Food nanotechnology – an overview

Abstract

Food nanotechnology is an area of emerging interest and opens up a whole universe of new possibilities for the food industry. The basic categories of nanotechnology applications and functionalities currently in the development of food packaging include: the improvement of plastic materials barriers, the incorporation of active components that can deliver functional attributes beyond those of conventional active packaging, and the sensing and signaling of relevant information. Nano food packaging materials may extend food life, improve food safety, alert consumers that food is contaminated or spoiled, repair tears in packaging, and even release preservatives to extend the life of the food in the package. Nanotechnology applications in the food industry can be utilized to detect bacteria in packaging, or produce stronger flavors and color quality, and safety by increasing the barrier properties. Nanotechnology holds great promise to provide benefits not just within food products but also around food products. In fact, nanotechnology introduces new chances for innovation in the food industry at immense speed, but uncertainty and health concerns are also emerging. EU/WE/global legislation for the regulation of nanotechnology in food are meager. Moreover, current legislation appears unsuitable to nanotechnology specificity.

Introduction

The word “nano” comes from the Greek for “dwarf”. A nanometer is a thousandth of a thousandth of a thousandth of a meter (10⁻⁹ m). One nanometer is about 60,000 times smaller than a human hair in diameter or the size of a virus, a typical sheet of paper is about 100,000 nm thick, a red blood cell is about 2,000 to 5,000 nm in size, and the diameter of DNA is in the range of 2.5 nm. Therefore, nanotechnology deals with matter that ranges from one-half the diameter of DNA up to 1/20 the size of a red blood cell.¹ Further, it is interesting to note that nanomaterials are so small, even bacteria would need a microscope to see them.² Nanoparticles are generally accepted as those with a particle size below 100 nanometers where unique phenomena enable novel applications and benefits. Nanomaterials on which most of the research has been carried out are normally powders composed of nanoparticles which exhibit properties that are different from powders of the same chemical composition, but with much larger particles. Research is in progress into their potential in food nanotechnology sector including food packaging, foods and supplements due to their unique functions and applications of nanomaterials.³ Tens of millions of dollars are being spent in a global race to apply nanotechnologies in food production, processing and packaging.

Natural self-assembled nanostructures

Many natural foods contain nanoscale components and their properties are determined by their structure. These have been eaten safely for generations. In fact, some of food’s most important raw materials [proteins, starches, and fats] undergo structural changes at the nanometer and micrometer scales during normal food processing.⁴ Food proteins (for example, native beta-lactoglobulin, which is about 3.6 nm in length) can undergo denaturation (via pressure, heat, pH, etc.) and the denatured components reassemble to form larger structures, like fibrils or aggregates, which in turn can be assembled to form even larger gel networks (eg, yogurt). Self-assembled nanotubes from hydrolyzed milk protein α-lactalbumin, a potential new carrier for nanoencapsulation of nutrients, supplements, and pharmaceuticals, have been reported.⁵ Casein micelles may be useful as nanovehicles for entrapment, protection and delivery of sensitive hydrophobic nutraceuticals within other food products.⁶ Protein-polysaccharide mixed solutions can spontaneously separate into a phase with nano- or microsized droplets dispersed in a continuous phase. Starch granules expand when heated and hydrated releasing biopolymers that can be recrystallized into nanosized structures (eg, recrystallized amylose regions may be about 10–20 nm); dextrins and other degradation products of extrusion can be used to encapsulate bioactive substances in microregions, etc. In the case of fats, monoglycerides, for example, can selfassemble into many morphologies at the nanoscale level, and hierarchically structured into tryglicerides can be crystallites (10–100 nm), followed by arrangement into large clusters, then flocs, and finally, fat crystal networks.²

Screening of pea varieties using microscopic methods has identified commercial varieties, such as Greenshaft, that contain blends of normal starches and these ‘naturally resistant’ novel starches. The nanostructured food ingredients are being developed with the claims that they offer improved taste, texture and consistency⁷ For example, low-fat nanostructured mayonnaise spreads and ice creams claim to be as “creamy” as their full fat alternatives and hence, offer a healthier option to the consumer.⁷ Natural nanostructures found in foods are produced by some proteins and carbohydrates. Examples include digestion of food and food structure building processes, such as the arrangement of amylose and amylopectin in a starch granule. A cow’s udder was given as an example of a nano device synthesizing, assembling, and dispensing proteins and fat into an aqueous phase, where they later become building blocks for a myriad of protein structures. Such processes cause microstructural changes in food, such as homogenization and fine milling. Homogenized milk has a nanostructure of 100 nm sized droplets in it.⁸ The dairy industry utilizes three basic microsized and nanosized structures (casein micelles, fat globules, whey proteins) to build all sorts of emulsions (butter), foams (ice cream and whipped cream), complex liquids (milk), plastic solids (cheese), and gel networks (yogurt).⁹ In fact, dairy technology is not just a microtechnology but also a nanotechnology, and it has existed for a long time.

Research into naturally occurring nanostructures in foods is mainly designed to improve the functional behavior of the food. The present research has been focused on modifying food substances to produce nanoparticles that have a different function from the original substance. Early examples from the patent literature and marketing brochures are a number of oxides, such as titanium dioxide and silicon dioxide. The former has conventionally been used as a color and the latter as a flow agent in foods.¹⁰ Nanotechnology can be applied in all phases of the food cycle – from farm to fork.¹¹ Food packaging is the one sector of the industry where nanotechnology applications are beginning to live up to their promise and nanocomposites is the rapidly growing field.¹² Most food packaging applications developed to date have incorporated metal or oxide particles, or more commonly nanoclays.

