טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShemesh Rotem
SubjectDevelopment and Characterization of Polymer Systems with
Antimicrobial Activity
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Professor Ester H. Segal
Full Thesis textFull thesis text - English Version


Abstract

Antimicrobial packaging is a promising form of active packaging that can inhibit microorganism growth in order to maintain product quality and safety. One common approach for designing such systems is based on the release of volatile antimicrobial agents from the packaging material into the food or the packaging headspace. The emergence of antibiotic resistance of pathogenic bacteria has led to renewed interest in exploring the potential of plant-derived antimicrobials e.g., essential oils (EOs), as an alternative to synthetic compounds. EOs are natural substances, recognized as GRAS (Generally Recognized as Safe), characterized by antimicrobial activity against a wide range of microorganisms, including bacteria, yeast and molds. However, the high volatility of these compounds presents a major challenge in their incorporation into polymers by conventional high-temperature processing techniques, while maintaining their antimicrobial activity for a desired shelf life. This study presents a new approach for overcoming these challenges by using nano-scale clays as functional carriers for EOs. The carriers intercalate or encapsulate the EOs, protecting them and allowing their preservation during high-temperature compounding processes. Herein, we employ organo-modified montmorillonite (MMT) clays or Halloysite nanotubes (HNTs) as nano-carriers for carvacrol (used as a model EO). Thus, a pre-compounding step in designed to promote loading of the carvacrol into the different clays to produce MMT/carvacrol and HNTs/carvacrol hybrids are produced. This pre-compounding encapsulation step imparts enhanced thermal stability to the carvacrol, allowing for its subsequent melt compounding within different polymers i.e., low-density polyethylene and polyamide 6. The resulting polymer nanocomposites exhibit outstanding antimicrobial properties with a broad spectrum of inhibitory activity against Escherichia coli, Listeria innocua and wide range of fungal molds. The use of the nano-scale carriers not only hinders the substantial carvacrol loss during processing but also delays its out-diffusion from the nanocomposite and allows for a prolonged antimicrobial activity. The antimicrobial effectiveness of these nanocomposites is successfully demonstrated in complex model food systems (soft cheese, bread and various fresh produce). Thus, these new active polymer nanocomposites presents an immense potential in controlling microbial contamination and in a global effort to reduce food loss and waste.