CHAPTER21 21 -FoodNanotechnology:CurrentDevelopmentsandFutureProspectsCarmenMoraru,QingrongHuang,PaulTakhistov,HulyaDogan,andJozefKokiniContentsI. Introduction 370II. The Potential of Nanotechnology for the Food and Agricultural System371III. CharacterizationandManipulationofFoodBiomoleculesattheNanoscale 372III.A. Instrumentationforstudyingnanoscalepropertiesoffoodandbiopolymersystems 372III.B. Investigationoffoodbiopolymerpropertiesusingthetoolsofnanotechnology 376IV. DevelopmentofNovel Nano-StructuresforFoodApplications 379IV.A. Manipulation of molecules at nanoscale for improved processing 379IV.B. Nanotubesandhighsurfaceareananomaterials 380IV.C. Nanodeliverysystems 382V. NanotoolsforFoodandBio-Safety 390VI. ProspectsandChallengesfortheFuture 392References 394AbstractNanotechnology, one of themost promisingscientificfields of research indecades, is thescienceandtechnology that has enabledthestudy ofphenomenaatthenanometerscaleandthemanipulationofmaterialsatmacromolecular, molecular, and atomic scales. The unusual propertiesdisplayedbymaterialsinthenanometer rangeprovideground-breakingscientific, technological, andcommercial opportunities. Usingthetoolsofnanotechnology, it is nowpossibletostudy thebehavior of individualmoleculesandtheinteractionsinwhichtheyparticipate, andusetheseinteractions to improve the functionality of synthetic or biological materials.Nanotechnology has the potential to revolutionize the global foodand agricultural system. Nanoscale control of food molecules couldallowthe modification of macroscale characteristics of foods such asprocessability, texture, sensoryattributes, andshelflife. Itisexpectedthatnanotechnology will facilitate the development of lighter and moreIUFoSTWorldCongressBook:Global IssuesinFoodScienceandTechnology ISBN97801237412402009ElsevierInc. All rightsreserved.369precise food manufacturing equipment, novel packaging materials, as wellas non-polluting, cheaper,and more efficient food-processing techniques.The food industry is currently trying to identify opportunities to use themost promising discoveries of nanotechnology to improve food processingandfoodproducts. Aswithanynewtechnology, aseriesofchallengesisforeseen. Inparticular, the potential dangers causedby the misuse ofnanotechnology should be clearly identified and prevented. Overallthough, itisgenerallyrecognizedthatnanotechnologyhasthepotentialtoenable significant steps for the enhancement of humanlife, partlythrough the improvement of the food and agricultural system.This chapter will provide an up-to-date, comprehensive evaluation of theexisting and upcoming applications and implications of nanotechnology forthe food and agricultural sector.I. INTRODUCTIONNanotechnology, denedbytheBritishStandardsInstitution(BSI)asthedesign,characterization,productionandapplicationofstructures,devicesand systems by controlling shape and size at the nanoscale (BSI, 2005), hasemerged as one of the most promising scientic elds of research in decades.This newarea of science and technologyallows scientists to study phenomenathat occurat thenanometer scaleandtomanipulatematerials at macro-molecular, molecular, and atomic scales, where properties and functionalitiesdiffer signicantly from those at macroscopic scale. Nanoscale refers to thesize range where one or more dimensions are of the order of 100 nm or less(BSI, 2005).IntheUnitedStates, interest innanotechnologyreceivedabigboostafter theNational NanotechnologyInitiativeidentiedit as anemergingarea of national interest (Srivastava, 2000). The unusual properties displayedbymaterialsat thenanometer-lengthscaleandthedevelopment of tech-nologiescapableofmanipulatingorself-assemblingmaterialsmoleculebymolecule, havesincebeenshowntopotentiallyprovideworld-changingscientific,technological,andcommercialopportunities.The building strategies used in nanotechnology include the top downapproach, in which