Enhancement of aqueous stability of allyl isothiocyanate using nanoemulsions prepared by an emulsion inversion point method

Abstract

Allyl isothiocyanate (AITC), an organosulfur compound in cruciferous vegetables, is a natural antimicrobial and potential chemopreventive agent. However, the instability of AITC in aqueous systems restrains its applications. In this study, oil-in-water AITC nanoemulsion was prepared by the emulsion inversion point (EIP) method, aiming at improving the aqueous stability of AITC. The optimal hydrophilic–lipophilic balance (HLBop) value of surfactants containing Tween 80 and Span 80 was established at 11.0–13.0, yielding nanodroplets with diameters of 137–215nm. The mechanism of droplet formation within the HLPop region was discussed in terms of the possible structure of adsorbed surfactant layers at the oil–water interface in multiple emulsion droplets. In a 6.5-month storage test, the droplet sizes and the count rates (intensity of scattered light) of nanoemulsions decreased only slightly by 4–13% (depending on surfactant-to-oil ratio), even in highly diluted status, indicating the desirable stability of the nanoemulsions. Moreover, the nanoemulsion demonstrated superior protection against AITC degradation (78% remaining after 60d at 30°C), compared with protein nanoparticles as well as non-encapsulated aqueous dispersion. This work shows for the first time that AITC can be formulated into nanoemulsions and thus obtains satisfactory aqueous solubility and chemical stability.