The understanding of food materials and food processing at the nanoscale is important to create new and improved food products. Moreover, the potential for nanotech food seems unlimited. In the food industry, nanotechnology has thrilled manufacturers as its potential uses are explored, including detecting bacteria in packaging, or producing stronger flavors and colorings. Currently, the number of food products using nanotechnology of any kind is relatively small. Most of the nanotechnology is still only a promise for enabling new food products: some or many years in the future. Nanotechnology may revolutionize the food system and has the potential to influence the science of food in a positive way, as it could generate innovation in food texture, taste, processability, and stability during shelf life.¹³ The design and application of nanoderived assemblies as tools for improved delivery and bioavailability of bioactive nutrients were reported.^14,15 Nanotechnology is quickly moving from the laboratory onto supermarket shelves and our kitchen tables and has the potential to revolutionize food systems.¹⁶ Further, worldwide commercial foods and food supplements containing added nanoparticles are becoming available. Nanotechnology promises big benefits for food safety, quality, and shelf life, provided the challenges it brings can be overcome.¹⁷ Scientists are of the opinion that nanomaterials are fundamentally different substances that create new and unique risks to human health and the environment and require new forms of safety monitoring.

Types of nanomaterials and nanostructures

The novel properties of nanomaterials offer many new opportunities for the food industry¹⁸ Different types of functional nanostructures can be used as building blocks to create novel structures and introduce new functionalities into foods. These include: nanoliposomes, nanoemulsions, nanoparticles and nanofibers. Weiss has described several of these structures, their actual and potential uses in the food industry^19,20 According to the currently available information, nanomaterials used in food applications include both inorganic and organic substances. Engineered nanomaterials (ENMs) which are likely to be found in nanofood products fall into three main categories: inorganic, surface functionalized materials, and organic engineered nanomaterials.³

Inorganic nanomaterials for application in food food additives, food packaging or storage include ENMs of transition metals, such as silver and iron; alkaline earth metals, such as calcium and magnesium; and non-metals, such as selenium and silicates. Other ENMs that can potentially be used in food applications include titanium dioxide. Food packaging is the major area of application of metal (oxide) ENMs. Nanosilver is finding a growing use in a number of consumer products, including food and health food water, and food contact surfaces and packaging materials. Indeed the use of nanosilver as an antimicrobial, antiodorant, and a (proclaimed) health supplement has already surpassed all other ENMs currently in use in different sectors.²¹ Amorphous nanosilica is known to be used in food contact surfaces and food packaging applications. Nanoselenium is being marketed as an additive to a green tea product, with a number of (proclaimed) health benefits resulting from enhanced uptake of selenium. Nanocalcium salts are the subject of patent applications²² for intended use in chewing gums. Nanocalcium and nanomagnesium salts are also available as health supplements. Nano-iron is available as a health supplement and is used in the treatment of contaminated water, where it is claimed to decontaminate water by breaking down organic pollutants and killing microbial pathogens. A soluble nanomaterial under development is nanosalt, which will enable consumers to cut down their salt intake, since a small amount will cover a larger area of the food surface.²³ Cola-tasting nanomilk and fat-reduced nanomayonnaise are just two of the nanotechnology-based food products in the pipeline from Wageningen University in Holland. Nanotechnology would even be used to manufacture ‘smart’ packaging to dramatically extend the shelf life of food and enable it to be transported even further.²⁴ Smart’ packaging (containing nanosensors and antimicrobial activators) is being developed that will be capable of detecting food spoilage and releasing nanoantimicrobes to extend food shelf life, enabling supermarkets to keep food for even greater periods before its sale. Nanosensors, embedded into food products as tiny chips invisible to the human eye, would also act as electronic barcodes.²⁵

Surface functionalized nanomaterials add certain types of functionality to the matrix, such as antimicrobial activity or a preservative action through absorption of oxygen. For food packaging materials, functionalized ENMs are used to bind with the polymer matrix to offer mechanical strength or a barrier against movement of gases, volatile components (such as flavors) or moisture. Compared to inert nanomaterials, they are more likely to react with different food components, or become bound to food matrices, and hence may not be available for migration from packaging materials, or translocation to other organs outside the GI tract. The nanoclay mineral is mainly montmorillonite (also termed as bentonite), which is natural clay obtained from volcanic ash/rocks. Nanoclay has a natural nanoscaled layer structure and is organically modified to bind to polymer matrices. The use of functionalized nanoclays in food packaging can help to develop materials with enhanced gas-barrier properties.

Organic nanomaterials (many of them naturally-occurring substances) are used (or have been developed for use) in food/feed products for their increased uptake and absorption, and improved bioavailability of vitamins, antioxidants in the body, compared to conventional bulk equivalents. A wide range of materials are available in this category, for example food additives (eg, benzoic acid, citric acid, ascorbic acid) and supplements (eg, vitamins A and E, isoflavones, beta-carotene, lutein, omega-3 fatty acids, and coenzyme-Q₁₀). An example of an organic nanomaterial is the tomato carotenoid lycopene. A synthetic nanosized form of lycopene has been produced and found as equivalent sources of lycopene compared to natural lycopene.²⁶ Proteins, fat and sugar molecules, as well as neutraceuticals consisting of food additives derived from plants, are examples of organic nanomaterials.

