Starch-halloysite nanocomposites containing nisin: Characterization and inhibition of Listeria monocytogenes in soft cheese

Starch/halloysite/nisin nanocomposite films were developed as active antimicrobial packaging. Nano composites without nisin and control films (containing starch and glycerol only) were also prepared. Scanning electron microscopy revealed that all samples were homogeneous, halloysite nanotubes (HNT) were dispersed in starch matrix, and film surfaces denoted aggregates as higher amount of nisin was added. X-ray diffraction spectra displayed alterations in typical starch peaks after HNT and nisin incorporation, indicating a decrease in polymer crystallization. Mechanical properties were improved when HNT was incorporated, but inferior values of Young modulus and tensile strength were obtained with nisin addition. Thermal stability decreased for bionanocomposites containing nisin, which showed T-max values about 20 degrees C lower than films without nisin. The antimicrobial activity was tested against Listeria monocytogenes, Clostridium perfringens and Staphylococcus aureus in skimmed milk agar and all micro-organisms were inhibited by nanocomposites containing nisin. These active films were applied on Minas Frescal cheese surface previously inoculated with L. monocytogenes. After 4 days, antimicrobial nano composite films with 2 g/100 g nisin significantly reduced the initial counts of the bacterium and those with 6 g/100 g nisin completely inhibited L. monocytogenes. Results showed that nisin supported in starch/halloysite films can be an active and useful barrier to control food contamination. (C) 2015 Elsevier Ltd. All rights reserved.