Introduction

Food is one of the basic human needs. Foods derived from plants and animals contain essential nutrients such as moisture, carbohydrates, proteins, fats, minerals, vitamins, and other non-nutrients.¹ Food items get spoiled due to biological, chemical, environmental or physical factors. Among them, the biological (caused by microorganisms) and environmental factors including temperature, moisture, oxygen, and light can cause several undesirable changes in the food that leads to either rejection or riskiness to consumers.² The major sustainable development goal of the United States is to eradicate hunger and to feed 10 billion global populations by 2050. Further, it create trade-offs between food security, sustainability, food safety, and food produced.³ A reliable food supply with an emphasis on food deterioration, storage, and transport is necessary to accomplish the goal.⁴ Food spoilage may alter the nutritional values, flavor, colour, texture, and palatability of the product.¹ Hence, foods need to be preserved from spoilage to maintain their quality for a prolonged period.

Food preservation refers to the process or method applied to control both internal and external factors which may cause deterioration of food. Therefore, food preservation plays an important role in extending the shelf life and retaining food quality and food safety.² This is achieved by controlling enzymatic activity, certain chemical compounds in food, and spoilage microorganisms.⁵

Preservation is usually associated with various food processing steps to attain a desirable food quality and nutritional value. Food preservation methods include but are not limited to refrigeration, freezing, canning, drying and dehydration, packaging, smoking, application of food additives, modified or controlled atmospheric storage, and irradiation.² In spite of the scientific advances in preservation technologies, several food items still depend on conventional methods for storage such as dehydration, low temperature, osmosis, wood smoking, or organic chemicals.⁶ Nevertheless, some novel food processing and preservation techniques are developed to enhance the shelf life of several foodstuffs. Emerging non-thermal food processing technologies includes cold plasma, ohmic heating, high pressure, pulsed electric field, and ultraviolet irradiation.⁷

Among the several food preservation techniques, packaging plays a crucial role in every stage of the food industry also in the preservation and storage of food products during the entire supply chain. Recently, food packaging has received great attention as it offers high-quality food with an extended shelf life to consumers. As a result, innovations were done in smart packaging which would possess active compounds, excellent barrier properties, and biodegradability to reduce environmental pollution.⁸ Currently, the application of nanomaterials in food packaging is found to be a promising area to enhance the functionality of packaging material.⁹

Nanotechnology deals with the production, manipulation, and evaluation of materials at the nano size ranging between 1-100 nm. When the size of the particle is reduced to the nano level, it exhibits significantly different chemical properties than in its macrosize.¹⁰ Numerous food components are used for the development of nanoparticles which include carbohydrates particularly starch, cellulose etc. protein, lipids, minerals, and surfactants.^11,12 These nanomaterials present an excellent advantage in terms of biodegradability and biocompatibility in food packaging applications.^13,14 The composition of the nanoparticles is altered by their physicochemical, protecting, releasing, and encapsulating capabilities.^14,15 To address this drawback, new methods including nanocapsules, nanoemulsions, nanospheres, nanofibers and nanoliposomes are developed to prepare food packaging material in the food industry.¹⁶ Rice starch and potato starch nanocrystals prepared by acid hydrolysis (3.16M sulfuric acid) were used in the starch-based films. Application of starch nanocrystals in the films has reduced water vapor permeability, increased crystallinity, reduced the surface roughness, and fracture.¹⁷ However, food packaging using nanomaterials remains the most under-exploited area of research in the field of food science and nanotechnology.¹⁰ This review incorporated the literature on starch-based bio-nanocomposites, enabling the creation of new frameworks and perspectives on nanostarch packaging systems. Hence the present review prudently compiles information about the functions of packaging, sources of starch, methods for the synthesis of nanostarch, characterization of nanostarch, and regulatory aspects of nanomaterials in packaging.

Functions of food packaging

Food packaging is viewed as a marketing tool for food products in the industry, and it also aids in grabbing consumers’ attention.^18,19 The main purpose of food packaging is to communicate information, containment, protection, ease of handling, and facilitation of handling (Figure 1). The protective function includes mechanical protection, barriers (against oxygen or water vapour), thermal, and sealing properties. The ‘facilitate handling’ function includes features such as unitization, apportionment, resealability, and emptying. Communication functions consist mostly of product and packaging information and instructions, as in how to properly store, open, and dispose of the package. Moreover, instructions for extending the shelf life of packaged food’s by encouraging consumers to freeze leftovers may be included on the packaging.^14,20,21 Secondary functions of packaging include convenience, freshness indication, damage indication, and traceability. Traditional packaging such as gunny bags, glass jars, courier bags, cardboard, bubble envelopes, cartons, etc. are typically applied for a finished product.²²

Figure 1: Functions of food packaging Click here to view Figure

Different types of packaging include:

Primary packaging

Secondary packaging

Tertiary packaging

Primary packaging

It is the packaging material which is in direct contact with the food items. It encloses, holds and protects the food from the external environment. It is the smallest system of distribution. The form, dimensions, and consistency of the product determine the main priorities for primary packaging. Depending on the product, transit, and storage conditions, primary packaging can serve diverse applications and functions. The most evident and crucial function is to protect and preserve the product from external damage, contamination, spoilage, and chemical imbalances. Moreover, primary packaging keeps a product in storage, often for longer periods.

Example: Chips packet

Secondary packaging

It is the material that lies exterior to primary packaging and helps to group the primary packages together and further protect and label the food product. The two primary purposes of secondary packaging are branding and display and logistics. Secondary packaging is essential in marketing the product. When it comes to displaying packing, this is extremely important. It makes handling, transporting, and storing several products easier. Secondary packaging is intended to protect not only the product but also the primary packaging, which often is the packaging most visible to the consumer in retail displays

Example: Paperboard cartons of cornflakes, shrink wrapped bundles etc.,

Tertiary packaging

Tertiary packaging material usually holds the secondary packages which facilitate handling bulk packaging, transportation, distribution, or storage. It not only protects the product but also the primary and secondary packaging. It serves three different functions

Protection: The primary purpose of tertiary packaging is to safeguard the product while it is being transported. Given the nature of the road and rail infrastructure, tertiary packaging should be made to withstand natural disasters like humidity, extreme heat, and severe weather, as well as unintentional shocks, impacts, and accidents of any kind.

Versatility: While designing tertiary packaging, keep in mind that there may be several stages in transit before the product reaches its final location. Multiple off-loading, re-packaging, re-loading, and even product storage are included in this.

Customized solutions: Tertiary packaging should be as unique as the product itself and have the same size, shape, and consistency as the product. The emphasis in this case is on the packaging that is as compact, durable, and that takes up as little space as possible.

Examples: Brown cardboard boxes, wood pallets etc. 

Figure 2. An illustration showing the functions of food packaging and their environmental impact Click here to view Figure

The major functions of packaging ^14,21,22 (illustrated in Figure 2) are listed below:

The basic function of food packaging is to protect the food from external factors such as the environment which include humidity, sunlight, water vapour, oxygen, heat, or physical damage during transportation, distribution, and storage.

It also aids in preserving the food in its original state and provides information about the nutritional and ingredients information.

Indication of tampering, freshness, shelf life, and traceability is other functions of packaging.

It supports marketing of the product by providing the identity and ensures that it adapt to the specifications, laws, and regulation of the governing body.

