Preparation Of Dihydromyricetin-Ag~+ Nanoemulsion And Study On Its Bacteriostatic Performance And Mechanism

Food safety caused by pathogenic microorganisms is a huge challenge,which needs to be dealt with since the new century.Safer and more environment-friendly food bacteriostatic agents need to be developed.Dihydromyricetin(DMY)is a natural product with a variety of physiological activities.It has excellent bacteriostatic ability but poor solubility in water,which has become a problem for its application in the food industry.Ag~+is the metal ion with the strongest bacteriostatic ability,but it can also cause harm to normal human cells under high concentration conditions,and the concentration detected by laws and regulations cannot effectively inhibit bacteria.This has also become an obstacle to its application in the food industry.This article proposes a method by constructing a nanoemulsion system,using Ag~+as the water phase,and dihydromyricetin as the oil phase to be included in the hydrophobic core of the emulsion to achieve the effect of solubilization.At the same time,dihydromyricetin and Ag~+play a synergistic antibacterial effect,achieving efficient bacteriostatic performances while avoiding safety issues caused by high concentrations of Ag~+.The main findings of this article are as follows:(1)An emulsion system was prepared,and it was confirmed that the dihydromyricetin and Ag~+did not chelate through full-wavelength scanning of ultraviolet and visible light,but was formed in the form of an emulsion.The outer layer of Ag~+was connected to the hydrophilic end of the surfactant.Dihydromyricetin is wrapped in a hydrophobic core connected to the hydrophobic end of the surfactant,and its average particle size is 211.5 nm.In addition,since the droplets of the emulsion was observed as regular circles under the transmission electron microscope,and the particle size distribution of the system shows multiple broad peaks,it is considered that the system forms a nanoemulsion rather than a microemulsion.(2)Bacteriostatic experiments confirmed that the minimum inhibitory concentration(MIC)of dihydromyricetin against S.aureus and E.coli was 1.25 mg/m L.A composite emulsion prepared with dihydromyricetin at a concentration of 1.25 mg/m L and Ag~+was found to be effective against gold.The bacteriostatic performance of S.aureus and E.coli is significantly improved compared to that of dihydromyricetin or Ag~+alone,and the synergistic purpose is achieved.(3)Further research on the bacteriostatic mechanism of S.aureus and E.coli.It is believed that the reason for the synergistic effect of the nanoemulsion may be that(1)the outermost layer Ag~+of the nanoemulsion first destroys the cell membrane or cell wall,and then released dihydromyricetin have better access to these cells;(2)The formation of nanoemulsion increases the solubility and stability of dihydromyricetin,it can be uniformly dispersed in the system,and the contact area with cells is larger,so nanoemulsion can showed an ideal synergistic inhibitory effect;(3)Because of the synergistic effect of dihydromyricetin and Ag~+a,the adhesion speed and damage strength to the bacterial cell wall and cell membrane was Accelerated.In addition,from the observation by TEM,it can be seen that the morphological changes of the two bacterial cells after contacting with the nanoemulsion are not the same.The reason may be due to the difference in the cell wall structure of Gram-negative bacteria and Gram-positive bacteria.(4)The inhibitory effect of dihydromyricetin on Candida albicans was studied.By changing the culture conditions of Candida albicans,it was found that the three types of culture medium,culture temperature,and p H value have a great influence on its morphological transformation.The liquid culture medium,higher temperature and p H are all conducive to the induction of mycelial state.Akaline p H conditions will promote the mycelial state to return to the yeast state.The most suitable temperature for Candida albicans to develop hyphae is 37?,and the p H is about 7.Inhibition experiments of dihydromyricetin on Candida albicans revealed that the MIC of dihydromyricetin against Candida albicans was 2.5 mg/m L,and it was found that low concentration of dihydromyricetin can promote the growth and proliferation of the bacteria.The synergistic antibacterial effect of nanoemulsion on Candida albicans was found to be different in different media,which may be related to the regulation of the expression of certain genes.In addition,by observing the morphological changes of Candida albicans after contact with the nanoemulsion,it was found that the integrity and permeability of the cell wall and cell membrane of the nanoemulsion and dihydromyricetin were greatly damaged.It is thought that it may be related to the ability of polyphenols to reduce the synthesis of ergosterol,the main component of cell membranes.