Plant extract mediated silver nanoparticles and their applications as antimicrobials and in sustainable food packaging: A state-of-the-art review

Background: Nanotechnology is an emerging, novel area of applications in antimicrobial and eco-friendly food packaging that have tremendous potential benefits. Silver nanoparticles (AgNPs) have been extensively studied and frequently used in food packaging applications due to their superior physicochemical, biological and antimicrobial properties. Scope and approach: Recently, plant extract-mediated synthesis of AgNPs has gained enormous popularity due to environment-friendliness, relatively economical synthesis, and effective functionality in food packaging applications. Numerous medicinal plant extract(s) are used in the synthesis of AgNPs, which are most commonly spherical in shape and within 2-80 nm range in size. Amount and composition of plant extract, metal ion concentration, reaction temperature and time, and pH of the reaction mixture are the key factors affecting shape, size, morphology and crystallinity of the synthesized AgNPs. Key findings and conclusions: Compared to other synthesis methods, including microbial synthesis, plantmediated synthesis of AgNPs is faster, more convenient, and can be effective in utilization of wastes generated by fruit and vegetable producers and handlers. Plant-mediated AgNPs are effective against both Grampositive and Gram-negative foodborne pathogens and spoilage bacteria. Silver (Ag+) ions of AgNPs bind with negatively charged functional groups present in the microbial cell membrane, thereby increase permeability of the membrane disturbing the cellular transport system leading to cell death. In addition, entry of Ag+ ions into the cell cytoplasm may damage DNA, RNA, peptide forming compounds and metabolic enzymes resulting in the inhibition or hampering of cell division and microbial respiration. Scientific efforts are being made on the application of plant-mediated AgNPs in bionanocomposite films and coatings, as effective food preservation strategies. This review highlights innovative applications of plant-mediated AgNPs in sustainable antimicrobial food packaging.