nano-level structures are generated by breaking up bulkmaterialsthroughmilling, nanolithography, orprecisionengineering; andthe bottom up approach, in which nanostructures are built from individualatoms or molecules capable of self-assembling. The bottom up strategy hasledtothedevelopmentofremarkablystrongmaterialswithpreciselycon-trolled structure and properties, high surface area particles, and materials thatencapsulate active compounds, or smart coatings that are self-cleaning or canchange color depending on environmental conditions. Nanotechnology hasalso opened up new ways for studying individual molecules and specicallythe intra- and inter-molecular interactions in which they participate, and can370 CarmenMoraruetal.improve the complexity and functionality of biological materials. Examplesinclude elucidation of the mechanisms of catalysis and enzymatic reactions,muscular contraction, cellular transport, DNA replication and transcription,DNA unknotting and unwinding, and protein folding and unfolding.Following the rst feature article published on the topic of foodnanotechnology(Moraruetal.,2003),several moreauthorsaddressedthepotential of nanotechnologyinareas suchas foodsafetyandbiosecurity(Baeumner, 2004), nanoscale properties of food materials (Weiss et al., 2006;Leeet al., 2007), andfunctional foodsforhealthpromotion(Chenet al.,2006). This chapter will provide an up-to-date evaluation of the applicationsandimplicationsofnanotechnologyforthefoodandagriculturalsector.II. THEPOTENTIALOFNANOTECHNOLOGYFORTHEFOODANDAGRICULTURALSYSTEMTheprogress madeinrecent years suggests that nanotechnologyhas thepotential to revolutionize the global food and agricultural system. Nanoscalecontrol of food molecules could allow the modication of many macroscalecharacteristics of foods, suchas texture, sensoryattributes, processability,and shelf life. The tools of nanotechnology have already allowed scientists tobetterunderstandthewayinwhichfoodcomponentsarestructured,andhow they interact with each other; it is expected that this understanding willenableamoreprecisemanipulationof foodmolecules for thedesignofhealthier, tastier, and safer foods. Non-polluting, cheaper, and moreefcientprocesseswill likelybedeveloped; lighterandmoreprecisefoodmanufacturing equipment will be built; and smart packaging materials willbedevelopedandusedtosafelypackagewholesome,nutraceutical-loadedfoods. Development of novel deliverymethods andthemanufactureofsensors for pathogen detection are some other useful applications ofnanotechnologyinthefoodsector.Someofthebenetsofnanotechnologywill beconveyedtothefoodsystem directly through agriculture and agricultural research. Newly createdtoolsinmolecularandcellularbiologywill enablesignicantadvancesinreproductivescienceandtechnology,diseaseprevention,andtreatmentofplantsandanimals,potentiallyboostingtheproductionofrawfoodmate-rials, whilethedevelopmentof biosensorsforpathogenandcontaminantdetectioninagricultural products will helpensurethesafetyof thefoodsupply. Conversionofrenewableagricultural materialsorfoodwasteintoenergy and useful byproducts is an environmentally oriented area of researchthatcouldbegreatly enhancedbynanotechnology.FoodNanotechnology: CurrentDevelopmentsandFutureProspects 371Fourmajor target areas in food science and technology are expected tobesignicantlyenhancedbynanotechnology: (1)developmentof mate-rials withnovel functionality, (2) micro- andnanoscale processing, (3)product development, and (4) the design of methods and instrumentationfor foodsafetyandbiosecurity. Amatrixof the applications of nano-technology inthe food industry, grouped by target area, is showninFigure21.1.III. CHARACTERIZATIONANDMANIPULATIONOFFOODBIOMOLECULESATTHENANOSCALEIII.A. InstrumentationforstudyingnanoscalepropertiesoffoodandbiopolymersystemsNanotechnology uses a range of tools to observe, characterize, and controlphenomena