It enhances the shelf life of the food products

It offers the consumer convenience in handling the product

Environmental impact of food packaging

Food packaging is made up of several materials which may include plastic, laminates, coated sheets, films, paper, metals etc. These materials decompose at different rates while some of them undergo minimum degradation.  Some materials like plastic when discarded affect the environment and seriously damage the ecosystem as they are made up of polyethylene, polystyrene, and polyvinyl chloride. Hence, they are considered a hazard to the environment.^14,23 Packaging material such as wood and paper are obtained from forest resources and the production of these material releases toxic gasses into the atmosphere. These toxic gases are not only harmful to humans but also to other animals.  Non-degradable packaging systems when disposed of remain for a prolonged period abolish soil components which directly affect the agriculture productivity. Further, these consequences will result in food insecurity. Packaging waste as dumped on land would become a threat to animal life while disposed within the ocean will demine aquatic life.^23,24

Litter

Litter is usually associated with packaging material and is a part of total waste yet is a matter of concern because of its hazardous effect on human, animal, and marine life. The constituents of packaging substances including plastic bottles, glass, paper cups, and plastic wrappings are the major components of litter. Litter of plastic origin is the chief concern for an aquatic environment. It generates from land and sea sources, and the debris such as fishing gear including nylon buoys, lines, and nets; synthetic ropes, packaging bands, starps, and general litter, such as plastic sheeting, bags, and bootless.^25,26 Few studies have reported a positive correlation between plastic debris and the bioaccumulation of hazardous chemicals, a presentation that the concentrations of polychlorinated biphenyls (PCBs) and trace metals in seabirds and higher brominated polybrominated diphenyl ethers (PBDEs) were positively related with plastic debris.²⁷

Water pollution

Water pollution is originated by discharging the sludge obtained during the manufacturing of packaging substances. The major cause of water pollution is paper production as its waste effluent releases biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids, and volatile suspended solids (VSS). Moreover, the manufacturing of other packaging materials which include dye, coatings, and adhesives causes hydrocarbon pollution. While discharging thermoelectric cooling water leads to thermal pollution and accidental emissions particularly fire accidents during production or processing activities are also a matter of concern.^26,28 Landfill leachates cause water pollution, which are the product remnants of the packaging materials. Historical packaging can also be the source of organic plasticizers for PVC, or lead and cadmium from pigments.²⁹

Air pollution

Food packaging manufacturing is also one of the factors for air pollution. The components released during fire accidents at the workplace or incineration activities for waste disposal which include chlorofluorocarbons, vinyl chloride, and hexane pollute the environment. Dumping packaging waste at landfill sites undergoes decomposition and releases CO₂ and methane. Carbon dioxide is also released during the production of glass and steel for packaging applications. In addition, emissions corresponding to electricity generation and transportation are also part of environmental pollution.^26,28 In addition, packaging-related sources of air pollution from electricity generation (CO₂,SO₂, and NO_x emissions) and logistics-related emissions including CO₂,SO₂, NO_x, hydrocarbons, and dust. The need of accounting for emissions associated with transportation is rising, especially when reuse or recovery is being considered.²⁹

Solid waste

Solid waste is generated during the extraction and processing of raw material for packaging material which will be directed to landfill sites. Solid waste is categorized as pre-consumer and post-consumer solid waste. In general, pre-consumer waste produced from the industry is recycled while non-recyclable waste is discarded. Whereas, post-consumer solid waste needs more attention to recycle the materials however, not all collected materials are recycled as few products made from recycled waste will sooner be waste again. Hence, incineration of post-consumer packaging waste can reduce a volume reduction of about 20 to 40 %.^26,28

Synthetic food packaging materials of petroleum origin and their constitutent materials are non-degradable and have become a severe environmental concerns. Synthetic materials such as low-density polyethylene (LDPE), polyester, polyvinylchloride, and high-density polyethylene (HDPE) materials are most commonly used in the packaging industry.^30,31 Hence these materials are restricted for packaging applications and researchers are working on an eco-friendly alternative natural polymer. Starch is found to be one of the most promising natural polymers for developing sustainable material due to its biodegradability, renewability, and low cost.³²

Starch sources, production statistics, and nanostarch

Starch is a most abundant natural biological macromolecule which has great industrial applications. It is a renewable and biodegradable storage polysaccharide in plants. The chemical formula of starch is (C₆H₁₀O₅)_n. Starch is composed of two polymeric components named amylose and amylopectins. Amylose is a low molecular weight and long-chain linear polysaccharide of glucose linked by α-1,4 glycosidic bonds while amylopectin is a short and highly branched polymer linked by both α-1,4 glycosidic and α-1,6 glycosidic bonds.^33,34. Amylose (20-30%) and amylopectin (70-80%) content of the starch varies according to the source from which they are extracted.³⁵ The amylose and amylopectin molecules in the starch are arranged as crystalline clusters of double helical structure, forming stacks of alternative crystalline and amorphous lamella. The size (0.5- 175μm), shape and structural arrangement of the starch granules usually depend on the plant genotype, cultural practices, and environmental interactions.³⁶ The major source of starch includes corn, tapioca, potato, wheat, and sweet potato for industrial applications, whereas rice, sorghum, barley etc. are used as a minor source of starch around the globe. In addition, starch is also commercially isolated from rice, arrowroots, mung bean, and sago (Figure 3).³⁷ Corn starch is in high demand because of its textural properties, especially as a thickening agent in industries such as dairy and beverages.

Figure 3: Different sources of commercial starches Click here to view Figure

According to the global industrial starch market report (2020-2028), the market value of starch for the year 2020 was USD 97.85 billion and is expected to be increased by 7% between 2020 and 2028. Global production of starch has been estimated between 88.1 and 97.7 million tons in 2020. Corn starch accounts for 75% of this amount, followed by cassava (14%), wheat (7%), and potato starches (4%).^38.39 These statistics indicate that there is a great interest in exploring new starch sources for industrial applications.

It is among the important polymers that find a wide application in food industries as a thickening agent, bulking agent, preservative, stabilizer, fat replacer, and quality improver in bakery products, extruded products, dairy products, confectioneries, soups, noodles, mayonnaises etc.⁴⁰ The diverse applications of starch are influenced by their physicochemical, functional, thermal properties. However, starch in its native form has limited applications and hence they are subjected to modifications for versatile use.⁴¹ One such industrial application which received profound interest is starch-based biodegradable food packaging which reduces environmental pollution.⁴²

Starch is an ideal material to produce nanoparticles or nanocrystals as it is a biodegradable natural polymer. In recent times, starch-based nanomaterials gained focus because of their unique properties, and biodegradable nature.⁴³ Starch-based nanomaterials are produced by various techniques including physical, chemicals, and enzymatic methods, and would be employed as a sensor for quality indication in food products, and reinforcement biodegradable or nonbiodegradable polymeric matrix.⁴⁴ Starch-based nanosystems are classified into two types based on their crystallinity as starch nanocrystals and starch nanoparticles. Starch nanocrystals are produced from disorganized semi-crystalline starch granules when heated below their  gelatinization temperature. Starch nanocrystals are produced commonly by acid hydrolysis and have wide application in food as nanofiller for reinforcement of nanocomposites ^45,46 emulsion stabilizers.^47,48

While starch nanoparticles are nanosized amorphous starch granules with crystallinity of less than 10%. They are used as a carrier systems for drug delivery. Starch nanoparticles are prepared by using several methods such as ultrasonication, nanoprecipitation, high-pressure homogenization etc. ^14,49 Starch-based nanosystem offers numerous benefits including lower viscosity, greater surface area, and better delivery efficiency of active compounds.^50,51 Starch-based nanosystems have been developed from various botanical sources such as potato starch,^52,53 cassava starch,⁵⁴ banana starch,⁵⁵ corn starch,⁵⁶ wheat starch,⁵⁷ chestnut starch,⁵⁸ lotus seed starch.⁵⁹ Application of nanosized (1-100 nm) organic or inorganic particles to starch-based thermoplastics offers a contemporary and extraordinary packaging technology, which is known as nano-inforced packaging material.³¹ This type of packaging material provides good flexibility, biodegradability, and less molecular mass. In addition, its tensile strength is similar to low-density polyethylene (LDPE). Moreover, these types of nano-packaging systems are demonstrated to act as a barrier against moisture, oxygen, and microorganisms.^31,60

Techniques for the synthesis of starch nanocrystals

Starch nanocrystals can be developed by different methods including acid hydrolysis, enzymatic hydrolysis, ultrasound treatment, and a combination of these methods.^61,62,63 (Table 1). Several factors affect the yield, morphology, and properties of starch nanocrystals and further their industrial applications. Based on the literature, the yield of the starch nanocrystals is mainly influenced by the amylose content and the hydrolysis conditions whereas the size of the nanocrystal depends on the botanical source of the starch granules, degree of crystallinity, and their amylose levels.^61,64,65

Acid hydrolysis

Acid hydrolysis is the most predominant method used for the synthesis of starch nanocrystals. In general, starches are subjected to a two-stage hydrolysis reaction: the first stage is characterized by rapid hydrolysis where the amorphous regions of starch granules are attacked. While the second stage involves a slow hydrolysis reaction in which the crystalline portions get cleaved.^66,67 Few studies reported three stages of reactions involving rapid, slow, and very slow hydrolysis.^68,69