Nanotechnology analysts estimated that between 150–600 nanofoods and 400–500 nano food packaging applications are already on the market.^27,28 Nanotechnology has also opened the way for the introduction of other functionalities, such as antimicrobial activity in biodegradable materials. For instance, the preservative benzoic acid has been bonded to a magnesium–aluminium hydrotalcite and the complex has been blended with polycaprolactone to slow down the release of the antimicrobial molecule.²⁹ Other developments include the use of certain enzymes with antimicrobial activity that could be covalently immobilized on to amino- or carboxyl-plasma-activated bio-oriented polypropylene films via suitable coupling agents.³⁰

Potential food applications

A number of recent reports and reviews have identified the current and short-term projected applications of nanotechnologies for the food sector.^31–36 The main areas of application include food packaging and food products that contain nanosized or nanoencapsulated ingredients and additives. The potential for food nanotechnology applications seems unlimited. All facets of the food industry from ingredients to packaging to food analysis methods are already looking into nanotech applications. These are resulting in numerous promising applications for improved food production, processing, packaging, and storage.^37–42 Bacteria identification and food quality monitoring using biosensors; intelligent, active, and smart food packaging systems; nanoencapsulation of bioactive food compounds are a few examples of emerging applications of nanotechnology for the food industry⁴³ Carbon nanotubes can be used in food packaging to improve its mechanical properties. It has been recently discovered that carbon nanotubes exhibited powerful antimicrobial effects and Escherichia coli bacteria died on immediate direct contact with aggregates of carbon nanotubes.⁴⁴ In fact, the long, thin nanotubes puncture E. coli cells, causing cellular damage.⁴⁵ Applications of nanotechnology in organic food production require precaution, as little is known about their impact on environment and human health.⁴⁶ Some recent food applications of nanotechnology, safety and risk problems of nanomaterials, routes for nanoparticles entering the body, existing regulations of nanotechnology in several countries, and a certification system of nanoproducts were reported.^47,48 Increasing uses of tools and techniques developed by nanotechnology to detect carcinogenic pathogens and biosensors for improved and contamination free food have been reported.⁴⁹

Functionalized nanostructured materials are finding applications in many sectors of the food industry, including novel nanosensors, new packaging materials with improved mechanical and barrier properties, and efficient and targeted nutrient delivery systems.⁵⁰ Scientists have provided insights into the potential benefits of nanotechnology in food safety⁵¹ The main achievements, such as harnessing the casein micelle, a natural nanovehicle of nutrients, for delivering hydrophobic bioactives; discovering unique nanotubes based on enzymatic hydrolysis of a-lactalbumin; introduction of novel encapsulation techniques based on cold-set gelation for delivering heat-sensitive bioactives including probiotics; developments and use of Maillard reaction based conjugates of milk proteins and polysaccharides for encapsulating bioactives; introduction of β-lactoglobulin-pectin nanocomplexes for delivery of hydrophobic nutraceuticals in clear acid beverages; development of core-shell nanoparticles made of heat-aggregated β-lactoglobulin, nanocoated by beet-pectin, for bioactive delivery; synergizing the surface properties of whey proteins with stabilization properties of polysaccharides in advanced W/O/W and O/W/O double emulsions; application of milk proteins for drug targeting, including lactoferrin or bovine serum albumin conjugated nanoparticles for effective in vivo drug delivery across the blood-brain barrier; beta casein nanoparticles for targeting gastric cancer; fatty acid-coated bovine serum albumin nanoparticles for intestinal delivery, and Maillard conjugates of casein and resistant starch for colon targeting were reported.⁵² DNA microarrays, microelectromechanical systems and microfluidics technologies will enable the realization of the potential of nanotechnology for food applications. Nanocharcoal® adsorbent finds applications such as decoloration of food products.⁵³

Analytical food nanotechnology

Detection and characterization of nano delivery systems is an essential part of understanding the benefits, as well as the potential toxicity of these systems in food. A detailed description of food nano delivery systems based on lipids, proteins, and/or polysaccharides, and the current analytical techniques used for the identification and characterization of these delivery systems in food products has been reported.⁵⁴

The analytical approaches have been subdivided into three groups; separation techniques, imaging techniques, and characterization techniques. The recent progress made in analytical nanotechnology, as applied to the food industry and to food analysis; with particular emphasis on nanosensing have been reported.⁵⁵ The electronic nose is a device that uses an array of chemical sensors tied to a data-processing system that mimics the way a nose works. A new strategy for feature selection has been introduced to MS-based electronic nose applications. Its fine performance has been demonstrated using two MS e-nose databases.⁵⁶ Detection of fruit odors using an electronic nose has been reported.⁵⁷ Methods have been reported to estimate chemical and physical properties of pears from the electronic nose signal.⁵⁸ The electronic nose could also be a useful and innovative tool to monitor strawberry aroma changes during osmotic dehydration.⁵⁹ A typical nanosensor ‘electronic nose’ can be used for quality control of milk during industrial processing. Nanotechnology-based electronic nose applications include: monitoring and control (for example, direct measuring of specific stages of a process, such as baking); more accurate volatiles measurement than measuring temperature and the time taken currently in baking to monitor product quality, quality assurance (eg, timely warning in a refrigerated environment on whether a ham is no longer safe to eat). Nanosensors are integrated in food packaging to show if the food product is still fit for human consumption. Nanosensors have been developed for food safety and quality control in the European project GOODFOOD (2004–2007) and Nanosieves can be used for filtration of beer or of milk for cheese production.⁶⁰ Nanofiber of microbial cellulose produced by fermentation was also studied to develop novel nanostructured materials.⁶¹