at the nanoscale. Scanning probe microscopy (SPM) is a familyof techniques that provides images of surface topography and, in some cases,allows quantication of surface properties down to the molecular or atomicscale. Since the invention ofatomic force microscopy (AFM) and its use instructural biology of nucleic acids, this technique has been intensely used asamicromanipulationresearchtool(Binnigetal.,1986;Vianietal.,2000).Compared to other microscopic methods, AFMhas the advantage ofFigure21.1 Applicationmatrixofnanotechnologyinfoodscienceandtechnology(Moraruetal., 2003).372 CarmenMoraruetal.allowing imaging of non-conducting biomaterials including food materials,isoneofthefirstandmostpopularapplicationsofAFM.AFMoperatesinvariousmodes, allowingamultitudeof applications.When used in the contact mode, AFM can measure properties like stiffness,hardness, friction, elasticity, or adhesion on a surface, down to the molecularlevel. Forcedistance curves can be obtained by extending the AFMcantilever tip down to the surface of a sample, making contact between thetipandthesamplesurface,followedbyretractingthetipfromthesurface(Figure21.2). Theslopeof theforcedeformationcurvecanbeusedasa measureof themodulus of elasticityat thesamplesurface. Thenon-contact and intermittent contact modes of AFM are used when a probabilityof damaging the sample surface exists due to the contact with the cantilever.Inthe intermittent contact mode, the tipof the cantilever oscillates ataresonantfrequency andtapsthesamplesurfacelightlyduringeachoscil-lation cycle. The decrease in oscillation amplitude occurring when the tip isbrought closer to the sample is used as a feedback parameter to build surfacemorphology. The tapping mode of AFMcan be used for structuralinvestigationof delicate biopolymer structures, suchas hylan(Cowmanetal.,2000)orxanthangum(CamesanoandWilkinson,2001).Thenon-contact modeis alsoveryuseful inimagingisolatedbiomacromoleculesorsupramolecularassemblies,sinceitisabletoavoidsampledisruptionortipcontamination; several non-contact studies have beenperformedonfoodbiomacromolecules suchas xanthangum, k-carageenan, gellan, andcollagen(McIntireandBrant,1997).SomeAFMmeasurements employthecolloidal probetechnique, inwhichthetipof thecantilever is chemicallymodiedbyattachingsilicabeads functionalizedwithaminogroups, or other molecules toit (HilalApproachRetractAdhesive/Pull-off forceDistance, nmForce, nNAttractiveforceFigure21.2 MeasurementofsurfaceforcesusingAFM.FoodNanotechnology: CurrentDevelopmentsandFutureProspects 373et al., 2002; Sakai et al., 2002). Modification of AFM probe tips by covalentlinkingwithavarietyof functional groups enables thedirect probingofspecificmolecular interactions andimagingwithchemical sensitivity. Inmany cases, the probe tip is u-functionalized withalkyl thiols, whichspontaneouslyformmonolayersthat terminateinwell-definedfunctionalgroups (Figure 21.3). Arange of u-functionalized alkyl thiols is nowcommercially available, including those withmethyl, amine, carboxylicacid,hydroxylandphenylheadgroups(Smithetal.,2003).Byusingprobe tips functionalizedwithhydrophobic or hydrophilicmolecules, Frisbieet al. (1994) showedthat theadhesiveinteractions be-tweensimplehydrophobichydrophobic(-CH3. -CH3), hydrophobichydrophilic (-CH3.-COOH), and hydrophilichydrophilic (-COOH.-COOH) groups could be measured reproducibly. The difference betweentheseadhesiveinteractionscorrelatedwell withthefrictionimagesof thepatterned sample surface, demonstrating that the spatial distribution ofhydrophilic and hydrophobic functional groups can be predictably mappedwithfunctionalizedtips. Examplesof forcedisplacementcurvesrecordedon -CH3 and -COOH surfaces with functionalized probe tips are shown inFigure21.4.Schonherr(1999)determinedthepull-off forcedistributionsbyusingaCOOH-terminatedtipwithself-assembledmonolayers(SAMs)ofocta-decanethiol (COOH-terminated surface) and 11-mercaptoundecanoic acidFigure 21.3 Modification of probe tip with a self-assembly of molecular monolayers.