Antimicrobial peptide immobilization on natural supports

CAROLINA IBARGUREN

Hamburgo

Encuentro; Alexander von Humboldt Foundation Network Meeting; 2011

Alexander von Humboldt Foundation

The main focus of this work lies on the development of immobilized nisin systems using natural clay as a support structure. The aim is to produce food grade material capable of releasing antimicrobial agents. Montmorillonite (MMT), a natural abundant inexpensive solid approved by the FDA as a food additive, has been selected as support. This hydrated alumina-silicate layered clay consists of an edge-shared octahedral sheet of aluminum hydroxide between two silica tetrahedral layers with imbalanced surface negative charges compensated by exchangeable cations (typically Na+ and Ca+2). This type of clay is characterized by a moderate negative surface charge (cation exchange capacity, CEC) and a high surface area. The antimicrobial agent to be immobilized is nisin, a polypeptide bactericin synthesized by Lactococcus lactis subesp. lactis which presents antimicrobial activity against several food pathogens, such as Listeria monocytogenes. Structurally, it is a 34 amino acid polypeptide, presenting cationic and hydrophobic characteristics, with a molar mass of 3500 Da. The aim is to first study the peptide-carrier interaction using a commercial bacteriocin (nisin E234) and then extend this knowledge to other bacteriocins that are in the proccess of characterization by the research group in Argentina. To achieve suitable immobilized bacteriocin preparations for the bio protection of food, different variables (pH, temperature, concentration of the support suspension, peptide concentration, etc.) that condition the acquisition of stable and active antimicrobial systems will be studied by characterizing natural and nisin incorporated supports. This will allow the development of a nisin-montmorillonite system that could have application on food in which L. monocytogenes has a negative impact. The characterization will be performed during the stay in Germany at the IMT by using the following techniques: X-Ray Diffraction (XRD), X-ray Photoelectron-Spectroscopy (XPS), specific surface area determination (BET method), Thermodifferential and Thermogravimetric Analysis (DTA-TG), FTIR Spectroscopy, Scanning Electron Microscopy (SEM-EDX), Transmission Electron Microscopy (TEM-EDS), Zeta potential measurement. Once characterized, the residual antibacterial activity achieved in the nisin immobilized systems will be evaluated in Argentina. The internship will allow the acquisition of experience in handling different equipment necessary for the characterization of surfaces, most of which are not available in the current workplace in Argentina. Some possible options of regional interest in Salta, Argentina, could be the addition of antibacterial agents as a biopreservative during the elaboration of dairy goat products (mainly fresh milk and cheese); as a biopreservant of goat milk powder, a product that has not been developed yet locally, but that is important to satisfy the demand of the population intolerant to cow´s milk; and on the development of films modified with the addition of bacteriocin adsorbed clay, so that the introduction of clay optimizes film permeability properties besides the antimicrobial effect.