relatively large particles of the ZX or other carotenoid, in a suitable form such as a lyophilized stable powder. The coarse-grain preparation is dissolved in a suitable solvent such as tetrahydrofuran, and mixed with a carrier liquid comprising a digestible oil (such as a vegetable oil) and an emulsifying agent. The resulting oil-and-solvent mixture is injected, along with inert gas such as nitrogen, into a vacuum chamber, where a suitable vacuum and temperature combination is used to remove the solvent in a rapid "flash" manner which does not give the carotenoid crystals time to grow larger through accretion or aggregation. This generates a microcrystalline suspension containing very small particles of the ZX or other cartenoid, in the oily liquid carrier. This product can be further processed if desired, or it can be loaded directly into watertight capsules for oral ingestion. Tests on human volunteers have confirmed that the bioavailability of this microcrystalline form is substantially higher than prior art preparations having larger particles of the carotenoid.