Edible films and coatings are increasingly being used as carriers of functional additives including antimicrobial agents. Consumer interest in naturally-derived antimicrobials has also increased. Plant extracts such as grape seed and green tea extracts are known to have antiviral as well as antibacterial activities. Even though there are several researches that have investigated the use of edible films and coatings as carriers of antimicrobial agents against foodborne bacterial pathogens, unfortunately data is lacking on the use of these same technologies on foodborne viruses. Therefore, this study seeks to develop edible films and coatings that can control foodborne viruses. The film’s antibacterial and mechanical properties were also tested. Chapters 1 and 2 introduce and review previous researches in edible films and coatings. Topics such as the types of biopolymer, film formation methods and mechanisms, foodborne viruses and bacteria, as well as edible film characterization and properties are discussed.
Chapter 3 of this study investigated the virucidal activity of green tea extract (GTE) dissolved in deionized water and also incorporated into chitosan film forming solutions (FFS) and into chitosan films. For comparison, the antibacterial activity of the films was also investigated against Listeria innocua and Escherichia coli K12. The viral infectivity after treatments was measured by plaque assays. The 1, 1.5 and 2.5% aqueous GTE solutions significantly (p<0.05) reduced murine norovirus (MNV-1) plaques by 1.69, 2.47, and 3.26 log after 3 h exposure, respectively. Similarly, the FFS containing 2.5 and 5.0% GTE reduced MNV-1 counts by 2.45 and 3.97 log10 PFU/ml, respectively
after 3 h exposure. Additionally, the edible films enriched with the GTE (5, 10 and 15%) were also effective against MNV-1. After a 24 h incubation period, the 5 and 10% GTE films significantly (p<0.05) resulted in MNV-1 titer reductions of 1.60 and 4.50 log10 PFU/ml, respectively. The film containing 15% GTE reduced norovirus plaques to undetectable levels in 24 h. Finally, all the GTE films (5, 10 and 15%) reduced L. innocua and E. coli K12 populations to undetectable levels in tryptic soy broth after 24 h exposure.
Chapter 4 investigated the effect of grape seed extract in solution, and in edible coatings and films against MNV-1. Also, the films were tested against L. innocua and E. coli K12, surrogates for L. monocytogenes and E. coli O157:H7, respectively. Grape seed extract concentrations of 1, 1.5 and 2.5% dissolved in deionized water resulted in MNV-1 plaque reductions (p<0.05) of 1.75, 2.60 and 3.58 log10 PFU/ml, respectively, after 3 h. The chitosan solutions incorporated with the GSE (2.5 and 5%) also reduced MNV-1 titers significantly (p<0.05) by 2.68 and 4.00 log10 PFU/ml, respectively, after 3 h. Additionally, incorporation of the GSE into the chitosan films enhanced its efficacy against MNV-1, L. innocua and E. coli K12. The chitosan films containing 5, 10, and 15% GSE showed reductions of 0.92, 1.89 and 2.27 log10 PFU/ml, respectively after 4 h of incubation. Also after 24 h, the 5 and 10% GSE films reduced MNV-1 titers by 1.90 and 3.26 log10 PFU/ml, respectively, while the 15% GSE film reduced MNV-1 to undetectable levels. For E. coli K12, there were reductions of 2.28, 5.18 and 7.14 log10 CFU/ml after 24 h exposure by the 5, 10, and 15% GSE films, respectively. Also, L. innocua counts were reduced by 3.06, 6.15 and 6.91 log10 CFU/ml by the 5, 10 and 15% GSE films, respectively.
The final part of this dissertation (chapter 5) investigated the effect of glycerol, GTE and GSE on the mechanical and moisture barrier properties of chitosan film. To optimize the quantities of glycerol, GTE and GSE in the chitosan film samples, the tensile strength (TS), percent elongation at break (%E), thickness, moisture content, water vapor permeability and solubility were determined for each treatment combination. The results showed that, TS significantly (p<0.05) decreased after the incorporation of glycerol. The tensile strength of 2% chitosan (used as the control) was 48.09 ± 5.17 MPa. The films incorporated with GTE or GSE and glycerol were significantly (p<0.05) lower in TS compared to the control. Values of 11.07 ± 2.50, 6.42 ± 0.68 and 6.55 ± 0.80 MPa were recorded for the 5, 10, and 15% GSE films, respectively. For the 5, 10 and 15% GTE films, TS values of 12.48 ± 2.52, 5.43 ± 0.59 and 5.07 ± 1.27 MPa were obtained, respectively. Also, the %E obtained for the 2% chitosan control film was 4.98 ± 0.94. The 5, 10 and 15% GSE films produced %E values of 16.75 ± 2.02, 30.95 ± 6.92 and 30.22 ± 4.98%, respectively. The values obtained for the 5, 10, and 15% GTE films were 23.77 ± 3.30, 39.12± 4.27 and 43.49 ± 1.06%, respectively. The WVP of chitosan film without the extract was 0.349 ± 0.039 g.mm/m2.h. kPa. The 5, 10, and 15% GTE films produced WVP values of 0.417 ± 0.007, 0.457 ± 0.005 and 0.569 ± 0.025 g.mm/m2.h. kPa, respectively. Also, the 5, 10 and 15%GSE films recorded WVP values of 0.422 ± 0.085, 0.496 ± 0.083 and 0.524± 0.029 g.mm/m2.h. kPa, respectively.