A Way Forward With Nano-Antimicrobials as Food Safety and Preservation Concern A Look at the Ongoing Trends

Introduction

Microbial contamination is the recent challenge encountered by food industries from a preservation perspective and has attracted much attention by economists, policymakers, and food researchers too (Baranwal et al., 2018). Despite recent technological advancement, many validations to date are still lying in infancy stages, hence the need to explore more at a fast pace. Presently available conventional methods to avert these issues are not sufficient enough; therefore, better enhancement with upgraded technologies is continuously in need to exploit and secure humankind’s food availability and preservation as well (Bajpai et al., 2018). Nanotechnology is the field that involves the control and application of technology at the nanoscale. These nanomaterials behave as a whole to carry out all the functioning for what we want to exploit; hence, nanomaterial almost resembles similar a big molecule (Baranwal et al., 2018). A wide variety of materials exist today that considered as nanostructured materials (NSMs), but the term NSM validates only those materials which belong to a 1- to 100- nm range. NSMs may exhibit large particle size (>100 nm) when they combine with other materials (like polymers, biomolecules) to form composite NSMs. The classification of NSMs is divided into three categories, which are also separated into subcategories. Three main categories are inorganic NSMs, organic NSMs, and nanocomposites (Dastjerdi and Montazer, 2010). Biochemical mechanisms are involved in the degradation of microbial enzymes, alterations in cytoplasmic membranes of bacteria, and changes in membrane integrity due to the release of metal ions which cause antimicrobial activities. Metal nanoparticles (NPs) differentiate then- response to the bacterial species based on the presence of the peptidoglycan layer. The passage of NPs into cell structures is generally divided into two types—open or non-specific transport and specific transport (Chudobova et al., 2015). Problems in antimicrobials are always noticed with less stability and fast degradability. The encapsulation of food antimicrobials agents with nanocarriers systems increases the high surface area-to-volume ratio and results in the increment of the concentration of antimicrobials at the specific site of the occurrence of microorganisms and allows them to reach at the target site without getting depleted (Blanco-Padilla et al., 2014).

Classification of NSMs

NSM shave widespread domains for the types of nanomaterials and different synthetics pathways that followed to provide an antimicrobial effect at the nanoscale (Bhushan, 2010). They are also showing a huge variation in their shapes and structures, such as crystals, wire, sheets, and capsules. NSMs are mainly classified into three major categories (Figure 5.1). Inorganic NSMs include different categories for the material used and various forms, and some of them have sub-categories too. Nanocrystals are showing the proper alignment of atoms in the single or polycrystalline configuration in one dimension (<100 nm). Nanowires are wire-like structures, having a diameter of few nanometres, and nanoshells are the type of NPs that have spherical shapes with a dielectric core, which is covered by the thin metallic shell. Tw o sub-categories of NPs are metal and metal oxide NPs with a dimension of less than 100 nm. Carbon nanotubes and quantum dots have specific cylindrical carbon structures and semiconducting properties, respectively. Organic NSMs consist of

FIGURE 5.1 (a) Classification of advanced food packaging in food industry; (b) classification of nanomaterials in three categories (left) and structure of some nanomaterials (right) (Barnwal et al., 2016).

four different types—nano/microcapsules, dendrimers, polymeric NPs, and liposomes. These are composed of more complex three-dimensional structures in comparison to inorganic NSMs. The last major category is of nanocomposites, which are divided into organic and inorganic composites (Dastjerdi and Montazer, 2010).

Current Scenario and Ongoing Trends

Many of the NSMs described earlier have importance in various sectors like agricultural and industrial processes, food preservation, water treatment, antibiotics development, and consumer products (mentioned in Table 5.1). Mechanisms followed by them mostly have common targets that affecting cell membrane by the release of metal ion of Ag+ and Au+ in metal oxide NPs. In some cases, carbon-based structures in nanotubes, graphene, and fullerene cause the generation of reactive oxygen species (ROS) and produce reactive nascent oxygen (Dakal et al., 2016). Although in some different nanoscale materials, the mechanism of antimicrobial activity and how the cell wall is changing in its integrity are still not clear (Kong et ah, 2016). In addition to the taking part directly in the mechanism, a few organic NSMs are used as carriers of inorganic NPs and antimicrobials to provide encapsulation to them for delivering efficiently to their respected targets.

TABLE 5.1

Different Nanostructured Materials (NSMs) and Their Dimensions, Targeted Microbial Strains, Effects, and Applications