Food borne microorganisms, especially foodborne pathogens, result in significant illness and deaths. However, conventional food contact materials, such as plastic, paper, wood, stainless steel, etc., for food packaging are vulnerable to initial pathogen attachment and subsequent biofilm development. And numerous efforts for antimicrobial and anti-fouling food packaging suffer from low stability, high cost, loss of food taste, and leakage of bactericidal reagents. Herein, we propose to develop an antimicrobial food packaging material based on the visible-light-responsive graphitic carbon nitride (g-C₃N₄) and one earth-abundant biopolymer, chitosan. The antimicrobial potential of g-C₃N₄ against biofilms and planktonic bacteria under visible light irradiation has been well demonstrated in previous studies. After being incorporated into chitosan, a flexible polymeric composite film with promising antimicrobial effectiveness and robustness was achieved. Our study aims to understand the bactericidal mechanism of the composite under visible light irradiation and to seek opportunities to utilize the material for food packaging.
g-C₃N₄ powder was first prepared via thermal polycondensation of melamine, cyanuric acid, and barbituric acid with an optimized ratio to achieve desired photocatalytic performance, and the powder was added to the chitosan matrix to fabricate the g-C₃N₄/chitosan composite. The properties of the composite were characterized by Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). The results of confocal laser scanning microscopy (CLSM), SEM, and optical coherence topography (OCT) demonstrated that the composite material inhibited Staphylococcus epidermidis and Pseudomonas aeruginosa biofilms formation under the irradiation of visible white light emitting diodes (LEDs). Moreover, mature biofilms were removed from the surface of composite films after exposure to white LED light. The reactive oxygen species (ROS), i.e. singlet oxygen and superoxide anion radicals, identified during the photocatalytic process are believed to play an important role in biofilm inhibition and removal. In addition, the effectiveness of the composite material against the notorious foodborne pathogen, Escherichia coli O157:H7, is also very promising. Our study will have great impacts in food industry, by developing a new generation of antimicrobial food packages to protect public health.

John Lafleur

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