Detection and characterization of nano delivery systems are an essential part of understanding the benefits, as well as the potential toxicity of these systems, in food. Scientists showed that for a sufficient characterization, the nano delivery systems need to be separated from the food matrix, for which high-performance liquid chromatography or field flow fractionation are the most promising techniques. Subsequently, online photon correlation spectroscopy and mass spectrometry proved a convenient combination of techniques to characterize a wide variety of nano delivery systems.⁶² The detection and characteristics of engineered nanoparticles in food has been reported.^63,64 A rapid and cost-effective method has been reported that simultaneously detects three food-borne pathogenic bacteria, Salmonella typhimurium, Shigella flexneri, and E. coli O157:H7, via an approach that combines magnetic microparticles for the enrichment and antibody-conjugated semiconductor quantum dots as fluorescence markers.⁶⁵ Nanosensors can detect allergen proteins to prevent adverse reactions to foods, such as peanuts, tree nuts, and gluten.⁶⁶

Nanofood

The term ‘nanofood’ describes food that has been cultivated, produced, processed or packaged using nanotechnology techniques or tools, or to which manufactured nanomaterials have been added.⁶⁷ Nanofood has, in fact, been part of food processing for centuries, since many food structures naturally exist at the nanoscale. The purpose of nanofood is to improve food safety, enhance nutrition and flavor, and cut costs. Although nanofood is still in its infancy, nanoparticles are now finding application as a carrier of antimicrobial polypeptides required against microbial deterioration of food quality in the food industry. A coating of starch colloids filled with antimicrobial substance, such that if microorganisms grow on the packaged food they will penetrate the starch releasing the antimicrobial agent.⁶⁸ Reports on nanofoods are covered by the popular media. The benefits of nanofood, for instance, include health-promoting additives, longer shelf-lives or new flavor varieties. The current nanotechnology applications in food science provide the detection of food pathogens, through nanosensors that are quick, sensitive and less labor-intensive procedures. However, it is well known that the nanoparticles equipped with new chemical and physical properties that vary from normal macro particles of the same composition may interact with the living systems thereby causing unexpected toxicity.⁶⁹ So far, warnings about nanofoods–products made via the manipulation of molecules–have not reached a tipping point in terms of public attention. Untested nanotechnology is being used in more than 100 food products, food packaging and contact materials currently on the shelf, without warning or new FDA testing.⁷⁰ A list of food products currently containing nanoproducts include: Canola Active Oil (Shemen, Haifa, Israel), Nanotea (Shenzhen Become Industry Trading Co. Guangdong, China), Fortified Fruit Juice (High Vive.com, USA), Nanoceuticals Slim Shake (assorted flavors, RBC Lifesciences, Irving, USA), NanoSlim beverage(NanoSlim), Oat Nutritional Drink (assorted flavors, Toddler Health, Los Angeles, USA), and ‘Daily Vitamin Boost’ fortified fruit juice (Jamba Juice Hawaii, USA) and nanocapsules containing tuna fish oil (a source of omega 3 fatty acids) in “Tip-Top” Up bread (Enfield, Australia).⁷¹ A listing of nanorelated food and beverage is provided by the Nanotech Project in its Nanotechnology Consumer Products Inventory.⁷² ɛ-Polylysine, a food-grade polypeptide, can be added to the oil droplets to help protect from oxidation. Polylysine is much smaller than the phytoglycogen octenyl succinate nanoparticles, allowing it to fill in the gaps between phytoglycogen octenyl succinate nanoparticles.⁷³

Nanoencapsulation

Nanoencapsulation is defined as a technology to pack substances in miniature making use of techniques such as nanocomposite, nanoemulsification, and nanoestructuration and provides final product functionality that includes controlled release of the core. The protection of bioactive compounds, such as vitamins, antioxidants, proteins, and lipids as well as carbohydrates may be achieved using this technique for the production of functional foods with enhanced functionality and stability. The different techniques developed for the production of nanocapsules have been reported along with examples of their application.⁷⁴ Scientists have developed a novel patented technology that has the ability to nanoencapsulate a multitude of bioactive and active ingredients in nutraceutical products. These nanocapsules were found to break down and were absorbed as common foods after they have delivered their active ingredients.⁷⁵ The recent innovation in encapsulation and controlled release technologies, as well as a design principle of novel food delivery systems has been reported.⁷⁶ Nanoencapsulation can make significant savings for formulators, as it can reduce the amount of active ingredients needed.

Researchers examined the encapsulation and controlled release of active food ingredients using nanotechnological approaches.⁷⁷ Octenyl succinic anhydride-ɛ-polylysine has the potential to become bifunctional molecules that can be used as either surfactants or emulsifiers in the encapsulation of nutraceuticals or drugs or as antimicrobial agents.⁷⁸ Hydrophobically modified starch formed micelles encapsulated curcumin.⁷⁹

Lipid-based nanoencapsulation systems enhance the performance of antioxidants by improving their solubility and bioavailability, in vitro and in vivo stability, and preventing their unwanted interactions with other food components. The main lipid-based nanoencapsulation systems that can be used for the protection and delivery of foods and nutraceuticals are nanoliposomes, nanocochleates, and archaeosomes. Nanoliposome technology presents exciting opportunities for food technologists in areas such as encapsulation and controlled release of food materials, as well as the enhanced bioavailability, stability, and shelf-life of sensitive ingredients. The application of nanoliposomes as carrier vehicles of nutrients, nutraceuticals, enzymes, food additives, and food antimicrobials was reported.⁸⁰