(a) u-functionalized alkyl thiols with functional group (R); (b) formation of monolayers(R group represented by the thick horizontal line); (c) electron micrograph of a typicalAFMprobe; (d)schematicrepresentationoftheAFMprobe(Smithetal., 2003).374 CarmenMoraruetal.(CH3-terminatedsurface) onsputteredgold. Noyet al. (1997) providedimages of apatternedSAMwith10 10mmregions terminatedwith-COOHgroups that repeatedevery30mminaregular pattern. Topo-graphical images failedtoreveal this patternsincethesurfaces exhibitedalmost flat topography across the CH3- and COOH-terminated regions ofthe sample, while the chemical force maps obtained with functionalized tipsreadilyshowedchemicalinformationaboutthesurfaces.ThedevelopmentofnewSPMinstrumentation,suchasthenear-eldscanningopticalmicroscope(NSOM)(Betzigetal.,1991),scanningther-mal microscope(SThM)(Majumdaret al., 1993; Majumdar, 1999), scan-ning capacitance microscope (SCM) (Williams et al., 1989), magnetic forceand resonance microscopes (MFM) (Hobbs et al., 1989; Rugar et al., 1992),and scanning electrochemical microscope (SECM) (Bard et al., 1991),enhancedthecapabilityofSPMinvestigations.AmongtheapplicationsofSPMforanalysisofnanomaterials,asensorthatcanmeasureatomic-levelforces betweentwosurfaces (as theyapproacheachotherandcomeintocontact) has been developed (Houston and Michalske, 1992). Theinterfacial forcemicroscope(IFM), whichutilizesafeedbackforcesensorthateliminatesthesnap-to-contacteventinherentinotherscanningforcemicroscope designs, allows more accurate measurement of the full range ofadhesive interactions; it can also be used to image surfaces. Anotherinstrument,theAtomTracker,canobserveanindividualatominmotionFigure 21.4 Typical forcedisplacement curves recorded for -COOH/-CH3, -CH3/-CH3,and-COOH/-COOHtip-sampleinteractions(Frisbieetal., 1994).FoodNanotechnology: CurrentDevelopmentsandFutureProspects 375andtrackthis motionupto1000times faster thanaconventional STM(Swartzentruber, 1996). Continuousmonitoringof anindividual atominmotionasitbindsto various sitesonasurfaceallowsthediffusingatomtobecomeaprobeofthesurfacestructureanditsproperties.Anentirenewgenerationof analytical instrumentationandnanoscaledevices capable of providinginformation regarding physical, chemical, andmechanical phenomena, includingmaterial properties at nanoscale, willmost likelybedevelopedinthenear future(Takhistov, 2006). As non-destructive,real-timemeasurementsofthepropertiesofnanoparticlesandnanostructured materials evolve, there will be exceptional opportunities forfundamental andappliedinvestigations, as well as problem-solvingat thenanoscale(BrustandKiely,2002;Haruyama,2003;Takhistov,2006).III.B. InvestigationoffoodbiopolymerpropertiesusingthetoolsofnanotechnologyIII.B.1. MolecularstructureAFMhasbeenincreasinglyusedinthelastdecadeforthestructuralchar-acterizationoffoodbiopolymerssuchasstarch(Gallantetal.,1997;Bakeretal.,2001),hydrocolloids(Bakeretal.,1997;McIntireandBrant,1997),andproteins(McMasteretal., 1999gliadinmolecules).AFMimagesofzeinfilmdrop,depositedontoasiliconwaferwithahydrophobiccoating,helped Panchapakesan (2005) visualize the orientation of zein molecules onthesurfaceof thefilm(Figure21.5). Ellipsoidal structures witha meanheightof13.6nmwereobservedonthesurfaceofthespin-castfilms.AFM also enabled the study of rheological properties of single-polymerchains, suchas proteins (Nakajima et al., 2001; Rief andGrubmuller,2002), polysaccharides (dextran, amylose, cellulose) (Rief and Grubmuller,2002), andDNA(Marko, 1997; Clausen-Schaumannet al., 2000; Stricket al., 2000). Nitta et al. (2000) usedAFMtomeasurethelocal elasticFigure 21.5 AFM images of spin-cast zein film with various nanoscale well patterns:(a) 0.1% film of 90% EtOH insoluble zein fraction, (b) 0.01% spin-cast