Characterization of bacteriocin-coated antimicrobial polyethylene films by atomic force microscopy.

Antimicrobial agents can be used to give antimicrobial properties to polymeric materials used to envelope foods for packaging purposes. In this study, we exploited an atomic force microscopy (AFM) analysis for the characterization of plastic films activated with antimicrobial agents. The aim was to acquire information on the distribution of the antimicrobials on plastic materials with the ultimate scope of understanding the mechanisms of interaction between antimicrobials and materials to be used for food packaging. Four polyethylene films differing in linear, EVA, and erucamide content were activated by 3 different bacteriocins as antimicrobials, namely, nisin and bacteriocins Bac162W from Lactobacillus curvatus and BacAM09 from Lactobacillus plantarum. The spectrum of activity of the bacteriocins was assayed and shown to include several strains of Listeria monocytogenes. The plastic films were activated by a previously developed coating procedure and the surfaces of the active films were examined by AFM. In addition, roughness parameters related to the single surfaces were investigated by an appropriate software. Significant differences were found between the bacteriocin activated and control (nonactivated) films and the activated surfaces showed lower values of average roughness and surface area ratio. It was not always possible to obtain a homogeneous distribution of the bacteriocin preparation following the coating procedure. This result was dependent on the bacteriocin used and its distribution on the different plastic films. Overall, the bacteriocin Bac162W showed the most homogeneous distribution while surfaces treated with nisin, showing a sort of microtexturing, always gave the highest roughness values. Although the issue needs further investigation, the connection between AFM imaging, roughness, and antimicrobial distribution on active packaging showed the potential to improve the understanding of the interactions between plastic films and antimicrobial preparations that can be important for the innovation in food packaging and science.

Antimicrobial activity of a nisin-activated plastic film for food packaging.

AIMS: To determine the effectiveness of a packaging film coated with nisin to inhibit Micrococcus luteus ATCC 10240 in tryptone soya broth (TSB) and the microbiota of raw milk during storage. A further aim was to examine the release of nisin from the activated film. METHODS AND RESULTS: An active package, obtained from nisin-treated film, was filled with 1 l of M. luteus ATCC 10240 (ML) suspension in TSB and stored at 4 and 25 degrees C for 2 days. After 24 h at 25 degrees C there was a remarkable reduction of M. luteus ATCC 10240 compared with the control, while at 4 degrees C a slight reduction was observed. Moreover, microbial growth was controlled when 1 l of three different kinds of milk was poured into the active package and stored at 4 degrees C for 7 days. The most significant results were observed in raw milk and pasteurized milk with a reduction of 0.9 log and 1.3 log, respectively. The release experiments showed that nisin release from the film was unpredictable, but it was favoured by low pH and high temperature. CONCLUSIONS: It appears that nisin-coated films were effective in inhibiting M. luteus ATCC 10240 in TSB and the bacterial flora in milk, and the release of nisin was pH and temperature dependent. SIGNIFICANCE AND IMPACT OF THE STUDY: Nisin-activated film may control bacterial growth, maintaining food quality, safety and extending the shelf-life of food products.

Development of polythene films for food packaging activated with an antilisterial bacteriocin from Lactobacillus curvatus 32Y.

AIMS: The aims of this work were to (i) use a bacteriocin produced by Lactobacillus curvatus 32Y active against Listeria monocytogenes to activate polythene films by different methods, (ii) implement a large-scale process for antilisterial polythene films production and (iii) verify the efficacy of the developed films in inhibiting the growth of L. monocytogenes during the storage of meat products. METHODS AND RESULTS: The film was made active by using the antilisterial bacteriocin 32Y by Lact. curvatus with three different procedures: soaking, spraying and coating. The antimicrobial activity of the activated films was tested in plate assays against the indicator strain L. monocytogenes V7. All the used procedures yielded active polythene films although the quality of the inhibition was different. The coating was therefore employed to develop active polythene films in an industrial plant. The antimicrobial activity of the industrially produced films was tested in experiments of food packaging involving pork steak and ground beef contaminated by L. monocytogenes V7 at roughly 10(3) CFU cm(-2) and gram respectively. The results of the challenge tests showed the highest antimicrobial activity after 24 h at 4 degrees C, with a decrease of about 1 log of the L. monocytogenes population. CONCLUSIONS: Antimicrobial packaging can play an important role in reducing the risk of pathogen development, as well as extending the shelf life of foods. SIGNIFICANCE AND IMPACT OF THE STUDY: Studies of new food-grade bacteriocins as preservatives and development of suitable systems of bacteriocin treatment of plastic films for food packaging are important issues in applied microbiology and biotechnology, both for implementing and improving effective hurdle technologies for a better preservation of food products.