**4.6 Application of nanocomposites**

They are the nanoscale structures the improve the macro properties of food. Some of the nanocomposites used are silica nano clay and polymer clay nano clay. Silver nano clay have good interactions with other particles and also provides a large surface area to volume ratio, enhanced bacterial activity control, whereas polymer nano clay provide more strength and stiffness, smaller cell size, and is a flame retardant.

Polymer nano clay has recently emerged due to its wide-ranging properties such as providing mechanical strength, less shocking treatments, etc. The properties of biopolymer-based coatings were shown to act as hurdles for gas and solutes thereby increasing the shelf life of produce. But they showed poor performance in mechanical resistance and water vapor exchange. To achieve these characters hybrid materials were developed consisting of bio-based polymer and layered silicates such as montmorillonite (MMT). These exhibited great and good results in the chemical, physical and physiological aspects of the product in comparison to the pure one [27].

Nanocomposite constituents are composed of a nanoscale structure that enhances the macroscopic properties of food products. Polymer clay nano clay and silica nanocomposites of nanosilver are the two common nanocomposites utilized in the food packaging industry. Increased stiffness, strength, nucleating agent in foams, smaller cell size, higher cell density, and flame retardant are the impacts of nano clay in polymers. Nanosilver has great antibacterial characteristics which are made out of de-ionized water suspended in silver. Silver nanoparticles have a large surface area relative to volume, so, they interact well with other particles, increasing their antibacterial efficiency. As a result, they are widely utilized in the food


#### **Table 4.**

*Properties of some biodegradable plastics [26].*

packaging business. Although the application of nanotechnology in the food industry was initiated later than other industries, many nanoscientists and technologists have recognized the immense potential of food nanotechnology, particularly in the areas of increasing food quality and ensuring food safety [4].

Polymer/clay nanocomposites are one of the potential applications of nanotechnology in food packaging; they have recently emerged due to their capacity for improving mechanical, barrier, and chemical properties of packaging materials with a small amount of nano clays reinforcement (less than 5% by weight). However major work done on clay polymers concentrated on synthetic polymers majorly. Biopolymers act as a hurdle to solute and gas thereby enhancing the shelf life of produce However, due to their hydrophilic qualities, these films do not retain good mechanical and water vapor barrier capabilities. To overcome these issues, an innovative approach has been developed, by using hybrid materials consisting of polymers and layered silicates such as montmorillonite (MMT) clay mineral, result from the stacked arrangement of negatively charged silicate layers and contain a platelet thickness of about 1 nm with a high aspect ratio (ratio of length to thickness) [28]. The layered silicate filled polymer composites exhibit extraordinary enhancement of mechanical, thermal, and physicochemical properties at a low level of filler concentration when compared to pure polymer and conventional micro composites [27].

In specific, these nanocomposites offer good barrier characteristics, because, the presence of clay layers inhibits the diffusing molecule pathway due to tortuosity [29, 30]. Some of the works done with biopolymer-based nanocomposites were based on starch or polysaccharides, such as chitosan [31, 32], thermoplastic starch and wheat and maize starch. A few studies on protein-based nanocomposites have been available, including whey protein soy protein [31], and wheat gluten. Nanocomposites along with biopolymers exhibited a greater impact when compared nanocomposites alone. The most popular biopolymer is whey protein that has gained popularity due to its transparent coating and effective oxygen barrier. Unlike chitosan film, whey protein films have not shown any antimicrobial activity; therefore, incorporation of antimicrobial agents, such as lysozyme, sorbic acid, and p-aminobenzoic acid and is desirable to induce this feature. Rhim et al., reported that cloister 30R and some chitosan-based nanocomposites showed action against gram-positive bacteria.

#### **4.7 Smart or intelligent packaging**

It is of two types: the one which incorporates integrated circuits and the one that does not (chipless smart packing). The type of packing that includes diagnostic indicators also falls under this umbrella. They can be used for some functions such as humidity, light, heat, mechanical shock, biological agents such as bacteria or viruses as they come in contact.

The conventional packing material use Is limited to only some fresh produce and it can not come up with tolerating the high rates of respiration of fresh produce, however, some breathable polymer films were in use for cut vegetables and fruits. Packing films with acrylic side chains is more beneficial as the side chains melt which results in increased gas permeability and also ensures proper carbon dioxide to oxygen ratio that usually varies with the product. In this way, packing becomes smart as the concentrations of gasses are controlled automatically around the product during storage and transportation and provide the products with high quality to the consumers.

Intelligent packaging technique indicates the freshness of produce by changing colors, so the consumer can know its quality and can check it if any deterioration occurred during the transit. Time-temperature integrators (TTI's) are instruments

#### *Advances in Postharvest Packaging Systems of Fruits and Vegetable DOI: http://dx.doi.org/10.5772/intechopen.101124*

that display irreversible changes in characters such as shape or color. They work based on different principles such as physical, chemical, and biological. The first two types are based on the response towards time, temperature, melting, polymerization, etc… The latter depends on the activity of biological organisms.

Fresh-Check®Life Lines integrator is available as self-adhesive labels, that are attached to the packing material of perishable produce to assure the quality of products to customers. It is based on the principle of color change, which is due to a polymer that has diacetylene monomeric units. It includes a small ring of polymer surrounded by another ring for color reference, the rate of change of color depends on the rate of food quality loss. The color changes from light to dark as the temperature increases.

Vitsab® indicator is based on enzymatic reactions. It has two compartments, one for enzyme plus a dye and the other for substrate (primarily triglycerides). It consists of a bubble-like dot and it is activated by applying pressure, which results in the compartments getting mixed. Because of the reaction between enzyme and substrate, there will be a change in pH and also a change in color. Initially, the dot is in green color and slowly changes to yellow as the product reaches the end of shelf life. The reaction is irreversible and the rate of reaction is directly proportional to


**Table 5.** *Packaging materials and methods effect on the shelf life of fruits and vegetables.*

#### *Postharvest Technology - Recent Advances, New Perspectives and Applications*

the temperature. Single dot tags are used at consumer level packing for monitoring pallets and cartoons. *ripeSense* is the world's first intelligent ripeness indicator.

The Institute of Food Technologists in the United States has defined shelf life as "The period between the manufacture and the retail purchase of a food product, during which time the product is in a state of satisfactory quality in terms of nutritional value, taste, texture, and appearance". Various factors affecting shelf life are product characteristics, which include intrinsic factors, such as water activity, pH, microflora, availability of oxygen, reduction potential; and extrinsic factors, such as temperature, rainfall, humidity, light, etc., enzymic reactions, chemical reactions, and non-enzymic reactions (**Table 5**).

There are various chemical, biochemical and physical reactions that lead to food quality deterioration. These include enzymic and non-enzymic browning, fat oxidation, hydrolysis, lipolysis, and proteolysis that change the physical and chemical composition of food [33].
