| Nisin is a natural antibacterial polypeptide which is produced by lactic acid bacterium (Lactoccocus lactis subsp. Lactis), composing of 34 amino acid residues. Due to efficient antibacterial activity, especially showing a strong inhibition against Gram-positive bacterium, nisin is one of the most popular natural antibacterial agents, and the only approved preservative bacteriocin used in food by the FDA. However, there are limitations. Nisin has a narrow antibacterial spectrum, only actively against gram-possitive bacterium, for gram-negative bacterium and fungi microbes basically no antibacterial effect; In addition, when applying to food products, due to the interaction of some components in food with nisin, its activity will be greatly reduced. However, nisin itself can be combined with many active substances, which is a significant approach of overcoming the deficiencies of narrow spectrum. Embedding nisin in appropriate package can also effectively prevent nisin from being affected and consumed by other substances in food dispersion medium, achieving an extended release time for sustained-release effect.This topic systematically studied antibacterial activity, synergistic effect and antibacterial mechanism of nisin and D-limonene. Then prepared a stable and even nanoemulsion delivery system containing both nisin and limonene, which not only improved the their antibacterial effect of nisin and D-limonene, extended the antimicrobial spectrum, but also reduces the addition of antimicrobial agent; preparation of nisin loading organogel system effectively improve the nisin antibacterial aging, improve utilization, achieved the following main results:1. Gradient dilution method was used to determine minimum inhibitory concentration (MIC) of nisin and D-limonene for the four tested strains, comparing the antibacterial activity of two antimicrobial agents; the synergistic effect of nisin and D-limonene was approved by checkerboard dilution method and inhibitory concentration index FICI assessment.2. Nanoemulsions containing nisin and D-limonene were prepared by low-energy phase transition method, the preparation process was optimized, dosage of surfactant with 8% (w/w) conditions, a 20nm particle size of nanoemulsion can be obtained; Antibacterial properties of nanoemulsion were also studied, antibacterial activity of composite nano-emulsion system has been significantly improved, which adding a significantly reduction of addition of the antimicrobial agents.3. Growth curves of four test strains were determined and investigated that nanoemulsion system have a significant influence on the growth condition of bacterium; Scanning electron microscopy for cell structure of four tests showed morphological changes under the nanoemulsions. Determination of release of cell contents proved the efficient antibacterial and mechanisms of action of antimicrobial nanoemulsion systems, indicating a proof of the role of the antimicrobial agent for the destruction of the cell membrane.4. Organogel systems containing nisin were prepared by using stearic acid as gelator, and its internal molecular structure was observed and analyzed under microscope. TGA has been applied to measure thermodynamic stability of organogel systems. It proved that addition of nisin to organogel didn't cause significant changes in the structure and properties, and no material loss in the temperature range.5. Nisin loading organogel microcapsules were prepared by SPG membrane emulsification. By measuring the particle size, effects of different emulsifiers have been valuated; Nisin release properties of nisin loading organogel microcapsules proved that organogel microcapsuls displayed a long period and sustained release performance.6. Antibacterial properties of the nisin loading organogel microcapsules were determined by measuration of growth curves of four test strains. It shows that, comparing with the addition of pure nisin, organogel microcapsules can inhibit the growth of strains for a long time with a sustained release. |
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