Preparation,Characterization And Application Of The Food-grade Gelatin Pickering Emulsion Based On Genipin Cross-linking

Rentently,Pickering emulsion,stabilized by solid particles instead of surfactants,has attracted wide attention due to its outstanding characteristics in food,pharmaceutical,chemical,material engineering and other fields,such as low cost,environmental protection,controlled release of components,extraordinary stability against coalescence and lipid oxidation.Gelatin has many applications in improving food structure,water holding capacity and stability.Gelatin has been used to prepare gelatin nanoparticles(GNPs)and stabilize Pickering emulsion due to the low cost and good biocompatibility.However,the preparation methods of GNPs involved in toxic reagents such as glutaraldehyde and acetone,which hampered the green applications of the GNPs and the stabilized Pickering emulsion in food,medicine,cosmetics and other fields.Genipin is a natural covalent cross-linking agent hydrolyzed from natural gardenoside by ?-glucosidase.It can interact with free amino groups of proteins(Schiff base reaction)and be used as food-grade cross-linking agent.Therefore,the food-grade GNPs were prepared by a two-step desolvation method by using gelatin(type B)as raw material,ethanol as desolvent agent and genipin as a cross-linker.The effect of pH and genipin dosage on GNPs were investigated.On this basis,the effect of GNPs concentration on the properties of Pickering emulsion was evaluated systematically,and the environmental stability of Pickering emulsion and the application of ?-carotene load were investigated.The purpose of this study is to provide a theoretical basis for the development and application of food-grade Pickering emulsion based on gelatin.The detailed results are showed as follows:(1)The food-grade gelatin nanoparticles(GNPs)were prepared by a two-step desolvation method and using genipin as a cross-linker.The results showed that the GNPs with well dispersed and uniform was not easy to prepare due to the weak electrostatic repulsion at pH 8 ? 11.The GNPs with narrow size distribution and well dispersion could be obtained only at pH 12.Furthermore,Furthermore,the crosslinking degree of the GNPs increased with the increasing dosage of genipin,thus leading to a more obvious cross-linking morphology observed from SEM.The obtained GNPs showed a good dispersibility and uniformity with a size range of 386 ? 438 nm.However,the GNPs cross-linked by 8 wt% genipin dosage revealed a relatively higher size because of the aggregation induced by hydrogen bond.The 10 wt% group had good thermal stability and storage stability.The optical microscopy results showed that the Pickering emulsions(30 ? 50 vol% internal phase)stabilized by the GNPs had good uniformity and stability,even after 30 days of storage time(4 ?),suggesting that the stable GNPs had great potential in food-grade Pickering emulsion.(2)The properties of Pickering emulsion stabilized by different GNPs concentrations(0.3 ? 2.0%)were investigated systematically,including the optical microscopy,droplet size,flocculation index(FI),rheological behavior,water holding capacity(WHC),protein adsorption rate(AP),interface protein content(?),interfacial pressure(?)and microstructure(CLSM).The results showed that increasing GNPs concentration could obviously increase the ? value of GNPs,thus inducing more GNPs adsorbing(AP and ?)at the oil-water interface and participating in the formation of network structure(CLSM),consequently resulting in a smaller droplet size and FI of the stabilized Pickering emulsion.Furthermore,the increase of AP resulted in the increase of apparent viscosity and modulus,and formed a more compact network structure,thus improving the WHC and stability of the Pickering emulsion.Therefore,different properties of the Pickering emulsion could be adjusted by changing the GNPs concentration.The Pickering emulsion with relatively low viscosity,good mobility and stability could be prepared at 0.5 wt% GNPs concentration,the Pickering emulsion with high viscosity and stability could be prepared at 1.0 wt% GNPs concentration,and the Pickering emulsion with prominent viscoelasticity and stability could be prepared at 1.5 wt% GNPs concentration.This study could provide important implications for the development and application of food-grade Pickering emulsion based on gelatin.(3)The pH,ionic strength,heat and freeze-thaw stability of Pickering emulsion stabilized by 1.0 wt% GNPs were studied systematically.The results showed that a relatively stable emulsion could be formed when the pH of GNPs dispersion was 7,and 9.However,the stable Pickering emulsion could hardly be formed under acidic conditions due to the weak electrostatic repulsion,especially when pH is 5.The addition of NaCl resulted in the generation of electrostatic shielding,which made the droplet size and CI increased(0 ? 50 mM).With the further increased of NaCl(100 ? 500 mM),more particles were attracted to the oil-water interface and participated in the stability of the interface due to the increase of surface charge,which improved the interaction between the droplets and made the droplet size relatively smaller and stable.After heating(70? and 100?),the droplet size and the creaming of Pickering emulsion increased obviously,but no demulsification occurred.Pickering emulsion was not resistant to freeze-thaw due to the interfacial film and the network structure formed by hydrogen bonds were destroyed by the formation of ice crystals.Furthermore,the three properties of Pickering emulsion in the previous study(relatively low viscosity,good mobility and stability;high viscosity and stability;prominent viscoelasticity and stability)were applied to the loading system of ?-carotene.The results showed that the high viscoelastic Pickering emulsion could significantly reduce the photodegradation of ?-carotene,the ?-carotene was remained at the highest level(? 70%)and even after 30 days of storage.The results of vitro digestion experiments showed that the Pickering emulsion inhibited the accumulation of oil droplets and oil droplets to a certain extent due to the high viscosity,thicker interfacial adsorption layer and dense network structure,thereby reduced the release rate and release of FFA,increased the retention of ?-carotene in micellar phase,thereby increasing the bioaccessibility of ?-carotene.