Starch nanocrystals synthesized by this method exhibit a platelet-like shape with a high degree of crystallinity. During the synthesis process, starch is mixed with a dilute acid such as sulfuric acid, hydrochloric acid, or oxalic acid with constant agitation under controlled temperature for an extended period (a few seconds to days). Later, the nanocrystals formed by acid hydrolysis are centrifuged and washed with distilled water for neutralization of the eluent. Lastly, the suspension is mechanical stirring to obtain a homogenous suspension.⁷⁰ Rice and potato starch nanocrystals were prepared by acid hydrolysis using 3.16 M H₂SO₄ (sulfuric acid) for 5 and 7 days. The rice starch nanocrystal presented a particle size ranging from 300 to 532 nm while the potato starch nanocrystal produced by this method showed a particle size of 548-987 nm.⁶¹ In a similar study, Velásquez-Castillo et al.⁶⁵ developed nanocrystals from quinoa and waxy maize starch with sizes ranging between 400 and 900 nm. In this study, acid hydrolysis was conducted in two stages, particle size of the starches was found to be 100 nm and 400-900 nm in the first and second phases respectively. As per Singh et al.⁷¹ acid hydrolysis breaks the starch granules and produces starch nanocrystals with particle sizes 100-fold smaller than the native starch. Zhou et al.⁷² demonstrated the nanocrystal synthesis from waxy maize using oxalic acid. In another study, after an acid-treatment process using sulfuric acid, the wheat starch granules were destroyed and degraded to nanoparticles with a size range of 30–80 nm.⁷³ Rice starch (300nm) and potato starch (548nm) nanocrystals were prepared by acid hydrolysis (3.16M sulfuric acid) for 5 to 7 days.¹⁷

Enzymatic hydrolysis

Enzymatic hydrolysis is a seldom adopted method for nanocrystal synthesis from starch granules. Several enzymes are employed in the enzymatic synthesis of nanocrystals including α-amylase, β-amylase, pullulanase, and glucoamylase.⁵² These enzymes target the starch granule structure which converts the amorphous region to more resistant to selective hydrolysis. Enzyme hydrolysis is also used as a pre-treatment method prior to acid hydrolysis. Pre-treatment of starch using glucoamylase reduces the duration of acid hydrolysis from 5 days to 45 hours.⁷⁴ This method is more advantageous over acid treatment as it reduces the reaction time, and increases the yield up to 55%.⁷⁵ In a recent study, nanocrystals (100-300 nm) were generated from maize, potato, and cassava starch by application of α-amylase for about 30 min.⁶² Hao et al.⁷⁶ demonstrated the enzymatic pre-treatment (glucoamylase) of waxy potato starch prior to acid hydrolysis. The results presented a starch nanocrystal with a particle size of 80 nm. Waxy maize starch nanoparticles prepared by enzymatic treatment using pullulanase showed globular shapes with diameters of approximately 5–25 nm.⁷³

Ultrasonication                                

Ultrasound treatment is an advanced method of processing food materials because of the low-energy consumption and less processing time.⁶⁷ Ultrasound works by cavitation phenomena during which microbubbles were generates when an ultrasound wave is introduced into the sample. It also disrupts the starch granule structure and creates pores on the surface that might act as channels for acid or enzymatic hydrolysis.^77,78 Sonication would affect the yield of nanocrystals, hydrolysis efficiency, and size which varies from 30 to 200 nm.⁷⁹ The production of starch nanocrystals using ultrasound was inspired by the synthesis of nanofibers from cellulose. Nanofibers were developed from cellulose successfully using ultrasound in several studies.^80,81,82 In a study, Liu et al.⁸³ developed nanocrystals of size 100-200 nm from debranched waxy corn starch treated with ultrasound for 5-10 min. Ultrasound-assisted acid hydrolysis was studied by Hakke et al.⁶³ for the synthesis of maize starch nanocrystals (150nm). The treatment shortened the synthesis time for the formation of starch nanocrystals which is more favorable over conventional acid hydrolysis.

Dual treatments

An effective method to generate starch nanocrystals is to apply dual treatments i.e., pretreatments with ultrasound, ball milling, or enzymatic hydrolysis followed by acid hydrolysis. Coupling of these methods is reported to enhance the efficiency of acid hydrolysis and reduce the treatment time by several folds and further the particle size.^84,85 Hakke et al.⁶³ developed oval platelet-shaped starch nanocrystals by pretreating maize starch with ultrasound (20 kHz for 20 min) followed by acid hydrolysis using 0.25 M sulfuric acid for 50 min at 30 ^oC. The proposed method presented a yield of 36% with an extremely low treatment time of 2 hours (reduced from 48 hours). This ultrasound-assisted hydrolysis produced nanocrystals with a particle size ranging between 50 and 100 nm.⁶³ In a similar study, corn starch when treated with ultrasonication and sulfuric acid generated starch nanocrystals with particle size below 100 nm. The yield of nanostarch was about 21 % and crystallinity was found to be 40%.⁷⁹ Ball milling is a cost-efficient and eco-friendly processing method that has capacity to produce starch properties.^86,87 A combination of ball milling (15-90 min) and acid hydrolysis (3.16M H₂SO₄/ 40^oC/5 days) has produced starch nanocrystals (19.3 %) with a short duration. The nanocrystals are found to be round-edged with an average diameter of 31 nm.⁸⁸ According to Dai et al.⁸⁸ ball milling is observed to be a more economical and efficient pre-treatment method prior to acid hydrolysis for the production of starch nanocrystals when compared to enzymatic pretreatment or ultrasound-assisted hydrolysis. Moreover, ball milling does not require additional purification or specific instruments for mass production. Hao et al.⁸⁵ reported pores and cracks after enzymatic hydrolysis of waxy potato starch that created a pathway for acid penetration to produce nanocrystals (80 nm). The enzymatic pretreatment decreased the acid hydrolysis time.

Table 1: Synthesis of starch nanocrystals using different methods

AH: Acid hydrolysis; AHD: Average hydrodynamic diameter; BM: Ball milling; CL: Cross-linking; D: Diameter; H: Height; US: Ultrasound

Characterization of starch nanocrystals

Globally, research has shown that starch nano-particles can be developed from ultrasound treatment and high-pressure homogenization methods with nano-metric scale sizes and the ability to form films.^70,96,91,97 Also, several techniques have been developed to make starch nanoparticles of small size that possess high efficiency and low cost by reducing starch viscosity in aqueous paste without chemical treatment requirement.^70,97,98

The common methods that have been used to characterize starch nano-starch are Scanning Electron Microscopy (SEM), non-contact Atomic Force Microscopy (nc-AFM), transmission electron microscopy (TEM) and dynamic light scattering (DLS). These techniques have shown the shape and dimensions of the obtained starch nanoparticles from crops such as potato and cassava starch to fit the block lets. TEM and DLS also revealed that starch nanoparticles had narrow size distribution, high dispersibility, and spherical shape.^70,51 It was also discovered that starch nano-particle films from high-pressure homogenized dispersions had lower elongation but higher tensile strength and good moisture barrier capacity and better film transparency.^70,97

Starch nanoparticles (SNPs) have lower nano-metric dimensions in the range of 100 nm which results in better dispersion and compactness of polymeric structure.⁷⁰ Da Silva et al.⁷⁰ also revealed that the insertion of starch nanoparticles in a polymer leads to nano-composite producing great properties better than traditional composites.

