| Eugenol with strong clove aroma,can enhance the aroma intensity and improve the aroma persistance,and has broad-spectrum antibacterial property and antioxidant ability,which is often used as the raw materials for preparation of food flavors and tobacco flavors.Besides,eugenol has some functional properties including stomach strengthening and blood pressure lowering.However,the application of eugenol in the food industry is restricted by the characteristics of high volatility,low water solubility and poor stability.Nano-encapsulation can not only improve the water solubility and stability of active ingredients,reduce volatility,but also can achieve the sustained-release purpose.Among them,protein-polysaccharide complex nanoparticles are a promising carrier for active ingredients due to the fact that they are easy to prepare and can be prepared in mild reaction conditions.However,they are susceptible to environmental factors such as pH,temperature and ionic strength,resulting in aggregation and precipitation.The nanoparticles crosslinked by tannic acid can not only avoid the use of chemical cross-linkers,but also can achieve a synergistic antioxidant effect.In this study,sodium caseinate and gum arabic were selected as raw materials to prepare nanoparticles.The effects of mass ratio of sodium caseinate to gum arabic,total polymer concentration and pH on the formation of the complex were first investigated.Eugenol nanoparticles were further prepared,and the effect of tannic acid on the nanoparticles was investigated.The research results provided a theoretical basis for the mechanism of interaction between polyphenols and proteins,and proposed new strategies for the study of food delivery systems stability.The turbidity method and dynamic light scattering were used to evaluate the effect of mass ratio of sodium caseinate to gum arabic,total polymer concentration,and pH on the interaction between sodium caseinate and gum arabic.The results showed that the optimal conditions for nanoparticle preparation were determined as followed: the mass ratio 1:2,the total polymer concentration 0.3%,and the pH 4.2.Based on these conditions,the particle size and Zeta-potential of the prepared blank nanocomplex were about 150 nm and-25 mV,respectively,and the polydispersity index(PDI)was less than 0.3.Heat treatment at 80°C for 30 minutes facilitated the formation of nanoparticles and the uniform dispersion of particles.The eugenol nanoparticles with higher encapsulation efficiency and better stability were prepared by means of core-wall ratio adjustment.Furthermore,the effect of tannic acid on the formation of nanoparticles was also studied.Results showed that when the core-wall ratio was 1:2 and the add amount of tannic acid was 0.05%,the encapsulation efficiency of eugenol nanoparticles reached about 70%.Meanwhile,the particle size and Zeta-potential were about 150 nm and-35 m V,respectively.In terms of dispersibility,the particle size distribution is Double peak distribution.Fourier transform infrared spectroscopy and fluorescence spectroscopy analysis results showed that eugenol was encapsulated in the complex nanoparticles through hydrogen bonding and hydrophobic interaction with sodium caseinate,while the interaction between tannic acid and sodium caseinate was mainly hydrogen bonding.Fluorescence spectroscopy indicated that the addition of tannic acid led to fluorescence quenching of sodium caseinate and its affinity with tryptophan residues was higher than that of tyrosine residues.The results of circular dichroism suggested that the addition of tannic acid led to an increase in the content of ?-helix and ?-sheet of sodium caseinate,and a decrease in the content of ?-turn and random coil.Transmission electron microscopy results showed that the nanoparticles were spherical,and tannic acid can induce the growth and aggregation of the nanoparticles.Additionally,the physicochemical properties of eugenol nanoparticles were analyzed.The results of thermogravometric analysis and antioxidant experiment showed that nano-encapsulation improved the thermal degradation property and antioxidant ability of eugenol,and tannic acid played an important role in synergistic anti-oxidation.After being crosslinked by tannic acid,the stability of the nanoparticles increased at pH 3.0,the thermal stability did not change significantly,and the NaCl stability decreased.After storage at 4°C for 15 days,the retention rates of eugenol in uncrosslinked and crosslinked nanoparticles were 66% and 77%,respectively.After crosslinking,the retention rate of eugenol in nanoparticles slightly increased.Additionally,all nanoparticles exhibited good controlled-release property in gastrointestinal tract.However,nano-encapsulation had a negative effect on the antibacterial ability of eugenol. |
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