Coenzyme Q₁₀ nanoliposomes were produced with the desired encapsulation quality and stability.⁸¹ Colloidosomes are minute capsules made of particles one tenth the size of a human cell and assemble themselves into a hollow shell. Molecules of any substance can be placed inside this shell. Scientists believe that fat blockers, medicine, and vitamins could be placed into the colloidosomes.⁸² A method was proposed to form water-soluble nanoparticles with entrapped β-carotene of controlled functionality.⁸³ Scientists formulated beta-carotene within a nanostructured lipid carrier that allows the normally hydrophobic beta-carotene to be easily dispersed and stabilized in beverages.⁸⁴

Nanoencapsulation technologies have the potential to meet food industry challenges concerning the effective delivery of health functional ingredients and controlled release of flavor compounds. Zein, the prolamine in corn endosperm binds and enrobes lipids, keeping them from deteriorative changes. Further, zein has been shown to adsorb fatty acids and produce periodic structures, most interestingly, nanoscale layers of cooperatively assembled fatty acid and zein sheets.⁸⁵ Soy lecithin is the main structural ingredient in the formation of aqueous nanodispersions that carry high loads of water-insoluble actives. These actives include water-insoluble nutraceuticals, fat-soluble vitamins, and flavors. The encapsulated actives disperse easily into water-based products, showing improved stability and increased bioavailability. A separate study has shown a seven-fold increase in intestinal cell uptake of CoQ₁₀ in nanodispersions versus traditional powder formulations.⁸⁶

A 30 nm spherical product, called NovaSOL, containing two nutrients to burn fat has been developed by German based company Aquanova (Darmstadt, Germany).⁸⁷ Nanocochleates consists of a purified soy based phospholipid that contains at least about 75% by weight of lipid that can be phosphotidyl serine, dioleoylphosphatidylserine, phosphatidic acid, phosphatidylinositol, phosphatidyl glycerol and/or a mixture of one or more of these lipids with other lipids. Additionally or alternatively, the lipid can include phosphatidylcholine, phosphatidylethanolamine, diphosphotidylglycerol, dioleoyl phosphatidic acid, distearoyl phosphatidylserine, dimyristoyl phosphatidylserine, and dipalmitoyl phosphatidylgycerol. Nanocochleates are nanocoiled particles that wrap around micronutrients and have the ability to stabilize and protect an extended range of micronutrients and the potential to increase the nutritional value of processed foods.⁸⁸

Nanoencapsulation of probiotics

Probiotics are generally defined as live mixtures of bacterial species and can be incorporated in foods in the form of yoghurts and yoghurt-type fermented milk, cheese, puddings and fruit based drinks. Encapsulated forms of ingredients achieve longer shelf life of the product. Nanoencapsulation is desirable to develop designer probiotic bacterial preparations that could be delivered to certain parts of the gastro-intestinal tract where they interact with specific receptors. These nanoencapsulated designer probiotic bacterial preparations may act as de novo vaccines, with the capability of modulating immune responses.⁸⁹ Biopolymer assemblies stabilized by various types of noncovalent forces have recently shown considerable progress.⁹⁰

A starch-like nanoparticle can help stop lipids from oxidizing and therefore improve the stability of oil-in-water emulsions.⁹¹ The health benefits of curcumin, the natural pigment that gives the spice turmeric its yellow colour, could be enhanced by encapsulation in nanoemulsions.⁹² The health promotion properties of polyphenols have attracted a lot of attention in recent years. Nanoemulsions could improve stability and oral bioavailability of epigallocatechin gallate and curcumin.⁹³ A stearin-rich milk fraction was used, alone or in combination with α-tocopherol, for the preparation of oil-in-water sodium caseinate-stabilized nanoemulsions. Immobilization of α-tocopherol in fat droplets, composed by high melting temperature milk fat triglycerides, provided protection against degradation.⁹⁴