The mechanical properties, water vapor permeability (WVP), and biodegradability of composites are improved by adding SNPs.⁷⁰ Compactness of the polymeric structure of nanocomposite films results in a decrease in the WVP making water vapor diffusion more difficult and thereby reducing permeability; however, if the reinforcement is derived from starch nano-crystals from the same material as the matrix like starch nano-crystals dispersed in starch films then better compatibilization may occur.⁷⁰ But the concentration of starch nanoparticle incorporated in a matrix polymeric need to be ascertained as lower nanoparticle concentration could result in better dispersion in the films and reduces permeability. Previous studies^70,99,100 showed that inserting less than 6% concentration of SNPs led to reduced WVP. They further observed that the use of a higher concentration of the SNPs resulted in an increase in WVP. However, this is not feasible for food packaging use because it increases the food degradation rate.⁷⁰ But water vapour permeability values are important for biofilm applications in food packaging. This is because materials that have good permeability to water vapor will be suitable for fresh food packaging and a slightly permeable biofilm will be good for dehydrated food packaging.^70,101

SNPs have been found to increase the process of biodegradation of composites. This is attributed to the fact that water diffuses into the polymer sample in the soil resulting in swelling and biodegradation as a result of an increase in microbial.^70,102 It was found by Costa et al.¹⁰³ that cassava starch nano-crystals (CSN) obtained by acid hydrolysis to strengthen nanocomposite films from the same matrix with 10% CSN showed a larger weight loss due to greater microorganism access.

Starch and other polymer nano-crystal–based food packaging materials

Starch–based nanocomposites

Starch is a natural polysaccharide obtained from plant materials and has been used for bio-based packaging. It is a readily available, cheap, eco-friendly, and biodegradable polymer used for packaging. But its shortcomings such as low mechanical and barrier properties, and sensitivity to UV and moisture affect starch utilization.¹⁰⁴ Starch has been incorporated with nanoparticles like ZnO, TiO₂, Graphene, and poly (methyl methacrylate-co-acrylamide) to improve its mechanical and barrier properties.^105,106 Starch native granules are greatly affected by their sources and this makes them vary from micro to nano range (<100 μm), amorphous and semicrystalline (100–400 nm), amorphous and crystalline (9–10 nm).¹⁰⁷ The mechanical or barrier properties of starch have also been strengthened through chemical modifications such as acetylation and hydroxylation to replace the ester/ether group. ^108,109,110 Rice starch and potato starch nanocrystals prepared by acid hydrolysis (3.16M sulfuric acid) were used in the starch-based films (Table 2). The application of starch nanocrystals in the films has reduced water vapor permeability, increased crystallinity, and reduced the surface roughness and fracture.¹⁷ In another study, reinforcement of waxy maize starch nanocrystals in pea starch film reported an increased tensile strength of the composite film while the moisture content, water vapor permeability, and water-vapor transmission rate of the composite films decreased significantly.¹¹¹ Le Corre et al.¹⁰⁹ used acid hydrolysis of native starch as an reinforcement agent to produce starch nanocrystals.¹¹² Starch-based thermoplastic films have been used as food wrappers as well as for food-containing casing/crates but due to poor strength have been modified chemically or plasticized in order to improve their strength.¹¹²

Table 2: Influence of nanostarch on the properties of bio-composite films/packaging materials

 Chitosan based nanocomposites

Chitosan is an abundant biopolymer which is produced from chitin, a natural polysaccharide by deacetylation of chitin. Chitosan is a biodegradable/ biocompatible polymer with antimicrobial properties.^117,118 Chitosan and chitosan-based systems have been used to produce biocompatible or biodegradable films, coatings, composite materials, and nanocomposites.¹¹⁸ Sriupayo et al.¹¹³ used chitin sources from marine natural sources such as crustacean shells through the process of deproteinization to produce chitin nanoparticles or nanowhiskers. The process involved the use of hot alkaline KOH and then followed by hydrolysis with hot HCl under heavy stirring conditions. Chang et al.¹¹⁸ on the other hand used a double acid treatment procedure involving the repetitive process of sonication and disruption/dispersion. Chitin nanoparticles have also been made by ionotropic gelation of chitosan with sodium tripolyphosphate.¹¹⁹ The properties of chitosan-based packaging materials have been improved by adding micro and nano-reinforcements in a polymer matrix or through the unification of chitin with other materials such as layered nanosilicates. ^{120,121,122.123}

Cellulose-based nanocomposites

Cellulose is an abundant biopolymer and polysaccharide that consists of glucose monomers. Cellulose derivatives like cellulose nano-composites (CNC) are used as fillers to reinforce polymer matrices since native cellulose does not have good packaging qualities.^124,125 The incorporation of CNC improved the mechanical, thermal, and barrier properties of cellulose polymeric matrix.^126,127,128 Other forms of cellulose inserted for nano-reinforcements are nano-fibrillated and cellulose nano-whiskers.¹²⁹ Nanofibrils have a diameter in the range of 2–20 nm and examples of cellulose nano-composites are metal oxides such as Fe₃O₄, TiO₂, and metal nanoparticles like silver, and nanoclay which enhance packaging. Cellulose fibrils consist of amorphous and crystalline regions; the crystalline part is separated resulting in cellulose whiskers. Nano-whiskers are extracted by acid hydrolysis from the amorphous region which keeps the crystalline region unaffected.¹³⁰ Also, packaging films are produced from cellulose from bacteria. Although, it has a similar chemical composition as plant-based cellulose but has different properties and structures, however, it has better mechanical properties, water barrier, crystallinity, and nanofibrillar network and is therefore more preferred over plant cellulose for reinforcement.¹³⁰ Nano-reinforcement from cellulose is more important because it produced nano-composites with economical, light weighted, and better mechanical strength. 

Sustainability of starch nano-crystals

The demand for cutting-edge, sustainable packaging materials with enhanced physical, mechanical, and barrier qualities is rising in the food business. Environmental concerns are brought up by the fact that the materials currently being used are synthetic and not biodegradable. As a result, efforts have been made in recent years to produce sustainable packaging materials consisting of bio-based components. Hence, there is an increasing interest in biobased eco-efficient and high-technology materials from starch.¹³¹ Starch due to its biodegradability, non-toxicity, low cost, abundance in nature, and renewability, is utilized in food packaging, making it the ideal substance for the development of sustainable materials.¹³² Starch nanocrystals (SNC) are crystalline nano-platelets made from the acid hydrolysis of starch which is used as nano-fillers in a polymeric matrix. SNC preparation process is being scale-up due to new applications of starch nanocrystals. But the sustainability of this new bio-based nano-material will depend on its preparation and processing as well as its impacts on the environment.¹¹³ On the other hand, starch films that are filled with starch crystals showed greater UV protection. It is not only biodegradable but also suitable for food packaging. It may also be used to develop edible films as they are obtained from food sources.¹³³ Foam materials produced using cassava starch showed a considerable biodegradation of over 50% after 15 days in the biodegradation test. The results of the study imply that the dual-modified cassava starch-based biodegradable foams have promise for substituting petroleum-based materials in sustainable packaging applications.¹³⁴

Polysaccharides have semi-crystalline structures which offer a great opportunity for the preparation of biobased nanoparticles. Starch is a polysaccharide that is abundantly produced by plant resources. Starch nanocrystals could be prepared by disrupting the starch granules by acid hydrolysis of amorphous parts. Lab-scaled SNCs have been produced with different morphologies with individualized platelets.¹¹³

Safety and regulation of nanomaterials in food packaging

Although the application of nanoparticles in food processing and packaging has advanced significantly, little is known about the toxicity of these materials. Nanoparticles are currently being applied in food products at a rate faster than desired, posing a risk to the environment and human health.¹³⁵ Nanoparticles present in food packaging can enter the respiratory systems of employees and can be exposed to it through the digestive system. Any nanoparticles that enter the respiratory tract are cleared by the mucociliary system before entering the digestive system. Any nanoparticles that penetrate the respiratory tract make their way through the digestive system through mucociliary clearance that will cause serious illness and may sometime be life-threatening.¹³⁶

Hence, it is important to research every aspect of nanoparticle toxicity and environmental behaviour. The effects of food processing and packaging systems based on nanotechnology on human health should be taken into consideration by food regulations. A regulatory framework that can control any risks associated with nanofood and the use of nanotechnologies in the food business is urgently needed. Also, governments must address the broader economic, social, ethical, and civil rights concerns brought on by nanotechnology. Public engagement in decision-making about nanotechnology is essential to ensure the democratic management of these technological advancements in the key domain of agriculture and food.¹³⁷ In 2011, the European Food Safety Authority (EFSA) published a directive titled “on the risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain¹³⁸, outlining the physicochemical information that the manufacturer must submit. Considering the challenges to accurately measure and categorize nanomaterials, EFSA does not explain how these standards might be reached in a consistent and economical way.

