Study On Structural Characterization,Emulsion Preparation And Application Of Mango Kernel Shell Cellulose Nanofibers

Emulsions that use solid particles instead of traditional surfactants as stabilizers are known as Pickering emulsion,which are widely used in food,pharmaceutical and cosmetic applications because of their simple system and high physical stability.Cellulose is an excellent source of solid particles for Pickering emulsions due to its wide range of sources,good biocompatibility and ease of modification.Mango kernels are processing by-products of mangoes,and their utilization rate is much low.Mango kernel shells are a good source of cellulose extraction because they account for about30% to 35% of mango kernels,of which the cellulose content is about 39%.In this work,mango kernel shell cellulose nanofibers(MKSCNFs)were prepared by TEMPO oxidation and high-pressure homogenization method,their structural properties were characterized and analyzed,and their performance in stabilizing Pickering emulsion was investigated.Then the hydrophobicity was modified by using whey isolate protein to prepare whey isolate-mango kernel shell cellulose nanofibers(WPI-MKSCNFs)composite particles,and their storage stability and environmental stability changes in the preparation of Pickering emulsions were comprehensively evaluated.Finally,the stability and in vitro digestibility of the WPI-MKSCNFs Pickering emulsions loading curcumin were investigated.The main results were as follows:(1)Filamentous MKSCNFs were prepared from mango kernel shells by TEMPO oxidation combined with high-pressure homogenization and their structural properties were characterized and analyzed,and the effects of p H(5-11)and ionic strength(10-100 mmol/L)on their performance in stabilizing Pickering emulsions were investigated.The results showed that MKSCNFs carry a negative charge on the surface and the cellulose crystalline type was Ⅰ cellulose,which retained the basic structure of cellulose,the crystallinity reduced to 57% and the thermal stability was reduced,but still maintained a high thermal stability performance.The average particle size of MKSCNFs Pickering emulsion decreased with increasing p H and had the smallest particle size of about 469.5 nm at p H 11,with a more uniform particle size distribution.The 30-day creaming index(CI)was 58.8%,showing good storage stability.The ionic strength had great effect on Pickering emulsions stabilized by MKSCNFs,emulsions were more prone to rapid delamination during storage when the ionic strength was greater than 50 mmol/L.Therefore,it was found that MKSCNFs have the potential to be used as solid particles in Pickering emulsions,but their stability needs to be further improved.(2)Hydrophobic modification of MKSCNFs using WPI was conducted and changes in the storage stability and environmental stability of Pickering emulsions after their modification was investigated.The results showed that WPI-MKSCNFs complexes with strong electrostatic interactions,high free energy for interfacial desorption and excellent emulsification properties could be formed at p H 3,WPI/MKSCNFs = 1:1.Then the physicochemical properties of the emulsions were determined at different concentrations(0.25-1.25 wt%),ionic strengths(25-200mmol/L)and temperatures(4-55 °C).The results demonstrated that when the concentration of WPI-MKSCNFs complex was 1.25 wt%,the emulsion showed excellent stability performance,and the average particle size of the emulsion increased from 6.67 μm to 10.94 μm after 30 d of storage,but still maintained a good particle size distribution without obvious aggregation,and the CI was 0.Compared to the unmodified MKSCNFs,the WPI-MKSCNFs complex was less sensitive to ionic strength.At an ionic strength of 25 mmol/L,the emulsion had the smallest mean particle size of 7.46 μm after 30 d and the best storage effect with a CI of 0.The changes of temperature had little influence on WPI-MKSCNFs emulsions.When the temperature was at 37 ℃ and 55 ℃,the emulsions appeared slight stratification after 30 d of storage,and the CI was 1.72% and 5.44% respectively.These results indicated that the addition of WPI significantly improved the emulsification performance of MKSCNFs.(3)The WPI-MKSCNFs Pickering emulsion system loaded with curcumin was used to study its stability performance and in vitro digestive properties.The results showed that the storage stability of the emulsions and the retention of curcumin increased with increasing concentrations of WPI-MKSCNFs complexes(0.50-1.25wt%).The mean particle size of the emulsions after 30 d storage was 10.19 μm(0.5wt%),9.40 μm(0.75 wt%),8.44 μm(1.00 wt%)and 7.81 μm(1.25 wt%)respectively,the CI at 30 d decreased from 21.79% to 0% and the retention of curcumin increased from 80.45% to 90.05%.The higher the concentration of WPI-MKSCNFs complexes during simulated in vitro digestion,the more structurally intact the emulsion droplets remain during digestion and the smaller the particle size.The release of free fatty acids decreased with increasing concentration of WPI-MKSCNFs complex,from 72.50% to59.49%,indicating that the unique reticular structure of WPI-MKSCNFs had a delaying effect on lipid digestion without "over-protection".The bioacessability of curcumin increased with increasing concentration of WPI-MKSCNFs,and the bioacessability of curcumin was 74.80% at Pickering emulsion prepared with 1.25 wt% of WPIMKSCNFs complex.Therefore,the WPI-MKSCNFs emulsion system can achieve a better controlled release of curcumin,which is beneficial for its application in food and pharmaceutical applications.