Abstract
Abstract Films were prepared with 0.2% (w/v) gellan gum, 1% (w/v) citric pectin, 0.5% (w/v) glycerol, 5 mM CaCl2, 0.05 M Ethylenediaminetetraacetic acid (EDTA), and different concentrations of an antimicrobial activity-concentrated supernatant (AMC) obtained from fermentations of Streptococcus infantarius, which produces bacteriocin-like inhibitory substances (i.e., treatments F1, F2 and F3 with 75, 90 and 120 arbitrary units (AU)/mL, respectively). The treatments were based on a minimum-inhibitory-concentration (i.e., AMC, 90 AU/mL, plus EDTA, 0.05 M) for Escherichia coli, Staphylococcus aureus and Listeria monocytogenes growing in brain-heart-infusion medium at 35 °C. The films hindered the bacterium growth in selective media: E. coli -MacConkey, S. aureus-Baird Parker and L. monocytogenes -Oxford, during 30 days at 25 °C. Moreover, the F2 films entirely inhibited the growth of the tested bacteria in a Mexican cheese medium, in 7-day cultures at 35 °C; contrariwise, controls with no film exhibited bacterial growths in the range 107 -109 CFU/g. The physical-mechanical properties of the films were changed by the addition of EDTA-AMC, being (F2 film)/(control-film with no AMC nor EDTA): Young’s modulus (MPa), 1,394/707; Elongation at break (%), 1.9/9.3; Stress at break (MPa), 5.7/12.6; Water Vapour Permeability (10-11 g m Pa-1 s-1 m -2), 3/20, and Oxygen Permeability (10-12 g m Pa-1 s -1 m-2), 1.9/1.2.
Highlights
The food packaging research is of worldwide interest due to food safety matters, among others (Campos et al, 2010)
Foodborne disease episodes due to cheese consumption have occurred affecting people. Examples of this are: cheese related listeriosis outbreaks in Austria, Germany and Czech Republic (Fretz et al, 2010), Portugal (Magalhães et al, 2015) and USA (Silk et al, 2013); Escherichia coli O157:H7 infection associated with fresh cheese curds in Wisconsin (Durch et al, 2000); Staphylococcus aureus food poisoning outbreaks linked to raw milk semi-hard, raw milk soft, sheep’s milk and sliced soft cheese in France (13 outbreaks were reported by Kérouanton et al (2007) between 1981 and 2002)
In order to increase the antimicrobial spectrum in bacteriocin applications, they are frequently used in combination with other agents, as the chelator Ethylenediaminetetraacetic acid (EDTA), which contributes to make the bacterium outer membranes more permeable
Summary
The food packaging research is of worldwide interest due to food safety matters, among others (Campos et al, 2010). Foodborne disease episodes due to cheese consumption have occurred affecting people Examples of this are: cheese related listeriosis outbreaks in Austria, Germany and Czech Republic (Fretz et al, 2010), Portugal (Magalhães et al, 2015) and USA (Silk et al, 2013); Escherichia coli O157:H7 infection associated with fresh cheese curds in Wisconsin (Durch et al, 2000); Staphylococcus aureus food poisoning outbreaks linked to raw milk semi-hard, raw milk soft, sheep’s milk and sliced soft cheese in France (13 outbreaks were reported by Kérouanton et al (2007) between 1981 and 2002). Some biopolymers do exhibit an antimicrobial activity, that would contribute to a more effective antimicrobial food packaging. This is the case of pectins (Calce et al, 2014; Jindal et al, 2013) and chitosan (Aider, 2010)
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