Nanocomposites in food packaging

Nanotechnology has the potential to generate new food packaging. Nanocomposites can improve mechanical strength; reduce weight; increase heat resistance; and improve barrier against oxygen, carbon dioxide, ultraviolet radiation, moisture, and volatiles of food package materials. The main kinds of nanoparticles have been studied for use in food packaging systems; as well, their effects and applications were overviewed.^95,96 Fine nanoparticulates (100 nm or less) are incorporated into plastics to improve the properties over those of conventional counterparts. Polymer nanocomposites are thermoplastic polymers that have nanoscale inclusions, 2%–8% by weight. Nanoscale inclusions consist of nanoclays, carbon nanoparticles, nanoscale metals and oxides, and polymeric resins. Nanocomposites are characterized by extremely high surface-to-volume ratio, making them highly reactive in comparison to their macroscale counterparts, and thus presenting fundamentally different properties.⁹⁷ Food and beverage packaging comprises 55% to 65% of the $130 billion value of packaging in the United States.⁹⁸ Moreover, nanocomposites could also be characterized by an antimicrobial activity.⁹⁹ Packaging containing nanosensors are coming to food stores to give information of enzymes produced in the breakdown of food molecules making them unsafe for human consumption. The packages could also be used to let air and other enzymes out but not in, thus increasing shelf life, as well as the reduction of man-made preservatives in our foods. Another important potential application of nanoparticles in food packaging is the degradation of ripening gas, such as ethylene.^100,101 In view of the above, the idea to insert active nanoparticles into polymer matrices could bring the twofold advantage to improve the performance of food packaging material and to impart it an additional functionality (antimicrobial, antioxidant, scavenger), thus promoting the prolongation of the shelf life of the packaged product.¹⁰² Researchers reported the challenges of using nanotechnology to create low-cost packaging that assists in functionality, weight, and ease of processing.¹⁰³ The new hybrid plastic, comprising polyamide and layered silicate barriers, makes it much more difficult for oxygen to pass through to the packaged goods than does conventional films made of polyamide. Durethan, from Bayer Polymers (Pittsburg, USA) is a nanocomposite film enriched with an enormous number of silicate nanoparticles that reduce entry of oxygen and other gases and the exit of moisture, thus preventing food from spoiling.¹⁰⁴ Nanocor (Arlington Heights, USA) has developed nanocrystals to be used in nanocomposite plastic beer bottles. This material minimizes loss of carbon dioxide and entry of oxygen into beer bottles.¹⁰⁴ Natural biopolymer-based nanocomposite packaging materials with bio-functional properties have a huge potential for application in the active food packaging industry. Recent advances in the preparation of natural biopolymer-based films and their nanocomposites, and their potential use in packaging applications were reported.¹⁰⁵ The other improvements in nanotechnology for food packaging include carbon nanotubes that can be used in food packaging to improve its mechanical properties. It has been recently discovered that they might exhibit powerful antimicrobial effects. E. coli bacteria died on immediate direct contact with aggregates of carbon nanotubes.¹⁰⁶ Polymer-clay nanocomposite has emerged as a novel food packaging material due to benefits, such as enhanced mechanical, thermal, and barrier properties. Scientists have discussed the potential use of these polymer composites as novel food packaging materials with emphasis on preparation, characterization, properties, recent developments and future prospects.¹⁰⁷ More flexible packaging methods will provide the consumers with fresher and customized products.¹⁰⁸ Nano wheels, nanofibers and nanotubes are being investigated as a means to improve the properties of food packages.¹⁰⁹ Nanotechnology has the potential to influence the packaging sector by delaying oxidation and controlling moisture migration, microbial growth, respiration rates, and volatile flavors and aromas.¹¹⁰ A methodology used to produce polymer nanocomposites with low-cost fibrous materials similar to expensive carbon nanotubes exhibiting optimized dispersion, interfacial bonding, and attractive physical and other properties has been reported.¹¹¹ Chitosan-based nanocomposite films, especially silver-containing ones, showed a promising range of antimicrobial activity.¹¹² PEG coating nanoparticles loaded with garlic essential oil could be used to control the store-product pests.¹¹³ Phytoglycogen octenyl succinate nanoparticles with ɛ-polylysine significantly increased the shelf life of the product. Here, the nanoparticle created a stronger defense against oxygen, free radical and metal ions that cause lipid oxidation.¹¹⁴ Researchers are using silicate nanoparticles to provide a barrier to gasses (for example oxygen), or moisture in a plastic film used for packaging. This could reduce the possibly of food spoiling or drying out.¹¹⁵

Coatings containing nanoparticles

The coatings have been reported to be very efficient at keeping out oxygen and retaining carbon dioxide and can rival traditional active packaging technologies such as oxygen scavengers.¹¹⁶ Examples include a nanocoating, which is an aqueous-based nanocomposite barrier coating, that provides an oxygen barrier with a 1–2 micron coating for food packaging use, and plasma arc deposition of amorphous carbon inside PET bottles as a gas barrier.

Nanoemulsions

Nanoemulsions have been developed for use in the decontamination of food packaging equipment and in the packaging of food. A typical example is a nanomicelle-based product claimed to contain natural glycerin. It removes pesticide residues from fruits and vegetables, as well as the oil/dirt from cutlery. Nanoemulsions have recently received a lot of attention from the food industry due to their high clarity. These enable the addition of nanoemulsified bioactives and flavors to a beverage without a change in product appearance. Nanoemulsions are effective against a variety of food pathogens, including Gram-negative bacteria. They can be used for surface decontamination of food processing plants and for reduction of surface contamination of chicken skin. The growth of Salmonella typhimurium colonies has been eliminated by treatment with nanoemulsion.¹¹⁷ Based on the physicochemical properties of the microencapsulated fish oil, sugar beet pectin must be considered as an alternative to milk proteins and gum Arabic for the encapsulation of functional food ingredients.^118,119 The nanoemulsions showed great promise for use in beverage and other applications.¹²⁰ Various types of nanoemulsion, including single-layer, double-layers and triple-layers nanoemulsions, could be produced, depending on the polyelectrolytes, such as alginate and chitosan.¹²¹ Solid lipid nanoparticles are formed by controlled crystallization of food nanoemulsions and have been reported for delivery of bioactives, such as lycopene and carotenoids.^122,123 The major advantages of solid lipid nanoparticles include large-scale production without the use of organic solvents, high concentration of functional compounds in the system, long term stability, and the ability to be spray dried into powder form. Megestrol acetate oral suspension (MAOS) is an appetite stimulant indicated for cachexia in patients with AIDS. It is available in its original formulation, Megace® (MAOS), and as a nanocrystal dispersion, Megace® ES (MA-ES) (Bristol-Myers Squibb, New York, USA). Bioavailability and absorption were found to be greater for MA-ES than MAOS in fasting subjects, thereby, suggesting MA-ES e a preferred formulation of megestrol acetate when managing cachectic patients whose caloric intake is reduced.¹²⁴