Limitations of starch nanocrystals in food packaging

Nanotechnology has been reported to possess great potential for food packaging applications. Nevertheless, a few limitations were noted, including the possibility that products containing nanomaterials may perform novel functions for which it may be challenging to compare them to more traditional functional alternatives, the potential difficulty of developing an inventory due to rapidly evolving production technologies, or the difficulty of assessing the risks associated with nanomaterials due to the dearth of information on their release, exposure, and effects.^135,136

Conclusion

Consumer demand for varieties of food has increased research into the development of more reliable, effective, safe, and eco-friendly food packaging. Nanotechnology as an emerging field has been a source of hope in developing food packaging with improved physical, mechanical, and functional properties. Polysaccharides are major sets of natural biocompatible or biodegradable food packaging materials that could turn around the production of nanocrystals for food packaging applications. Starch which is a most abundant natural biological macromolecule which has great industrial applications, particularly in the packaging sector.  Acid hydrolysis is the most predominant method used for the synthesis of starch nanocrystals. Dilute acids such as sulfuric acid, hydrochloric acid, or oxalic acid were widely used in nanostarch synthesis. The starch nanocrystals synthesized by acid hydrolysis presented an improved mechanical, water barrier, oxygen barrier, and antimicrobial properties of packaging materials and further enhanced the shelf life of the food products. The major limitation of nanotechnology is its complexity in assessing the risks associated with nanomaterials due to the dearth of information on their release, exposure, and effects. The next generation of food packaging will come from biodegradable polymeric materials from nanostarch to give eco-friendly packaging however its toxicological studies should be carried out extensively in the future.

Acknowledgement

The author would like to thank, Department of Food Technology, Hindustan Institute of Technology and Science, (Deemed to be University), Rajiv Gandhi Salai, Padur, Kelambakam, Chennai. Tamil Nadu, India. for their guidance and support to complete this article.

Conflict of Interest

The authors do not have any conflict of interest.

