Nano-Starch Films as Effective Antimicrobial Packaging Materials

Introduction

Packaging materials are those that provide protection, communication, containment, and convenience to food products while maintaining their safety and quality during the period of their storage and transportation. A decent food package has the ability to extend the shelf life of food products by preventing them from spoilage, chemical contamination, moisture, oxygen, and external force. In past 20 years, the food-pack- aging industry, plastic has been used as a packaging material, which increases the problem of the waste disposal. So, recently, the food-packaging industry has grown its interest in the biodegradable and antimicrobial packaging for food products. Nowadays, nanotechnology is advanced field to fight against several problems like packaging, medicine, formulations, and cosmetics (Nakazato et ah, 2017; dos Santos Caetano et ah, 2018). Several food ingredients are used for the preparation of nanoparticles (NPs), such as protein, lipids, surfactants, minerals, and polysaccharides (Chang and McClements, 2014; Agarwal et ah, 2020; Dhull et ah, 2020). The physico-chemical, releasing, protective, and encapsulation properties affect the composition of nanoparticles (McClements and Yan, 2010). To overcome this problem, new techniques such as nanoemulsion, nanospheres, nanocapsules, nanoliposomes, and nanofibers are being used for the production of packaging material in food industries, as shown in Figure 19.1.

Nano-sized starch particles have gained much attention due to their unique properties from bulk material. Starch is a naturally existing biopolymer that is extracted from plants in the form of small-sized granules. Starch is composed of amylose and amylopectin units linked by a (1-4) and a (1-6) (Punia et ah, 2019). The amount of starch depends on the type of source (Punia et ah, 2019). Starch is a source of energy that is obtained from the carbohydrates (Zhao et ah, 2018; Punia et ah, 2020). Starch NPs are also known as nanocrystals, but they differ in their structure. Nanocrystals include a crystalline structure whereas NPs include an amorphous region (Yang et ah, 2018). They both show effective properties in different areas such as food

New technology used for the preparations of packaging material

FIGURE 19.1 New technology used for the preparations of packaging material.

additives, coating binder, flavor binders, pigment carrier, vitamins, and emulsion stability (Ahmad et al„ 2019). Nano-starch-based packaging film is used more nowadays due to the its biocompatible, biodegradable material, edibility, sustainability, and low cost (BeMiller, 2018). It is prepared with the blend of non-starch biopolymers such as chitosan (Bonilla et ah, 2013), gelatin, and carboxymethyl cellulose (Ghanbarzadeh et ah, 2011). The starch matrix is also filled with starch nanocrystals, cellulose nanocrystals (Ali et ah, 2018), montmorillonites (Li et ah, 2018), metal NPs (zinc oxide [ZnO] and silver [Ag] NPs; Nafchi et ah, 2012), lysozyme (Fabra et ah, 2014), and antimicrobial compounds such as potassium sorbate (Shen et ah,

2010). Several commercial starches are available for the preparation of films, such as Mater BiO, Bioplast (Kaur et ah, 2018). Biopar, Cereplast, Biostarch, Ever CornTM, and Terraloy TM (Hafsa et ah, 2016).

Synthesis Process of Nano-Starch

Nano-starch can be synthesized by variety of methods such as acid hydrolysis, regeneration (LeCorre and Bra, 2012), and enzymatic treatment (Le Corre and Helene, 2014); physical, mechanical, and thermal treatments include nanoprecipitation, high- pressure homogenization, ultrasonication, gamma irradiation, and reactive extrusion, among others (Kim et ah, 2015; Liu et ah, 2016).

19.2.1 High-Pressure Homogenization

In this process, liquid is passed through microfabricated channels by external pressure, such as electro-kinetic mechanisms or micropumps (Hale and Mitchell, 2001). Due to the high shearing in the product responsible to speed up the velocity using an electronic hydraulic pump, (Banderas et ah, 2005), the size of the particles is reduced through the shear force due to breakage of hydrogen bonds (Liu et ah, 2016). Highspeed techniques (ultrasonication) also help in the degradation of the crystalline structure (Ding and Kan, 2017).

19.2.2 Extrusion Technique

Higher temperatures, pressure, and shear forces are responsible for the structural change with change in melting point, fragmentation, and gelatinization (Song et ah,

  • 2011). In this process, the amount of water is minimal, which affects the gelatinization process. The higher shear force affects the structure of the starch granules due an interruption in the molecular bonds (Ding and Kan, 2017).
  • 19.2.3 Acid Hydrolysis

This process used for the preparation of starch nanocrystals which are isolated from the sulfuric and hydrochloric acid of amorphous regions. The size of the granules is dependent on the lower temperature as compared to the gelatinization temperature, which responsible for the crystals that are not soluble in the water (Wang et al.,

  • 2014). After the process, the residues left are highly crystalline and platelet-like in structure with a nano-size which can be stable at the higher temperatures during food processing (Aldao et al., 2018).
  • 19.2.4 Enzymatic Hydrolysis

It is the pretreatment whereby the rate of hydrolysis is increased in native starch granules before the acid hydrolysis. For this process, various enzymes are used, such as glucoamylase, (3-amylase, pullulanase, and a-amylase, to reduce the time of acid hydrolysis (LeCorre et al„ 2012). These enzymes affect the structure of starch granules, which make the amorphous region more hydrolysable and selectively. Enzymes like glucoamylase treated with starch are helpful in decreasing the acid hydrolysis time from 5 days to 45 hours (Kim and Lim, 2008). However, this process is more effective compared to acid hydrolysis because it reduces the time, increases the yield to about 55%, and uses no chemical reagents (Sun et al., 2014).

19.2.5 Ultrasonication

This is the advance technology for the processing of food due to the low-energy consumption and short processing time (Kim et al., 2015). In this process, ultrasonic cavitation was used to generate microbubbles when the high energy is released. It helps degrade the polymer due to the higher temperature and high pressure. It also disturbs the surface of the starch, which reduces the crystals of the NPs with an increase in the amorphous state. Ultrasonication also affected the production of NPs and hydrolysis efficiency, and the NPs’ size varied between 30 and 200 nm (Amini and Seyed, 2016).

19.2.6 Gamma Irradiation

Polymers are modified through cross-linking, degradation, and grafting with the use gamma irradiation, which help in the reduction of the starch size (Akhavan and Ataeevarjovi, 2012; Punia et al., 2020). In study by Singh et al. (2011), larger molecules of the starch reportedly were converted into the smaller molecules in the amorphous state, and the physical properties and structure of the starch were affected. This method is similar with the acid hydrolysis process, whereby the active free radicals are generated which reduce the hydrolysis of starch (Lin et al., 2011).

 
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