Antimicrobial immobilization on natural and synthetic supports

IBARGUREN C; AUDISIO MC; SHAM E; FARFÁN TORRES, EM

Bariloche, Río Negro - Argentina

Otro; EULASUR Summer School and Workshop: Properties and Applications of Nanomaterials; 2010

EULASUR

OBJECTIVES Development of immobilized nisin systems focused on the production of antimicrobial agents releasing food grade material using natural and synthetic inorganic oxides as supports. BACKGROUND The immobilization of proteins on solid surfaces has an important role in biomedical, technological and environmental applications (1). Natural clay minerals have been used to immobilize amino acids, proteins and enzymes for different biological applications (2). Nisin is a food additive approved by the FAO/WHO and considered GRAS (Generally Regarded As Safe) by the FDA, signifying that its use in food is safe and harmless (3). Natural phyllosilicates are also considered safe food additives by the FDA. To our knowledge, there is no literature regarding the use of clays as supports for the deposition of nisin. Previous studies showed that immobilized nisin conserves a good antimicrobial activity when low hydrophobic supports such as synthetic silica were used. Clays have numerous advantages regarding this application: are inexpensive (due to the abundance of worldwide reservoirs), have a behaviour similar to silica (phyllosilicates), with the added advantage of being able to modulate hydrophobicity by surfactant modification processes, are used as food additives approved by the FDA, have been used as vehicles for controlled release of active ingredients of drugs with very good results (4, 5, 6, 7). MONTMORILLONITE: THE SORBENT Montmorillonite (MMT) is a hydrated alumina-silicate layered clay consisting of an edge-shared octahedral sheet of aluminum hydroxide between two silica tetrahedral layers. The imbalance of the surface negative charges is compensated by exchangeable cations (typically Na+ and Ca+2). The parallel layers are linked together by weak electrostatic forces. This type of clay is characterized by a moderate negative surface charge (cation exchange capacity, CEC) and a high surface area (8). NISIN: THE SORBAT Nisin is a polypeptide bacteriocin produced by Lactococus lactis subsp. lactis which presents antimicrobial activity against a wide range of Gram-positive bacteria, including many heat-resistant and spore-forming bacteria, such as Clostridium botulinum and Bacillus cereus. It is also active against other organisms that can cause food spoilage and pathogens associated with foods, such as Listeria monocytogenes. Structurally, it is a 34 amino acid polypeptide, presenting cationic and hydrofobic characteristics, (9) with a molar mass of 3500 Da. It presents important functional properties, i.e. acid tolerance, thermo stability at low pH and a specific bactericidal mode of action (10). THE SORBTION The proposal is to study the immobilization of nisin in clays (montmorillonite). The materials obtained will be characterized using FTIR, RAMAN, RXD, TDA-TG, ZETA POTENTIAL, SEM, and evaluated for potential use as food biopreservatives, measured by the residual antimicrobial activity against Listeria monocytogenes, a pathogen difficult to control in food due to its ability to grow at low temperatures, low pH and high NaCl concentrations.