Funding Sources

The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

1. Rahman MS (eds). Handbook of food preservation. 2nd ed. Food science and technology. Boca Raton: CRC Press; 2007.
2. Amit, S. K., Uddin, M., Rahman, R., Islam, S. M., & Khan, M. S. A review on mechanisms and commercial aspects of food preservation and processing. Food Secur. 2017; 6(1):1-22.
3. Vågsholm, I., Arzoomand, N. S., & Boqvist, S. Food security, safety, and sustainability—getting the trade-offs right. Sustain. Food Syst. 2020; 4: 16.
4. Tomaszewska, M., Bilska, B., & Kołożyn-Krajewska, D. The influence of selected food safety practices of consumers on food waste due to its spoilage. International Journal of Environmental Research and Public Health, 2022; 19(13): 8144.
5. Adegoke, G. O., & Olapade, A. A. Preservation of plant and animal foods: An overview. Progress in Food Preservation, First Edition. Edited by Rajeev Bhat, Abd Karim Alias and Gopinadhan Paliyath. John Wiley & Sons, Ltd. 2012.
6. Hammond, S. T., Brown, J. H., Burger, J. R., Flanagan, T. P., Fristoe, T. S., Mercado-Silva, N., … & Okie, J. G. Food spoilage, storage, and transport: Implications for a sustainable future. 2015; 65(8): 758-768.
7. dos Santos Rocha, C., Magnani, M., Ramos, G. L. D. P. A., Bezerril, F. F., de Freitas, M. Q., Cruz, A. G., & Pimentel, T. C. Emerging technologies in food processing: impacts on sensory characteristics and consumer perception. 2022; Current Opinion in Food Science, 100892.
8. Criado, Maria Paula & Fraschini, Carole & Hossain, F. & Lacroix, M. Cellulose Nanocrystals in Food Packaging. 2019.10.1016/B978-0-08-100596-5.22531-6.
9. Pal, M. Nanotechnology: a new approach in food packaging. Food Microbiol. Saf. Hyg. 2019; 2(02): 8-9.
10. Kuswandi, B. “Nanotechnology in food packaging.” Nanoscience in food and agriculture 1. Springer, Cham, 2016; 151-183. DOI: 10.1007/978-3-319-39303-2_6.
11. Agarwal, A., Pathera, A. K., Kaushik, R., Kumar, N., Dhull, S. B., Arora, S., & Chawla, P. Succinylation of milk proteins: Influence on micronutrient binding and functional indices. Trends Food Sci. Technol. 2020; 97: 54–64.
12. Dhull, S. B., Sandhu, K. S., Punia, S., Kaur, M., Chawla, P., Malik, A. Functional, thermal and rheological behavior of fenugreek (Trigonella foenum–graecum L.) gums from different cultivars: A comparative study. J. Biol. Macromol. 2020; 159: 406–414.
13. Reddy, M.M., Vivekanandhan, S., Misra, M., Bhatia, S.K., Mohanty, A.K. Biobased plastics and bionanocomposites: current status and future opportunities. Polym. Sci. 2013; 38: 1653–1689.
14. Adeyeye, S.A.O, Ashaolu, T.J. Applications of nano-materials in food packaging: A review. J Food Process Eng. 2021; 44: e13708.
15. Mazayen, Z. M., Ghoneim, A. M., Elbatanony, R. S., Basalious, E. B., & Bendas, E. R. Pharmaceutical nanotechnology: from the bench to the market. Future Journal of Pharmaceutical Sciences, 2022; 8(1), 12.
16. Guleria, S., Kumar, M., Kumari, S., & Kumar, A. Nano-Starch Films as Effective Antimicrobial Packaging Materials. In Nanotechnological Approaches in Food Microbiology. CRC Press. 2020; pp. 437-453.
17. Martins, P.C., Latorres, J.M., Martins, V.G. Impact of starch nanocrystals on the physicochemical, thermal and structural characteristics of starch-based films. LWT, 2022; 156, p.113041.
18. Fadeyibi A., Osunde Z.D., Agidi G., Evans E.C. Green polymer composites technology: properties and applications. In: S. Inamuddin (Ed.), Mixing index of a starch composite extruder for food packaging application. CRC Press and Taylor & Francis Group, Asia Pacific, 2016; pp 335-346
19. Chinma C.E., Ariahu C.C., Alakali J.S. Effect of temperature and relative humidity on the water vapour permeability and mechanical properties of cassava starch and soy protein concentrate based edible films. Food Sci. Technol. 2015; 52: 2380-6.
20. Lindh, H., Olsson, A., Williams, H. Consumer perceptions of food packaging: contributing to or counteracting environmentally sustainable development?.  Technol. Sci.2016; 29(1), pp.3-23.
21. Marsh, K., & Bugusu, B. Food packaging—roles, materials, and environmental issues. Food Sci. 2007; 72(3): R39-R55.
22. Sarkar, S., & Aparna, K. Food packaging and storage. Research Trends in Home Science and Extension AkiNik Pub, 2020; 3: 27-51.
23. Thomas, K. Effect of food packaging material on the environment. J. Food Sci. 2020; 11(5): 01-02.
24. Bansal, R., & Gupta, G. Plastic in food packaging: Safety concerns for our health and environment. Nutr. Sci. Health Diet. 2020; 1(2): 16-21.
25. United Nations Environment Programme (UNEP) Drowning in Plastics – Marine Litter and Plastic Waste Vital Graphics. 2020.
26. Pongrácz, E. The environmental impacts of packaging. In Book: Environmentally Conscious Materials and Chemicals Processing, 2007; 3: 237-278. DOI: 10.1002/9780470168219.ch9
27. Rochman, C.M., Lewison, R.L., Eriksen, M., Allen, H., Cook, A.M., Teh, S.J. Polybrominated diphenyl ethers (PBDEs) in fish tissue may be an indicator of plastic contamination in marine habitats.  Total Environ.2014; 476, pp.622-633.
28. Lox, F. Packaging and the environment (revised edition). Susan EM Selke of the School of Packaging, Michigan State University, East Lansing, MI, USA. Technomic Publishing Co. Inc. 1994; ISBN 1‐56676‐104‐2, 258 pp.
29. Selke S. Packaging and the environment: alternatives, trends and solutions. CRC Press; 1994 Apr 21.
30. Emamifar, A. Applications of Antimicrobial Polymer Nanocomposites in Food Packaging. In: Hashim, A. editor. Advances in Nanocomposite Technology [Internet]. London: IntechOpen; 2011 DOI: 10.5772/18343.
31. de Moraes, J. O., Müller, C. M. O., & Laurindo, J. B. Influence of the simultaneous addition of bentonite and cellulose fibers on the mechanical and barrier properties of starch composite-films. J. Food Sci. Technol. 2012; 18(1): 35-45.
32. Zhang, J. F., & Sun, X. Mechanical properties of poly (lactic acid)/starch composites compatibilized by maleic anhydride. Biomacromolecules. 2004; 5(4): 1446-1451.
33. Lawal, M. V. Modified starches as direct compression excipients–Effect of physical and chemical modifications on tablet properties: A review. Starch‐Stärke. 2019; 71(1-2): 1800040.
34. Marinopoulou, A., Papastergiadis, E., & Raphaelides, S. N. Inclusion complexes of non‐granular maize starch with fatty acids and ibuprofen. A comparative study of their morphology and structure. Starch‐Stärke, 2019; 71(1-2): 1800100.
35. Aldao, D. C., Šárka, E., Ulbrich, P., & Menšíková, E. Starch nanoparticles–two ways of their preparation. Czech Journal of Food Sciences, 2018; 36(2): 133-138.
36. Lu, H., & Tian, Y. Nanostarch: Preparation, Modification, and Application in Pickering Emulsions. Agric. Food Chem. 2021; 69(25): 6929-6942.
37. Miyazaki, M., Van Hung, P., Maeda, T., & Morita, N. Recent advances in application of modified starches for breadmaking. Trends Food Sci Technol. 2006; 17(11): 591-599.
38. Alwaan,M., Kamel,A.H. Preparation and Properties of Starch Nanocrystals (SNC) using Sulfuric Acid as Acid Hydrolysis of Corn Starch, J. Adv. Sci. Eng. Technol. 2018; 6: 75-77.
39. Yazid, N.S.M., Abdullah, N., Muhammad, N., Matias-Peralta, H.M. Application of starch and starch-based products in food industry.  Sci.Technol. 2018; 10(2).
40. Santana, Á. L., Meireles, M. A. A. New starches are the trend for industry applications: a review. Food Public Health. 2014;  4(5): 229-241.
41. Yazid, N. S. M., Abdullah, N., Muhammad, N., & Matias-Peralta, H. M. Application of starch and starch-based products in food industry. Sci. Technol. 2018; 10(2).
42. Sozer, N., Kokini, J. L. Nanotechnology and its applications in the food sector. Trends Biotechnol. 2009; 27(2): 82-89.
43. Punia, S., Sandhu, K. S., Dhull, S. B., and Kaur, M. Dynamic, shear and pasting behaviour of native and octenyl succinic anhydride (OSA) modified wheat starch and their utilization in preparation of edible films. J. Biol. Macromol. 2019; 133: 110–116.
44. Le Corre, D., & Angellier-Coussy, H. Preparation and application of starch nanoparticles for nanocomposites: A review. React Funct Polym. 2014; 85: 97-120.
45. González, K., Retegi, A., González, A., Eceiza, A., & Gabilondo, N. Starch and cellulose nanocrystals together into thermoplastic starch bionanocomposites. Polym. 2015; 117: 83-90.
46. Chen, Y., Y. Hao, K. Ting, Q. Li Q. Gao. “Preparation and emulsification properties of dialdehyde starch nanoparticles.” Food Chem. 2019; 286: 467-474.
47. Li, C., Sun, P., & Yang, C. Emulsion stabilized by starch nanocrystals. Starch‐Stärke, 2012; 64(6): 497-502.
48. Haaj, S. B., Thielemans, W., Magnin, A., & Boufi, S. Starch nanocrystal stabilized Pickering emulsion polymerization for nanocomposites with improved performance. ACS Appl. Mater. Interfaces. 2014; 6(11): 8263-8273.