commercial zeinfilm, and(c)0.1%commercial zein(Panchapakesan, 2005).376 CarmenMoraruetal.modulus of agar gels, whichcorrelated well withthe elastic modulusobtainedfromtraditionalrheologicalmeasurements.Most recently, the conformation of bovine serum albumin (BSA) and itsinteractions with negatively charged surfaces in saline solutionsof differentpH were investigated via small-angle neutron scattering (SANS) and AFM-basedchemical forcemicroscopy(CFM) (Li etal.,2008). Inthisstudy, thecontribution of elementary interactions was extracted fromstatisticallyaveragedforceextensioncurves. Acomparisonof theSANSandCFMresults showed that, at pH lower than the isoelectric point (pI) of BSA, boththesizeoftheBSAchainandthestretchableextensionofBSAfragmentsdecreasedwithincreaseofpH.ThissuggestedthatwhentheBSAchainisattractive to the substrate, the change in chain conformation on the surfacepresents similar pH dependence as in bulk solution. However, at pH higherthan thepI,theconformation changeof theBSAchain inbulksolutionisopposite to that of BSA fragments on the surface. Such an approach could beextendedtothestudy ofinteractionsbetween variousfoodcomponentsatnanoscale.III.B.2. BiopolymertransitionsThedevelopmentofnanomaterialsrequiresagoodunderstandingoftheirreactions to stress, strain, temperature, plasticizers, and aging at themolecular and atomic levels. For nanostructured materials, it is important tobe able to characterize the local properties of the matrix, which is extremelydifcult, especiallywheninteractions betweenthedifferent phases occur(Ouleveyetal.,1998).The ability to manipulate individual biomolecules using AFM has madeit possible to study their structural transitions and action mechanisms (Stricket al., 2000). Atomic and friction force microscopy has been used by variousresearchers for measuringlocal glass transition, andnanorheological andnanotribological propertiesofpolymers(Teradaetal.,2000;Morrisetal.,2001;Nakajima etal., 2001;Boskovic etal., 2002).One drawback insuchmeasurements is the significant friction that occurs in the system, hinderingtheaccuracy ofthedata.Toovercomethisproblem,Ouleveyetal.(1998)developed a technique able to probe the properties of the submicron phasesof inhomogeneous materials, calledvariable-temperaturescanninglocal-accelerationmicroscopy (T-SLAM). This is the nanoscale equivalent ofDMTA,andgivesinformationrelatedtotheinternalfrictionandthevar-iations of the dynamic modulus of nanometer-sizedvolumes. ByusingT-SLAM,itispossibletostudythedefectdynamicsinnanomaterialsandcomposites, to thus determine primary and secondary relaxations as well asviscoplasticity (Ouleveyet al., 1998). Micro-thermal analysis is anotherFoodNanotechnology: CurrentDevelopmentsandFutureProspects 377technique that has generated considerable interest in the polymer andpharmaceuticalindustries,andcanprovidesimilarinformation.Non-intrusivedeterminationof thelocal phasebehavior is extremelyvaluablefor understandingthemiscibilityof foodbiopolymers. Thede-velopment of the above-mentioned techniques facilitates such studies,whichcouldultimatelyleadtoimprovedcontrolanddesignofthequalityandstability offoods.III.B.3. IntermolecularinteractionsMost biological processes, such as DNA replication, protein synthesis, druginteraction, as well as interactions between biomolecules, are largelygovernedbyintermolecular forces andcanalsobemeasuredwithAFM(Willemsen et al., 2000; Strick et al., 2001; Rief and Grubmuller, 2002). BycombiningSPMandAFMwithotherimaging, mechanical,andspectro-scopic methods, it is nowpossible to quantitatively characterize thestructuresof polymers at themicronandnanometerlevels, aswell astheintra-andinter-molecularforcesstabilizingsuchstructures.Aresearch group fromThe Technical University of Munich measured thestrength of the chemical bond between a water-soluble vitamin (biotin) anda protein (streptavidin) (Florin