| Polyglycerol fatty acid esters(PGFEs),a kind of safe and efficient non-ionic surfactant,exhibit broad prospects in applying for the functional emulsion formulations due to their emulsifying and antibacterial properties.However,the current studies on PGFEs used in the emulsions have mainly focused on the effect of PGFEs compositions on the physicochemical stability of the emulsions,and few researches are available exploring systematically how PGFEs compositions,especially the aliphatic chain lengths of PGFEs,affect the functional characteristics and bioaccessibility of encapsulated bioactive substances.Hence,PGFEs with different aliphatic chain lengths(C8～C18)were synthesized enzymatically to develop curcumin-loaded nanoemulsions using as emulsifiers,and the effects of aliphatic chain lengths in PGFEs on the stability,in vitro release,functional properties and digestive characteristics of curcumin-loaded nanoemulsions were evaluated.The experimental results were shown as follows:(1)Enzymatic synthesis and characterization of PGFEs.Crude polyglycerols were purified through optimizing the molecular distillation temperature(120 ℃).PGFEs with different aliphatic chain lengths were synthesized using Novozym 435 as a catalyst,and their esterification rate(93%～98%)increased with a reduction in the chain lengths of fatty acids.Determined by fourier transform infrared spectrum,high performance liquid chromatography-evaporative light scattering and electrospray ionization-mass spectrometry,synthesized products mainly composed of monoesters(75%～85%)were indeed PGFEs,and could be applied as oil-in-water emulsifiers due to their hydrophile-lipophilic balance values above 7.(2)Effect of the aliphatic chain lengths in PGFEs on the stability and functional properties of curcumin-loaded nanoemulsions.PGFEs with C10～C18 chain lengths were able to stabilize nanoemulsions,and the formed nanoemulsions showed smaller particle sizes and higher ζ-potentials as the aliphatic chain lengths of PGFEs decreased.PGFEs-stabilized nanoemulsions displayed good storage stability at 4 ℃ and 30 ℃,while rapid growth of droplets and sharp degradation of curcumin were observed at 50 ℃.Curcumin in the nanoemulsions exhibited higher ultraviolet degradation rate and in vitro release rate when decreasing the aliphatic chain lengths of PGFEs.Nanoemulsions stabilized by PGFEs with C10～C12 chain lengths not only improved the antioxidant activity of curcumin,but also exhibited good antibacterial activity against Staphylococcus aureus and Escherichia coli.(3)Effect of the aliphatic chain lengths and concentrations in PGFEs on the digestive characteristics of curcumin-loaded nanoemulsions.PGFEs-stabilized nanoemulsions were unstable under gastric phase,and an increase in PGFEs concentrations or reduction in the aliphatic chain lengths of PGFEs could decrease the aggregation of droplets within the gastrointestinal tract.Long-chain PGFEs(C14～C18)could promote lipid hydrolysis of nanoemulsions.PGFEs with C10～C12 chain lengths significantly enhanced curcumin bioaccessibility(82%～92%),while long-chain PGFEs significantly decreased curcumin bioaccessibility(49%～75%)with an increase in their concentrations or aliphatic chain lengths.These phenomena were related to the improved solubilizing capacity of mixed micelles induced by free fatty acids(FFAs)with C10～C12 chain lengths,and the insoluble precipitation of mixed micelles and calcium ions caused by long-chain FFAs.In summary,due to their inherent antibacterial activity and the solubilization effect on curcumin,PGFEs with C10～C12 chain lengths can develop curcumin-loaded nanoemulsions which exhibit good antibacterial activity,higher antioxidant activity and curcumin bioaccessibility,providing experimental basis for PGFEs applied in functional emulsion formulations. |
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