49. Gardouh, A., Srag El-Din, A. S., Moustafa, Y., Gad, S. Formulation factors of starch-based nanosystems preparation and their pharmaceutical application. Records Pharm. Biomed. Sci. 2021; 5: 28-39.
50. Nieto-Suaza, L., Acevedo-Guevara, L., Sánchez, L. T., Pinzón, M. I., & Villa, C. C. Characterization of Aloe vera-banana starch composite films reinforced with curcumin-loaded starch nanoparticles. Food Struct. 2019; 22: 100131.
51. Shi AM, Li D, Wang LJ, et al. Preparation of starch-based nanoparticles through highpressure homogenization and miniemulsion cross-linking: Influence of various process parameters on particle size and stability. Polym. 2011; 83:1604-1610.
52. LeCorre, D., Vahanian, E., Dufresne, A., Bras, J. Enzymatic pretreatment for preparing starch nanocrystals. Biomacromolecules. 2012; 13(1): 132-137.
53. Shabana, S., Prasansha, R., Kalinina, I., Potoroko, I., Bagale, U., Shirish, S. H. Ultrasound assisted acid hydrolyzed structure modification and loading of antioxidants on potato starch nanoparticles. Sonochem. 2019; 51: 444-450.
54. Hedayati, S., Niakousari, M., Mohsenpour, Z. Production of tapioca starch nanoparticles by nanoprecipitation-sonication treatment. J. Biol. Macromol. 2020; 143: 136-142.
55. Acevedo-Guevara, L., Nieto-Suaza, L., Sanchez, L. T., Pinzon, M. I., & Villa, C. C. Development of native and modified banana starch nanoparticles as vehicles for curcumin. J. Biol. Macromol. 2018; 111: 498-504.
56. Minakawa, A. F. K., P. C. S. Faria-Tischer and S. Mali. Simple ultrasound method to obtain starch micro- and nanoparticles from cassava, corn and yam starches. Food Chem. 2019; 283: 11-18.
57. Momenpoor, B., Danafar, F., Bakhtiari, F. Size Controlled Preparation of Starch Nanoparticles from Wheat Through Precipitation at Low Temperature. Nano Res. 2019; 56: 131-141.
58. Ahmad, M., Gani, A., Hassan, I., Huang, Q., Shabbir, H. Production and characterization of starch nanoparticles by mild alkali hydrolysis and ultra-sonication process. Rep. 2020; 10(1): 1-11.
59. Guo, Z., Zhao, B., Chen, L., Zheng, B. Physicochemical Properties and Digestion of Lotus Seed Starch under High-Pressure Homogenization. Nutrients. 2019; 11(2): 371.
60. Nascimento, T. A., Calado, V., Carvalho, C. W. P. Development and characterization of flexible film based on starch and passion fruit mesocarp flour with nanoparticles. Food Res. J. 2012; 49(1): 588-595.
61. Martins, P. C., Latorres, J. M., Martins, V. G. Impact of starch nanocrystals on the physicochemical, thermal and structural characteristics of starch-based films. LWT, 2022; 113041.
62. Dukare, A. S., Arputharaj, A., Bharimalla, A. K., Saxena, S., Vigneshwaran, N. Nanostarch production by enzymatic hydrolysis of cereal and tuber starches. Polym. 2021; 2: 100121.
63. Hakke, V. S., Bagale, U. D., Boufi, S., Babu, G. U. B., Sonawane, S. H. Ultrasound assisted synthesis of starch nanocrystals and it’s applications with polyurethane for packaging film. J Renew Mater. 2020, 8(3), 239.
64. Lin, N., Huang, J., Chang, P. R., Anderson, D. P., Yu, J. Preparation, modification, and application of starch nanocrystals in nanomaterials: a review. Nanomater. 2011; 2011.
65. Velásquez-Castillo, L. E., Leite, M. A., Ditchfield, C., do Amaral Sobral, P. J., & Moraes, I. C. F. Quinoa starch nanocrystals production by acid hydrolysis: kinetics and properties. J. Biol. Macromol. 2020; 143: 93-101.
66. Babu, A. S., Parimalavalli, R., Jagannadham, K., Rao, J. S. Chemical and structural properties of sweet potato starch treated with organic and inorganic acid. Food Sci. Technol. 2015; 52(9): 5745-5753.
67. Kim, H. Y., Park, S. S., Lim, S. T. Preparation, characterization and utilization of starch nanoparticles. Colloids Surfac. B: Biointerfaces. 2015; 126: 607-620.
68. Le Corre, D., Bras, J., Dufresne, A. Starch nanoparticles: a review. Biomacromolecules, 2010; 11(5): 1139-1153.
69. Angellier, H., Choisnard, L., Molina-Boisseau, S., Ozil, P., Dufresne, A. Optimization of the preparation of aqueous suspensions of waxy maize starch nanocrystals using a response surface methodology. Biomacromolecules, 2004; 5(4): 1545-1551.
70. Da Silva, N. M. C., de Lima, F. F., Fialho, R. L. L., Albuquerque, E. C. D. M. C., Velasco, J. I., Fakhouri, F. M. Production and characterization of starch nanoparticles. In Applications of Modified Starches, 2018; 41-48, United Kingdom: IntechOpen.
71. Singh, T., Shukla, S., Kumar, P., Wahla, V., Bajpai, V. K., Rather, I. A. Application of nanotechnology in food science: perception and overview. Microbiol. 2017; 8: 1501.
72. Zhou, L., Fang, D., Wang, M., Li, M., Li, Y., Ji, N., … Sun, Q. Preparation and characterization of waxy maize starch nanocrystals with a high yield via dry-heated oxalic acid hydrolysis. Food Chem. 2020; 318: 126479.
73. Aldao, D.C., Šárka, E., Ulbrich, P., Menšíková, E. Starch nanoparticles–two ways of their preparation. Czech J. Food Sci.2018; 36(2), pp.133-138.
74. Kim, J. Y., & Lim, S. T. Preparation of nano-sized starch particles by complex formation with n-butanol. Polym. 2009; 76(1): 110-116.
75. Sun, Q., Li, G., Dai, L., Ji, N., Xiong, L. Green preparation and characterisation of waxy maize starch nanoparticles through enzymolysis and recrystallisation. Food Chem. 2014; 162: 223-228.
76. Hao, Y., Chen, Y., Li, Q., & Gao, Q. Preparation of starch nanocrystals through enzymatic pretreatment from waxy potato starch. Polym. 2018; 184: 171-177.
77. Babu, A. S., Mohan, R. J., Parimalavalli, R. Effect of single and dual-modifications on stability and structural characteristics of foxtail millet starch. Food Chemistry, 2019a; 271: 457-465.
78. Babu, A. S., Mohan, R. J. Influence of prior pre-treatments on molecular structure and digestibility of succinylated foxtail millet starch. Food Chem. 2019b; 295: 147-155.
79. Amini, A. M., Razavi, S. M. A. A fast and efficient approach to prepare starch nanocrystals from normal corn starch. Food Hydrocoll. 2016; 57: 132-138.
80. Frone, A. N., Panaitescu, D. M., Donescu, D., Spataru, C. I., Radovici, C., Trusca, R., Somoghi, R. Preparation and characterization of PVA composites with cellulose nanofibers obtained by ultrasonication. 2011; 6(1): 487-512.
81. Wang, H., Li, D., Zhang, R. Preparation of ultralong cellulose nanofibers and optically transparent nanopapers derived from waste corrugated paper pulp. 2013; 8(1): 1374–1384.
82. Tang, Y., Yang, S., Zhang, N., Zhang, J. Preparation and characterization of nanocrystalline cellulose via low-intensity ultrasonic-assisted sulfuric acid hydrolysis. Cellulose. 2014; 21(1): 335–346. DOI 10.1007/s10570-013-0158-2.
83. Liu, C., Li, M., Ji, N., Liu, J., Xiong, L., Sun, Q. Morphology and characteristics of starch nanoparticles self-assembled via a rapid ultrasonication method for peppermint oil encapsulation. Agric. Food Chem. 2017; 65(38): 8363-8373.
84. Al-Aseebee, M. D. F., Rashid, A. H., Naje, A. S., Jayara, J. J., Maridurai, T. Influence of rice starch nanocrystals on the film properties of the bionanocomposite edible films produced from native rice starch. J. Nanomater. Biostructures. 2021; 16(2): 697-704.
85. Li, X., Qin, Y., Liu, C., Jiang, S., Xiong, L., Sun, Q. Size-controlled starch nanoparticles prepared by self-assembly with different green surfactant: the effect of electrostatic repulsion or steric hindrance. Food Chem. 2016; 199: 356-363.
86. Li, P., He, X., Dhital, S., Zhang, B., Huang, Q. Structural and physicochemical properties of granular starches after treatment with debranching enzyme. Polym. 2017; 169, 351-356.
87. Dai, L., Li, C., Zhang, J., Cheng, F. Preparation and characterization of starch nanocrystals combining ball milling with acid hydrolysis. Polym. 2018; 180: 122-127.
88. Wang, H., Liu, C., Shen, R., Gao, J., Li, J. An efficient approach to prepare water-redispersible starch nanocrystals from waxy potato starch. Polymers, 2021; 13(3): 431.
89. Winarti, C., Surono, I. S., & Uswah, M. Effect of acid and hydrolysis duration on the characteristics of arrowroot and taro starch nanoparticles. In IOP Conference Series: Earth and Environmental Science. 2019; 309(1): 012039. IOP Publishing.
90. Chang Y, Yan X, Wang Q, Ren, L., Tong, J., Zhou, J. High efficiency and low cost preparation of size controlled starch nanoparticles through ultrasonic treatment and precipitation. Food Chem. 2017;227:369-375.
91. Gutiérrez, G., Morán, D., Marefati, A., Purhagen, J., Rayner, M., Matos, M. Synthesis of controlled size starch nanoparticles (SNPs). Polym. 2020, 250, 116938.
92. Nlandu, H., Chorfa, N., Belkacemi, K., & Hamoudi, S. Potato Starch Nanocrystal Preparation via Supercritical Carbon Dioxide Pretreatment Combined with Enzymatic Hydrolysis. BioResources. 2021; 16(4): 7671-7683.
93. Dai, L., Zhang, J., Cheng, F. Succeeded starch nanocrystals preparation combining heat-moisture treatment with acid hydrolysis. Food chem. 2019, 278, 350-356.