Polymeric nanoparticles

Polymeric nanoparticles for controlled release and targeted delivery of functional compounds have been reported.^125,126 They are made using polymers and surfactants and include alginic acid, polylactic-co-glycolic acid, and chitosan. Further, scientists reported data on polymeric nanoparticles, including vitamin E, itraconazole (an antimicrobial), and beta-carotene as a colorant.^127,128 Biopolymer nanoparticles are highly bioactive solid particles with diameters of 100 nm or less. Weiss and his colleagues have demonstrated that the particles can also serve as carriers of antimicrobial components, with niacin-containing biopolymeric nanoparticles exhibiting much more potent activity against E. coli O157:H7 than particles without nicin.² The discovery of antimicrobial properties of nanozinc oxide and nanomagnesium oxide at the University of Leeds may provide more affordable materials for such applications in food packaging.¹²⁹ Recently, nanoscale processing has been used to make new solidstate forms of food materials, such as cereals. Compared to conventional materials, these materials have new physicochemical properties, such as altered solubility, cohesiveness, stability, and reactivity.¹³⁰

Nanosized self-assembled liquid structures

Nanosized Self-assembled Liquid Structures related to the nanosized vehicles are used as vehicles to targeted nutraceuticals. The vehicles are expanded micelles in the size of ~30 nm and can be used in “clear” beverages without phase separation. They are coined fortifying nanovehicles. Their potential applications include lycopene, beta-carotene, CoQ₁₀, omega-3 fatty acids, phytosterols, and isoflavones.^131–132

Delivering bioactive compounds

Researchers reported iron- and iron/zinc-containing nanostructured compounds for nutritional applications that improved bioavailability and minimize color changes in finished products.¹³³ Scientists have reported different ways to fabricate nanoparticles in the unique range that is suitable for the food and drug delivery system. Synthetic protein nanostructure acts as surrogate mimics, such as viruses and plasmid for food and drug delivery system. The benefits of protein nanoparticles include nontoxicity stability for long duration, nonantigenicity and biodegradability.¹³⁴

Bionanotechnology in food industry

Bionanotechnology is a highly interdisciplinary field that results from the convergence of the physical and life sciences, and engineering. Biosensors and lab-on-a-chip systems are typical outcomes of bionanotechnology research. Bionanotechnology is aimed to bridge the gap between bio- and nano technology, and tries to find the basic principles underlying biological phenomena, as well as the design of tools for accurate control of matter at the nanoscale.¹³⁵ Wageningen BioNT centre (Wageningen, The Netherlands) helps companies utilize the opportunities of micro- and nanotechnology to improve our food and prevent health problems.¹³⁶ Consumers have largely grown to accept nanotechnology in nutrition for packaging and to a lesser extent, even the food itself. This is according to a study from ETH Zurich’s Institute for Environmental Decisions (Zurich, Switzerland).¹³⁷ Ecology Coatings, Inc. (Auburn Hills, USA) has developed UV-cured coatings specifically to address opportunities within the paper and packaging industry. These coatings offer significant benefits over existing UV-cured coatings, and replace expensive adhesive-plastic lamination used in many label applications. This reduces the cost of materials and simplifies the manufacturing line.¹³⁸

Smart food packaging

Smart packaging responds to environmental conditions or repairs it or alert a consumer to contamination and/or the presence of pathogens. Chemical giant Bayer (Leverkusen, Germany) produces a transparent plastic film (called Durethan) containing nanoparticles of clay. The nanoparticles are dispersed throughout the plastic and are able to block oxygen, carbon dioxide and moisture from reaching fresh meats or other foods. The nanoclay also makes the plastic lighter, stronger and more heat resistant. Today, Nanocor, a subsidiary of Amcol International Corp. (Hoffman Estates, USA), is producing nanocomposites for use in plastic beer bottles that give the brew a six-month shelf-life. By embedding nanocrystals in plastic, researchers have created a molecular barrier that helps prevent the escape of oxygen. Nanocor and Southern Clay Products (Austin, USA) are now working on a plastic beer bottle that may increase shelf-life to 18 months. Researchers in the Netherlands are going one further to develop intelligent packaging that will release a preservative if the food within begins to spoil. This “release on command” preservative packaging operates by using a bio switch developed through nanotechnology. ‘Smart’ food packaging will warn when oxygen has got inside, or if food is going off. Such packaging is already in use in brewing and dairy production and consists of nanofilters that can filter out micro-organisms and even viruses. In lab experiments, the color has been removed from beetroot juice, leaving the flavor; and red wine turned into white. Lactose can now be filtered from milk, and replaced with another sugar – making all milk suitable for the lactose-intolerant. Nanoceramic particles enable clustering of dirt molecules, thereby; keeping cooking oil fresh and soluble forever bread – Tip-Top – contains undetectable nanocapsules of omega-3 fatty acids.¹³⁹ Vitamin B₁₂ spray can simply be sprayed inside a child’s mouth to absorb the nanosized vitamins directly through the mucal cells, thereby, relieving the need to bribe children to eat fruits and vegetables. Nano-capsules delivered chemicals in rapeseed cooking oil, will stop cholesterol entering the bloodstream. Nano packaging with self cleaning abilities or nanoscale filters will allow the removal of all bacteria from milk or water without boiling.¹⁴⁰ In the area of nanolaminated coatings on the bioavailability of encapsulated lipids, bioactive lipophilic or fat-liking compounds could be incorporated into foods or beverages, which may increase the ingredient’s stability, palatability, desirability, and bioactivity.¹⁴¹ Functionalized nanostructured materials are finding applications in many sectors of the food industry, including novel nanosensors, new packaging materials with improved mechanical and barrier properties, and efficient and targeted nutrient delivery systems. An improved understanding of the benefits and the risks of the technology, based on sound scientific data, will help gain the acceptance of nanotechnology by the food industry. New horizons for nanotechnology in food science may be achieved by further research on nanoscale structures and methods to control interactions between single molecules.¹⁴² Advances in processes for producing nanostructured materials coupled with appropriate formulation strategies have enabled the production and stabilization of nanoparticles that have potential applications in the food and related industries.^143,144 The food processing industry should ensure consumer confidence and acceptance of nanofoods. Scientists are not yet certain how various nanomaterials will behave when they cross membranes, such as the blood-brain barrier, or when they are inhaled during production. The safety of a given compound in a food should not automatically apply to a nanoversion of the compound due to possible novel properties and characteristics. Insufficient scientific data prevents FDA from extending GRAS (generally recognized as safe) status of an ingredient to its nanosized version. A significant segment of the public does not want its food “engineered” – bio, nano, GM or otherwise.¹⁴⁵

