Collaborative Construction Of Phytosterols Nanocapsules Via Casein/pectin Complex And EGCG-assisted Antioxidation

Phytosterols is an important natural active ingredient with various important physiological functions such as cholesterol lowering,immune regulation,anti-cancer and anti-inflammatory.However,it has low solubility in water and oil,and is susceptible to oxidization during processing,storage and transportation,thus affecting its bioavailability.These deficiencies limit its application in food processing.To solve the problem,in this paper,casein and pectin were used as raw materials.Nanoencapsulation technology was used to construct phytosterols transport carrier for phytosterols protection.Furthermore,based on the interaction between gallocatechin gallate(EGCG)and casein,nanocapsules were constructed to improve the stability and antioxidant activity of phytosterols.At the same time,it also significantly improved the antioxidant properties of the nanocapsules.The encapsulation rate,loading rate,stability and bioavailability of phytosterols in nanocapsules with and without EGCG was evaluated.The mode of interaction between EGCG,phytosterols and casein was clarified.The stabilization mechanism of casein/pectin complex-EGCG-phytosterols nanocapsules was elucidated.The mass ratio between casein and pectin and the effect of different p H values on the casein-pectin complex were studied by dynamic light scattering method.The results showed that the casein-pectin nanocapsules have smaller average particle size(203 nm),polydispersity index(0.28)and a lower potential value(-32 m V)when the mass ratio was 2:1 at p H 4.0.Under these conditions,casein-pectin nanocapsules were prepared and phytosterols were embedded.When the core-to-wall ratio was 1:3,the maximum encapsulation efficiency and loading capacity were obtained,which were 91% and 21%,respectively.The effect of EGCG on the formation conditions of phytosterols nanocapsules was investigated.It was found that precipitation ocurred at the phytosterols/wall material of 1:3 and 1:4 after EGCG was added.When the ratio of phytosterols to wall material was 1:5,adding 0.4 mg/m L EGCG could increase the encapsulation efficiency and loading rate to 95% and 25%,respectively,which was significantly higher than that without adding EGCG.The structures of the prepared casein/pectin-phytosterols(NCP-PSs)nanocapsules and casein/pectin complex-EGCG-phytosterols(NCP-EGCG-PSs)nanocapsules were characterized.On the basis of fourier transform infrared spectroscopy,x-ray diffraction technique,fluorescence spectroscopy and circular dichroism,it was clarified that stable capsule shell structure was formed between casein and pectin through electrostatic interaction.Hydrogen bonds and hydrophobic interactions were formed between phytosterols and casein.Hydrogen bonding interactions were formed between EGCG and casein.The crystal form of phytosterols has been changed by encapsulation,which existed stably in the hydrophobic cavity of casein,thereby forming a stable capsule structure.During the formation of nanocapsules,the addition of phytosterols and EGCG increased the casein α-helix content by 7.43% and 14%,respectively,which facilitated the stabilization of the helical structure of casein.The results of phytosterols nanocapsules stability,antioxidant activity showed that the PDI of nanocapsules was reduced by heating for a short time,which made the system more homogeneous.Pectin improved the p H stability of phytosterols nanocapsules,while EGCG not contribute to the p H stability of nanocapsules.The nanocapsules without EGCG were stored at4°C and 25°C for 15 days.The retention rates of phytosterols were 81% and 57%,respectively.Nanocapsules supplemented with 0.4 mg/m L EGCG showed 84% and 80% retention of phytosterols after storage at 4°C and 25°C for 15 days,respectively.The presence of EGCG improved the storage stability of phytosterols.The antioxidant properties of phytosterols nanocapsules were also significantly improved.In addition,the phytosterols nanocapsules exhibited excellent controlled release properties in the gastrointestinal tract through in vitro release simulation experiments.Encapsulation of phytosterols by casein and pectin increased the bioavailability of phytosterols in NCP-PSs nanocapsules and NCP-EGCG-PSs nanocapsules by at least 43.8%.