Development of packaging materials for food industry based on silver nanoparticles
mong the priority areas of food technology are loss prevention, quality preservation and ensuring the biological safety of food at all stages of production and subsequent storage. One of the innovative ways to improve the safety of food is to introduce additives into the packaging material that have antimicrobial and antioxidant activity. This allows to provide additional reduction of microbiological risk due to slowing of growth of surface microflora. The main requirements for antimicrobial additives are their sanitary and hygienic safety in contact with food, multifunctionality and stability at all stages of packaging processing. The performance characteristics of packaging materials after the introduction of additives should be maintained.
The development of nanotechnologies has allowed the production of materials that have unique properties and make it possible to significantly increase the shelf life of food products [1–4]. Interest in silver nanoparticles and materials obtained with their use grows mainly because of the unusual physical characteristics of this metal [5–10]. Important properties of silver nanoparticles are bactericidal and antiviral activities, so they can be used to make packaging materials with biocidal properties. The main condition for the applicability of silver nanoparticles in the packaging industry is their ability to anchor on the surface and in the pores of the packaging material. This condition can be ensured by using different variants of the substrate, as well as different technologies for deposition nanoparticles on the surface of the material.
Synthesis of nanoparticles was carried out by reduction of an aqueous solution of silver nitrate. The structure and size of nanoparticles depends on the reaction conditions and the concentration of silver nitrate. To a solution of silver nitrate with a concentration from 0.0001 M to 0.005 M, the same volume of the reducing agent solution (from 0.001 M to 0.15 M) was added and the pH was adjusted to a predetermined value using a sodium hydroxide solution. The solutions obtained were processed in a microwave oven for 20 minutes at a temperature of 80 °C and a power of 700 watts. As the electron scanning microscopy shows (Fig.1), the resulting particles have a spherical shape with a diameter from 1 to 200 nm. The yellow color of the solution also indicates their spherical shape. The resulting particles are stable, do not precipitate and do not change color for several weeks.
The developed composition was applied to the packaging paper by spraying. The choice of paper was based on the fact that, compared to other materials for food packaging, such a substrate is environmentally safe, hygienic and rapidly decomposed naturally, which is especially important in the processing of waste. Samples of packaging paper processed with different concentrations of silver nanoparticles were examined using a low-vacuum scanning electron microscope with an energy dispersive X-ray spectrometer. According to the data of scanning electron microscopy and energy-dispersive microanalysis (Fig.2, Table 1), untreated packaging paper contains 64.69% of carbon and 35.31% of oxygen. After modification with a solution of nanoparticles, 7.88% to 21.21% of silver particles are formed on the surface of the treated paper, which are distributed rather unevenly (Table 1).
Antimicrobial action was evaluated by the degree of inhibition of bacterial growth through different incubation times compared to control samples. The results of the studies (Fig.3a) showed that a high growth of microorganisms is observed in the control samples. In samples treated with solutions of silver nanoparticles (Fig.3b–e) with a concentration of 0.001-0.005 M, the growth of microorganisms decreases. As the concentration of silver nanoparticles increases, the antibacterial properties of the packaging materials are improved. Antimicrobial properties of the modified samples persisted for all five days of the study (Table 2, Fig.4).
Fig.4 shows that mesophilic aerobic and facultative anaerobic microorganisms (Staphylococcus aureus) successfully reproduce on a control sample, but their growth slows down in samples treated with silver nanoparticles, and with increasing nanoparticle concentration antibacterial properties increase. The antimicrobial properties of the modified samples are stable during the studied period (five days).
Thus, a composition based on silver nanoparticles was successfully developed for the processing of packaging materials for the food industry. It is shown that the packaging material modified with silver nanoparticles has antibacterial properties and suppresses the growth of microorganisms. The use of the developed antimicrobial package will prevent the spoilage of food products, increase the shelf life, reduce losses and ensure the preservation of the quality and safety of food during transportation, storage and sale. ■
* Алматинский технологический университет (Алма-Ата, Казахстан) / Almaty Technological University (Alma-Ata, Kazakhstan).