Soy Protein As A Nanocarrier For Curcumin And The Possible Mechanisms Involved

Keeping stability and bioavailability of bioactive ingredients is important in functional foods preparations.Due to its potential of enhancing solubility,stability and bioavailability of bioactive ingredients effectively,protein-based nanocomplexes have been getting more and more interesting.Otherwise,plant proteins have been improved to be health for human beings.However,the studies of plant proteins-based nanocomplexes were not as much as that of animal proteins-based nanocomplexes yet.This study systematically investigated the preparation,characterization and application of soy protein nanocomplexes as effective curcumin carriers.The main conclusions are as follows:1.The nanocomplexation between soy proteins and curcumin was studied to reveal whether soy proteins could form nanocomplexes with bioactive ingredients and what the key factors are.Curcumin bound to the hydrophobic clusters of soy proteins to form stable soy proteins-curcumin nanocomplexes.According to the dynamic light scattering technique and atomic force microscopy results,it was found that the morphology and z-average diameter of the nanocomplexes were spherical and less than 100 nm respectively.After complexation,the water solubility of curcumin was enhanced above 98000 folds(compared to that of free curcumin in water),and the stability and bioaccessibility of curcumin were also significantly improved.The ultrasonic pretreatment soy protein had higher encapsulation potentials than the native ones,and formed the nanocomplexes with higher loading amount of curcumin(14.45%vs.10.39%).The numbers and natures of hydrophobic clusters are the key factors for soy protein nanocomplexation with curcumin,while either the hydrophobic interactions or disulfide bonds is indispensible to maintain the structure of hydrophobic sites suitable in soy protein for curcumin binding.2.The synergistic effects of soy polysaccharide coating on transporation properties of soy protein-based nanocomplexes were studied,and the core-shell complex nanoparticles as carriers for curcumin were prepared through the electrostatic interactions between soy protein and soy polysaccharide.The core-shell structure formed at pH 7.0 might be loose,while the ones formed at pH 4.0 might be more compact and ordered.The complex nanoparticles improved the stability and sustained release of curcumin more than that of soy protein-curcumin nanocomplexes,and were well dispersible and colloidal stable in water.3.The preparation of soy protein-curcumin nanocomplexes powders by spray drying was studied.The curcumin retention of the curcumin loaded nanocomplexes powder prepared with soy protein/soy polysaccharide or/and maltodextrin mixed wall material were better than that with soy protein single wall material(92~98%vs.89%),as well as the capacity of solubility and dispersibility.Polysaccharides adding were necessary to inhibit aggregation of soy protein during storage at the room temperature and high humidity conditions,and the z-average diameter of particles in the dried/reconstituted soy polysaccharide/maltodextrin-soy protein-curcumin nanocomplexes were less than that in the soy protein-curcumin nanocomplexes(0.179μM vs.3.6μM).4.The effects of nanocomplexation on antioxidant and anticancer properties of curcumin were evaluated.After nanocomplexation with soy protein,the ORCA value and DPPH~-radical scavenging activity of curcumin was higher than that of free curcumin,while the inhibition of cellular proliferation of HepG2 was also enhanced,suggesting the antioxidant and anticancer bioactivities of curcumin were improved by complexation with soy protein.Furthermore,the inhibition of cellular proliferation of bioaccessible curcumin after in vitro simulated gastrointestinal digestion of free curcumin and protein-bound curcumin was also evaluated,and the results showed that the more curcumin transferred to the bile salts micelle,the higher anticancer activity was,indicating that the bioavailability of curcumin is positive correlation with its anticancer activity.In a word,soy protein-based nanocomplexes are effective nanocarriers to enhance solubility,stability and bioavailability of curcumin,which may be applied in functional foods formulations.