Probiotics in food nanotechnology

Probiotics are products aimed at delivering living, potentially beneficial, bacterial cells to the gut ecosystem of humans and other animals. Calcium and Dr Kim’s probiotic nanofood combination reduces risk of osteoporosis. Probiotic-containing foods are the best way to get Dr Kim’s probiotic nanofood for most people. A variety of capsules, liquids, and powders are available. Powders can be stirred into food but should not be added to food warmer than room temperature, because heat will kill the bacteria. Another option is to add to your diet. These foods include yogurt, kefir (a cultured-milk beverage), tempeh (made from soybeans), and kimchi (a Korean fermented cabbage dish).¹⁴⁶

Edible nanocoatings

Nanotechnology is enabling the development of nanoscale edible coatings as thin as 5 nm. Edible nanocoatings could be used on meats, cheese, fruit and vegetables, confectionery, bakery goods, and fast food and could provide a barrier to moisture and gas exchange, act as a vehicle to deliver colors, flavors, antioxidants, enzymes and antibrowning agents, and could also increase the shelf life of manufactured foods, even after the packaging is opened.¹⁴⁷ The properties of mango puree edible films can be significantly improved through cellulose nanofibers reinforcement.¹⁴⁸ An edible antibacterial nanocoating can be applied directly to bakery goods.¹⁴⁹

Regulation of nanotechnology in the food industry

Despite rapid developments in food nanotechnology, little is known about the occurrence, fate, and toxicity of nanoparticles. Nanotechnology-derived food ingredients, food additives and food contact materials have been reported in relation to potential implications for consumer safety and regulatory controls.^135,150 A significant segment of the public does not want its food “engineered” – bio, nano, genetically modified or otherwise.¹⁵¹ Regulatory bodies around the world have established rules and guiding principles for nanoscale materials that have ramifications for use in food. Uncertainty exists over the regulation of nano-based products and is linked in part due to a lack of necessary safety data needed to inform regulatory bodies.¹⁵² Efforts to facilitate international collaboration and information exchange are underway to ensure acceptance and utilization of the many benefits of nanotechnology¹⁵³ Thus, agencies worldwide are gathering information in an effort to decide how best to proceed.¹⁵⁴ There is an urgent need for specific guidelines for testing of nanofoods.¹⁵⁵ The importance of naturalness in food products and trust were significant factors influencing the perceived risk and the perceived benefit of nanotechnology foods and nanotechnology food packaging.¹⁵⁶ UK Soil Association (Bristol, UK) reported that their revised organic standard would prohibit products and processes derived from nanotechnologies (200 nm or smaller).¹⁵⁷ The current risk assessment approach used by FAO/WHO and Codex is available and appears suitable for ENMs in food.²³ However, there is a need to consider the whole life cycle of engineered nanomaterials in agrifood applications.

Conclusions and perspectives

Nanotechnology has the potential to improve foods, making them tastier, healthier, and more nutritious, to generate new food products, new food packaging, and storage. However, many of the applications are currently at an elementary stage, and most are aimed at high-value products, at least in the short term. Successful applications of nanotechnology to foods are limited. Nanotechnology can be used to enhance food flavor and texture, to reduce fat content, or to encapsulate nutrients, such as vitamins, to ensure they do not degrade during a product’s shelf life. In addition to this, nanomaterials can be used to make packaging that keeps the product inside fresher for longer. Intelligent food packaging, incorporating nanosensors, could even provide consumers with information on the state of the food inside.

Food packages are embedded with nanoparticles that alert consumers when a product is no longer safe to eat. Sensors can warn before the food goes rotten or can inform us the exact nutritional status contained in the contents. In fact, nanotechnology is going to change the fabrication of the entire packaging industry.

Food nanotechnology advances offers important challenges for both government and industry. The food processing industry must ensure consumer confidence and acceptance of nanofoods. Regulatory bodies, such as FDA, should author guidance with respect to the criteria to be followed in evaluating the safety of food, food packaging, and supplement uses of nanomaterials with novel properties.

It is important to note that nanofoods originate in the laboratory, hence are not the same thing as conventional nanofoods. There has been insufficient scientific exploration of naturally occurring nanosystems and the benefits they provide. Thus, it is very difficult to make broad generalizations as to whether nanotechnology is good or bad. However, nanotechnology food packaging was assessed as less problematic than nanotechnology foods. Moreover, nanofoods are not labeled as such, and consumers who wish to avoid these food products are not being given this option. Thus, mandatory testing of nanomodified foods is desirable before they are allowed on the market. New approaches and standardized test procedures to study the impact of nanoparticles on living cells are urgently needed for the evaluation of potential hazards relating to human exposure to nanoparticles. It is widely expected that nanotechnology-derived food products will be available increasingly to consumers worldwide in the coming years.