Effect Of N-terminal Modification On Activity Of Nisin And Its Application In Antimicrobial Film

Microbial contamination is one of the main causes of food spoilage and foodborne diseases during food processing,storage,transportation and consumption.Nisin is a typical,efficient,and safe antimicrobial peptide.Preparation of nisin and NaCl has been widely used as preservative in the food industry.The activity of nisin is related to acting matrix,pH value and temperature.How to improve the antimicrobial activity of nisin has attracted more and more attention.Therefore,nisin was taken as the research object to study the effect of N-terminal modification on its antimicrobial activity in this subject.Staphylococcus aureus ATCC 6538 was used as the indicator bacteria.The properties and antimicrobial activity of the film grafted nisin were further characterized.In addition,this grafting method was applied in composite antimicrobial film.The main research contents and results are as follows:(1)The N-terminal of nisin was modified by genipin and grafted onto chitosan.The activity of the grafted products was studied by antimicrobial experiments.The results showed that the increase of p H significantly reduced the activity of nisin,and the activity of nisin was retained after modification.When nisin was crosslinked with genipin,antimicrobial activity increased at pH 7.2 and decreased at pH 6.0.The activity of nisin increased after crosslinking with low concentration of chitosan.Less chitosan provided fewer amino sites and increased local number density of nisin.When the local number density of nisin was high,adjacent peptides could cooperatively penetrate into the lipid membrane,enhancing the antimicrobial ability of nisin.(2)Nisin and chitosan were crosslinked by genipin to prepare antimicrobial film.Appearance,light transmittance,micro structure,swelling rate,water solubility,gas and water vapor transmission rate,mechanical properties,thermal properties and antimicrobial activity of the film were characterized.When the ratio of genipin in the antimicrobial film increased,color of the film deepened;light transmittance of the film decreased at different wavelengths;pore number and crosslinking degree of the film increased;swelling ratio and water solubility of the film decreased;oxygen,carbon dioxide and water vapor transmission rate of the film didn't change significantly;tensile strength of the film increased first and then decreased;elongation at break of the film decreased gradually;thermal stability of the film increased.It was verified that the prepared film had stronger antimicrobial activity compared with chitosan film and nisin can be applied in film by grafting.(3)Nisin,chitosan and fibrin were crosslinked by genipin to prepare antimicrobial film.Growth factors and ectoderm mesenchymal stem cells were loaded on the antimicrobial film to prepare composite antimicrobial film,which was used for anti-infection and repair of skin damage.The results showed that,after skin damage,the wounds of rats in the control group were more severely infected and the healing speed was the slowest;the wounds of rats in the common film group were infected and the healing speed was slower;inflammation caused by bacterial infection in the composite antimicrobial film group was less and the healing speed was faster.Compared with the common film group,the composite antimicrobial film group had higher expression levels of epidermal and dermal related proteins.The composite antimicrobial film has the ability to resist infection and repair skin damage faster and better.