94. Juna, S., Hayden, S., Damm, M., Kappe, C. O., Huber, A. Microwave mediated preparation of nanoparticles from wx corn starch employing nanoprecipitation. Starch‐Stärke, 2014; 66(3-4): 316-325.
95. Gonçalves, P.M., Noreña, C.P.Z., da Silveira, N.P., et al. Characterization of starch nanoparticles obtained from Araucaria angustifolia seeds by acid hydrolysis and ultrasound. LWT—Food Sci. Technol. 2014; 58:21-27.
96. Fu, Z.Q., Wang, L.J., Li, D., et al. Effects of high-pressure homogenization on the properties of starch-plasticizer dispersions and their films. Polym. 2011;86:202-207.
97. Haaj, S.B., Magnin, A., Pétrier, C., et al. Starch nanoparticles formation via high power ultrasonication. Polym. 2013;92:1625-1632.
98. Li, X., Qiu, C., Ji, N., et al. Mechanical, barrier and morphological properties of starch nanocrystals-reinforced pea starch films. Polym. 2015;121:155-162.
99. Jiang, S., Liu, C., Wang, X., et al. Physicochemical properties of starch nanocomposite films enhanced by self-assembled potato starch nanoparticles. LWT—Food Sci. Technol. 2016;69:251-257.
100. Pagno, C.H., Costa, T.M.H., De Menezes, E.W., et al. Development of active biofilms of quinoa (Chenopodium quinoa W.) starch containing gold nanoparticles and evaluation of antimicrobial activity. Food Chem. 2015;173:755-762.
101. González Seligra, P., Eloy Moura, L., Famá, L., et al. Influence of incorporation of starch nanoparticles in PBAT/TPS composite films. Int. 2016;65:938-945.
102. Costa, É.K. de C., de Souza, C.O., da Silva, J.B.A., et al. Hydrolysis of part of cassava starch into nanocrystals leads to increased reinforcement of nanocomposite films. Appl. Polym. Sci. 2017; 134: 45311.
103. Flores, S.  Famá, L.  Rojas, A.M. Goyanes, S.& Gerschenson L. Physical properties of tapioca-starch edible films: influence of filmmaking and potassium sorbate. Food Res. Int. 2007; 40: 257-265.
104. Goudarzi, V.  Shahabi-Ghahfarrokhi, I. Babaei-Ghazvini A. Preparation of ecofriendly UV-protective food packaging material by starch/TiO2 bio-nanocomposite: Characterization. Int. Biol. Macromol. 2017; 95: 306-313.
105. Jayakumar, A.  Heera,  K.V.  Sumi, T.S.  Joseph, M.  Mathew, S.  Praveen, G.  Indu, C. Radhakrishnan, E.K.  Starch-PVA composite films with zinc-oxide nanoparticles and phytochemicals as intelligent PH sensing wraps for food packaging application. J. Biol. Macromol. 2019; 136: 395-403.Xie, F.,  Pollet, E., Halley, P.J., Avérous, L. Starch-based nano-biocomposites. Prog. Polym. Sci., 2013; 38: 1590-1628
106. Wang, X.L., Yang, K.K., Wang, Y.Z. Properties of starch blends with biodegradable polymers. Macromol. Sci. Polym. Rev. 2003; 43: 385-409.
107. Chaudhary, A.L.,  Miler, M.,  Torley, P.J.,  Sopade, P.A., Halley P.J., Amylose content and chemical modification effects on the extrusion of thermoplastic starch from maize. Polym. 2008, 74: 907-913.
108. Volkert, B.,  Lehmann, A.,  Greco, T., Nejad, M.H. A comparison of different synthesis routes for starch acetates and the resulting mechanical properties. Polym. 2010; 79: 571-577.
109. Le Corre, D., Bras, J., Dufresne A. Starch nanoparticles: a review Biomacromolecules, 2010; 11: 1139-1153.
110. Chausali, N., Saxena, J., Prasad, R. Recent trends in nanotechnology applications of bio-based packaging. Journal of Agriculture and Food Research, 2022; 7: 100257.
111. Li, X., Qiu, C., Ji, N., Sun, C., Xiong, L., Sun, Q. Mechanical, barrier and morphological properties of starch nanocrystals-reinforced pea starch films.  Polym. 2015; 121, pp.155-162.
112. Wang, H., Qian, J., Ding F., Emerging chitosan-based films for food packaging applications. Agric. Food Chem.2018; 66 (2): 395-413.
113. Sriupayo, J., Supaphol, P., Blackwell, J., Rujiravanit R. Preparation and characterization of α-chitin whisker-reinforced chitosan nanocomposite films with or without heat treatment. Polym.2005; 62: 130-136.
114. Roy, K., Thory, R., Sinhmar, A., Pathera, A.K., Nain, V. Development and characterization of nano starch-based composite films from mung bean (Vigna radiata).  J. Biol. Macromol.2020; 144, pp.242-251.
115. Mukurumbira, A.R., Mellem, J.J., Amonsou, E.O. Effects of amadumbe starch nanocrystals on the physicochemical properties of starch biocomposite films.  Polym.2017; 165, 142-148.
116. Piyada, K., Waranyou, S., Thawien, W. Mechanical, thermal and structural properties of rice starch films reinforced with rice starch nanocrystals. Food Res. J.2013; 20(1), 439.
117. Chang, P.R.,  Jian, R., Yu, J., Ma X. Starch-based composites reinforced with novel chitin nanoparticles. Polym., 2010a; 80: 420-425.
118. Chang, R., Jian, R., Yu, J., Ma X., Fabrication and characterisation of chitosan nanoparticles/plasticisedstarch composites. Food Chem.2010b; 120: 736-740.
119. Casariego, A., Souza, B.W.S.,  Cerqueira, M.A., Teixeira, J.A., Cruz, L., Díaz, R., Vicente, A.A. Chitosan/clay films’ properties as affected by biopolymer and clay micro/nanoparticles’ concentrations. Food Hydrocolloids, 2009; 23: 1895-1902.
120. Lavorgna, M.,  Piscitelli, F., Mangiacapra, P., Buonocore, G.G.,  Study of the combined effect of both clay and glycerol plasticizer on the properties of chitosan films. Polym. 2010; 82: 291-298.
121. Abdollahi, M.,  Rezaei, M.,  Farzi G. A novel active bionanocomposite film incorporating rosemary essential oil and nanoclay into chitosan. Food Eng.2012; 111: 343-350.
122. Hsu, S.H.,  Wang, M.C., Lin, J.J. Biocompatibility and antimicrobial evaluation of montmorillonite/chitosan nanocomposites. Clay Sci.2012; 56: 53-62.
123. Brinchi, L., Cotana, F., Fortunati, E., Kenny J.M., Production of nanocrystalline cellulose from lignocellulosic biomass: technology and applications. Polym.  2013; 94: 154-169.
124. Dufresne, A. Processing of polymer nanocomposites reinforced with polysaccharide nanocrystals. Molecules, 2010; 15(6): 4111-4128.
125. Duran, N.,  Lemes, A.P., Duran, M.,  Freer, J.,  Baeza J., A minireview of cellulose nanocrystals and its potential integration as co-product in bioethanol production. Chil. Chem. Soc., 2011; 56: 672-677.
126. Eichhorn, S. J., Dufresne, A., Aranguren, M., Marcovich, N. E., Capadona, J. R., Rowan, S. J., … & Peijs, T. Current international research into cellulose nanofibres and nanocomposites. Mater. Sci. 2010; 45: 1-33.
127. Velásquez-Cock, J., Ramírez, E., Betancourt, S., Putaux, J. L., Osorio, M., Castro, C., … & Zuluaga, R. Influence of the acid type in the production of chitosan films reinforced with bacterial nanocellulose.  J. Biol. Macromol.2014; 69: 208-213.
128. Azizi Samir, M.A.S.,  Alloin, F., Dufresne A., Review of recent research into cellulosic whiskers, their properties and their application in nanocomposite field. 2005; 6: 612-626.
129. Wan, Y.Z.,  Luo, H.,  He, F. , Liang, H., Huang, Y.,  Li X.L. Mechanical, moisture absorption, and biodegradation behaviours of bacterial cellulose fibre-reinforced starch biocomposites. Sci. Technol.2009; 69: 1212-1217.
130. Zhong, C. Industrial-scale production and applications of bacterial cellulose. Bioeng. Biotechnol. 2020; 8: 605374.
131. Silva, F.A., Dourado, F., Gama, M., Poças, F. Nanocellulose bio-based composites for food packaging. 2020; 10(10), p.2041.
132. Chen, Q., Shi, Y., Chen, G. and Cai, M. Enhanced mechanical and hydrophobic properties of composite cassava starch films with stearic acid modified MCC (microcrystalline cellulose)/NCC (nanocellulose) as strength agent. Int. J. Biol. Macromol. 2020; 142, 846-854.
133. Amjad, A., Anjang Ab Rahman, A., Awais, H., Zainol Abidin, M.S., Khan, J. A review investigating the influence of nanofiller addition on the mechanical, thermal and water absorption properties of cellulosic fibre reinforced polymer composite.  Ind. Text.2022; 51, 65S-100S.
134. Amaraweera, S.M., Gunathilake, C., Gunawardene, O.H., Dassanayake, R.S., Fernando, N.M., Wanninayaka, D.B., Rajapaksha, S.M., Manamperi, A., Gangoda, M., Manchanda, A., Fernando, C.A. Preparation and characterization of dual-modified cassava starch-based biodegradable foams for sustainable packaging applications. ACS omega, 2022; 7(23), 19579-19590.
135. Ranjan, S., Dasgupta, N., Chakraborty, A.R., Melvin Samuel, S., Ramalingam, C., Shanker, R., Kumar, A. Nanoscience and nanotechnologies in food industries: opportunities and research trends.  Nanopart Res.2014; 16, pp.1-23.
136. Ameta, S.K., Rai, A.K., Hiran, D., Ameta, R., Ameta, S.C. Use of nanomaterials in food science. Biogenic nano-particles and their use in agro-ecosystems, 2020; 457-488.
137. Sodano, V., Gorgitano, M.T., Verneau, F., Vitale, C.D. Consumer acceptance of food nanotechnology in Italy.  Food J. 2016; 118 (30), 714-733.
138. EFSA Scientific Committee. Guidance on the risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain. EFSA Journal, 2011; 9(5), 2140.