Preparation Of Antimicrobial Materials Based On Biomacromolecules

Biomacromolecules refer to the organism’s organic molecules whose molecular weight reaches tens of thousands or upper, such as proteins, nucleic acids and high-molecular hydrocarbons. Compared with the synthetic polymer, biomacromolecule has many advantages, for example, a wide variety of sources, renewable, environment friendly, biocompatibility, biodegradability and so on. So biomacromolecule becomes more and more important in materials. With the improvement of technology and social economy, seeking for a healthy and clean life makes the development of novel antimicrobial materials urgently needed. In this paper, we studied two kinds of biomacromolecules, soy protein isolate (SPI) and lysozyme to prepare antimicrobial materials.SPI contains various kinds of amino acids, of which tyrosine makes up to2-3mol%. Two biochemical agents, guandine hydrocholoride (GuHCl) and dithiothreitol (DTT), were used to destroy the hydrogen bonds and disulfide bonds in SPI to obtain original SPI solution, and concentration or dilution was used to get the desired concentrations.The tyrosine in SPI (0.25wt%, pH=10) was used to reduce Ag+(0.20mmol/L) to prepare silver nanoparticles (AgNPs), using natural SPI as both reducing and stabilizing agent. This method is environmentally friendly and easy to handle. We explored the influence of pH and lighting to find that the pH of the reaction system is critical for the AgNPs formation, as only in the alkaline condition, the tyrosine in SPI can show the reducibility. On the other hand, AgNPs could be synthesized under dark-ness, but the process is rather time-consuming, therefore, light exposure is a key role of such a reaction, which can accelerate the process greatly.We used time-resolved UV-Vis and fluorescence to get the optimum reaction condition, white light (incandescent lamp,100W) for24h to get the mono-dispersed AgNPs with the the size of about7nm. SPI-AgNPs films were then obtained by adding as-prepared AgNPs solution to different amount of pristine2%(w/w) SPI solution. The weight contents of AgNPs in different samples were selected as1.0%,0.5%,0.2%, and0.1%. From the antibacterial test, it can be seen that the SPI-AgNPs films exhibited excellent antibacterial activity against both Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli). When the Ag content in the film was larger than0.5wt%, almost all of the bacteria were killed within2h. If the Ag content was a little bit lower (0.2wt%), also90%of bacteria were killed within2h, and were almost totally killed within12h. The SPI-AgNPs films still showed considerable antimicrobial activity even when the Ag content was only0.1%. It still killed80%E. coli and70%S. aureus within2h, and90%E. coli and85%S. aureus within12h. Also the SPI-AgNPs films showed distinct inhibition zone against both S. aureus and E. coli.Lysozyme is able to prepare AgNPs with the reducibility of tyrosine under white light, similar to SPI. We explored the influence of the mass ratio of lysozyme to Ag+(10:0.5,10:1,10:2,10:5,10:10,10:20and10:50) and light illumination time (5min,10min,20min,30min,60min,120min and180min) to get the optimum reaction conditions, lysozyme:Ag+=10:20(w/w) with white light (incandescent lamp,100W) illumination for120min. Under this condition, lysozyme is able to reduce all silver ion involved, also, capable of scattering and stabilizing the AgNPs (5-20nm) prepared to get the Ly-AgNPs hydrosol. Staphylococcus aureus (S. aureus, ATCC6538) and Escherichia coli (E. coli, CMCC44103) were chosen to evaluate the antimicrobial activity of Ly-AgNPs hydrosol. It can be seen that the Ly-AgNPs hydrosol exhibited excellent antibacterial activity against both S. aureus and E. coli. The minimal inhibitory concentration (MIC) of Ly-AgNPs hydrosol against both S. aureus and E. coli is8.52mg/L, and the minimum bactericidal concentration (MBC) of Ly-AgNPs hydrosol against S. aureus and E. coli were17.04mg/L and8.52mg/L respectively. Also the Ly-AgNPs hydrosol showed distinct inhibition zone against both S. aureus and E. coli. Lysozyme is well known as an excellent antibacterial agent, which is widely used in food and pharmaceuticals industry. Its bactericidal activity is hypothesized to reside in its muramidase activity to β-1,4glycosidic bond, leading to degradation of the peptidoglycan layer and reduction of the mechanical strength of the bacterial cell wall and eventually resulting in killing of bacteria by lysis. Lysozyme’s isoelectric point is10.7while soy protein isolate’s isoelectric point is4-5, so the protein chains are with endowed with opposite charges under neutral condition, attracting each other electronically. So we prepared the soy protein isolated-lysozyme (SPI-Ly) blended films. Bacillus subtilis (B. subtilis, ATCC6633), Staphylococcus aureus (S. aureus, ATCC6538) and Escherichia coli (E. coli, CMCC44103) were chosen to evaluate the antimicrobial activity of SPI-Ly films. It was found that the SPI-Ly films exhibited excellent antibacterial activity against B. subtilis, while insensitive to either S. aureus or E. coli. In order to improve it, Ethylene Diamine Tetraacetic Acid (EDTA) was incorporated to get the SPI-Ly-EDTA composite films, which showed distinct inhibition zone against B. subtilis, S. aureus and E. coli as to the iron-chelating ability of EDTA. The prepared edible antimicrobial film made of environmentally benign and renewable materials shows great application prospect as antimicrobial food packages or biomedical materials.Our work based on biomacromolecules, which is great for the low cost, regeneration, biocompatibility and biodegradability, the whole process was carried out under mild environment and room temperature, which is energy-efficient and eco-friendly. The materials prepared show broad-spectrum and efficient antibacterial properties, according with the ideas of green and efficiency.