Biodegradable, non-toxic, antimicrobial zein nanofibers produced by electrospinning for sustainable food packaging applications

Z. Aytac, R. Huang, N. Vaze, T. Xu, M.B. Chan-Park, K.K. Parker, P. Demokritou
Harvard University,
United States

Keywords: electrospinning, nanofibers, biopolymers, zein, antimicrobial agents, antimicrobial activity, food safety and quality

Summary:

Minimizing food waste and enhancing food safety and quality and extending the shelf life of food products is of great importance since food waste accounts for 30-50% of the food supply across the value chain. In addition, food-borne diseases is a major public health challenge and cause 48 million illnesses per annum globally. Food packaging plays an important role in enhancing food quality and safety. However, the excessive use of non-biodegradable synthetic polymers as package materials has become a major environmental nuisance. An emerging research theme in the food package area is the development of sustainable, non-toxic, biodegradable materials to enhance food safety and quality. In this study, first core nanofibers (zein-NF) were synthesized from zein, a nature-derived protein-based biopolymer, via one-step electrospinning process without using any toxic chemicals and cross-linking approaches. Such fibers were deposited on various substrates including aluminum foil and biodegradable cellulose-based films. Morphological characterization studies carried out by scanning electron microscopy (SEM) revealed the bead-free and uniform morphology of zein-NF. Zein-NFs have 140±40 nm of average diameter. Furthermore, the antimicrobial activity of single or combinations of nature-derived antimicrobials such as thyme oil, citric acid, nisin was assessed for a panel of food-related microorganisms such as E.coli and L.innocua. A cocktail of such antimicrobials with optimum efficacy was selected and contains 1% (w/v) thyme oil, 5% (w/v) citric acid, and 0.005% (w/v) nisin. This cocktail was incorporated into zein solution via direct solution integration method and electrospinning was performed to develop zein nanofibers with antimicrobial functionality (zein-cocktail-NF). SEM images showed that zein-cocktail-NF have bead-free morphology and 165±35 nm of average diameter. Chemical characterization of zein-NF and zein-cocktail-NF was carried out by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). FTIR and XRD revealed that antimicrobials were successfully incorporated into nanofibers and amorphous structure of nanofibers was intact after the incorporation of antimicrobials, respectively. Release kinetic studies were performed to decide amount of each antimicrobials released at room temperature for 10 days into food simulants including water, 3% acetic acid, and 50% ethanol for non-acidic aqueous, acidic aqueous, and fatty food, respectively. The antimicrobial activity of the nanofibers was assessed against food-related pathogens (E.coli and L.innocua) via direct contact assay. The results showed that zein-cocktail-NF exhibited ~3 and 5 logs of reduction in 1 hour against E. coli and L. innocua, respectively. In addition, zein-cocktail-NF is quite effective at inhibiting the growth of E. coli and L. innocua by 5 logs reduction in 24 hours. Future studies will include shelf life studies for selected food categories. The overall results suggested that zein nanofibers developed in this project can be used for development of sustainable food packaging materials and have great potential in enhancing food safety and quality and extending shelf life of food products.