Formulation, characterization and antimicrobial activity of tablets of essential oil prepared by compression of spray-dried powder

Oregano essential oil (EO) was encapsulated by spray drying emulsions stabilized with polysaccharides. Both, emulsions and spray-dried powder (SDP) were characterized physicochemically and SDP was compressed into tablets with low (10% w/w) and high (20% w/w) EO content. Compression behavior, redispersibility and release of EO were studied. Antimicrobial activity of reconstituted emulsions was evaluated by disc diffusion and broth dilution. SDP showed good EO encapsulation efficiency and retained high carvacrol content. SDP with low EO content formed strong tablets, whereas SDP with high EO formed weaker tablets but with acceptable mechanical strength and friability. Oil leakage due to compression was negligible. Reconstitution of original emulsion was faster from the SDP than the tablets and the use of disintegrants did not show improvement. Interestingly, addition of croscarmellose sodium (CCS) greatly increased the release rate of EO from tablets despite lack of effect on redispersibility, possibly due to fast liquid uptake/swelling by the CCS fibres combined with repulsion between negatively charged carboxyl groups on CCS and gum Arabic resulting in opening of the microencapsulating wall. Sodium starch glycolate had small effect on release. The antimicrobial activity of reconstituted emulsions relative to neomycin ranked in the order: E. coli < Klebsiella sp < S aureus < P mirabilis.