Antibacterial Mechanism Of ε-polylysine Against Staphylococcus Aureus And Its Effect On The Application Of Milk

To seek for new, efficient and safe natural preservatives, explore the inhibition mechanism of ε-Polylysine (ε-PL) against Saphylococcus aureus(S. aureus) and preservative effects of s-PL applied in food, this study introduced briefly the basic properties of s-PL and milk, and researched the effects of ε-PL on cell wall, morphological structure and cell membrane. Additionally, the preservative effect of ε-PL on milk was discussed. And these results were obtained as follows:(1) Preservative effect of ε-PL against S. aureus was determined through Oxford cup method to measurethe diameters of inhibition zones of S. aureus,treating by different concentration of ε-PL. The morphology changes of S. aureus treated with 400μg/mL ε-PL and without c-PL for 4h,8h, respectively, were evaluated by atomic force microscope analysis.The results showed that the diameters of inhibition zones became larger with increasing concentration of ε-PL, indicating ε-PL had significant preservative effect against S. aureus. Futhermore, the preservative effect and the concentration of ε-PL was positively correlated. S. aureus cells gradually appeared sag, fold, or even collapse, with extension of ε-PL treatment time.Thus, preservative effect of ε-PL against S. aureus enhanced with the increase of concentration and time.(2) The effects of different concentrations of s-PL on S. aureus showed that ε-PL could change S. aureus cell membrane structure, increase permeability of cell wall, increase outer membrane and cell membrane permeability, increase cell surface hydrophobicity, disrupt cell membrane protein structure, and hinder the synthesis of membrane protein or degarade membrane protein, leading to interference of cell normal physiological activities and damaging normal cell morphology, disturb cell balance. Therefore, growth of S. aureus was inhibited and even death, in addition, the impacts increased with increasing ε-PL concentrations.(3)The effects of s-PL on S. aureus cells indicated that ε-PL could damage the normal structure of S. aureus cells, cause the leakage of β-galactosidase, respiratory chain dehydrogenase, K+, Ca2+, Mg2+, and decrease the activity of respiratory chain dehydrogenase, hinder the synthesis of the cell protein and degrade protein, interfere with the normal synthesis of DNA, damage cells DNA instructive, and cause the leakage of DNA, RNA in S. aureus cells. Besides, the influence increased with increasing concentration of ε-PL, eventually inhibiting the normal growth of S. aureus, or even killing bacteria.(4) The aim was to research application effect of ε-PL on milk during storage.Compared to control, ε-PL could effectively inhibit the decrease of lactose and milk protein, inhibit the increase of milk acidity, delay clotting time of milk and reduce the total bacterial count.These results indicated that ε-PL could significantly inhibit the growth and reproduction of bacteria, maintain normal physical and chemical indicators of milk and extend its shelf life. Therefore, ε-PL could be used as an excellent preservative in milk and has high research value.