et al., 1994). Macromolecular adsorption andinteractionsattheliquidliquidinterfaceareofconsiderableimportanceinfood processing. Detailed studies of the distribution and interactions of sur-factants at interfaces in emulsions and micro-emulsions have become possibledue to the development of in-situ techniques such as AFM and total internalreflection fluorescence microscopy (TIRFM) (Gajraj and Ofoli, 2000).The gelation ability, the mechanisms of gelation, and the microstructureof theresultinggels werestudiedfor biopolymers suchas k-carageenan(Ikeda et al., 2001) and xanthan gum (Morris et al., 2001). Gajraj and Ofoli(2000) visualized protein networks by AFM and showed that their resistanceto fracture determines the interfacial stability. The non-covalent interactionsofthehigh-molecular-weight(HMW)subunitsofwheatglutenin,whichplay an important role in the viscoelasticity of wheat flour dough, were alsoinvestigatedusingAFM(Humphrisetal.,2000).AFMhas alsobeenprovenuseful instudyingtheadsorptionof smallparticles and biological molecules from an aqueous uid onto a solid surface(Hilal et al., 2002). This couldleadtoabetter understandingof mineralfouling of food-processing equipment. Mineral deposits are a seriousprobleminheat exchangers usedtopasteurizeliquidfoods (i.e. milkorbeverages), sincesuchdepositshinder theheat transfer, leadingtohigherenergyconsumption, difficulties incleaning, as well as reducedproductqualityandsafetyproblems. Agoodunderstandingof factors controllingfoulingof suchsurfaces couldfacilitatethedesignof heat exchangers to378 CarmenMoraruetal.minimizetheformationof mineral deposits andtoalloweasiercleaning,whichwouldaidtheprocessingofliquidfoodssignificantly.Thein-depthstudyof membrane fouling inmembrane separationprocesses, suchasmicrofiltrationandultrafiltration, has alsobeenapproachedusingAFM(Jamesetal.,2003).IV. DEVELOPMENTOFNOVELNANO-STRUCTURESFORFOODAPPLICATIONSNanotechnology has provided unprecedented opportunities for thedevelopment of novel nanomaterials and the investigation of their propertiesat the nanoscale. Nanomaterials canbefoundinnature, suchas nano-particles existing insoil (clays, zeolites, imogolite, iron, andmanganeseoxides), but they can also be created through nanotechnology itself(Takhistov,2006).Nanostructuredmaterialsexhibituniquepropertiesthatopenwindowsof opportunityforthecreationofnew, high-performancematerials that will have a critical impact on food manufacturing, packaging,andstorage. Someexamples of hownanomaterials canbeusedinfoodapplicationswillbediscussedinthefollowingsection.IV.A. ManipulationofmoleculesatnanoscaleforimprovedprocessingFreezingisoneof thebestmethodsknownforfoodpreservation. Whenproperly processed, packaged,andstored,frozenfoodscomeclosetofreshfoods in terms of nutrition, color, avor, and texture; however, temperatureuctuationsinthefrozenproductmaycausethefreewatertoexperienceseveral cyclesoficeformationandmelting. Thiscanleadtoanumberofundesirableeffects, includingmoisturemigration, dehydration, structuralbreakdown, and formation of large ice crystals, imparting a gritty mouthfeeluponconsumptionoftheproduct.Byusingpuriedextracellularicenu-cleators(ECIN),icenucleationtemperaturescanbeelevated,whichpro-motes freezingandreducedfreezingtimeandleads tosignicant energysavings (Li andLee, 1995; ZasypkinandLee, 1999). Recently, Huang(current author) andassociates at Rutgers University developeda newprocessingmethodthatformsananoscaleECINcoatingonthesurfaceofpolymer films byusingthelayer-by-layer (LbL) approach. LbLis widelyused in the construction of multilayer films of polyelectrolytes for formationof two-dimensional structures on flat substrates. With suitable control of thechargedensity ofthepolyelectrolytesolution,itispossibletodramaticallymanipulatethemolecularorganization,surfacemorphology,andmechan-ical properties of the multilayer films (Decher, 1997). Lin et al. (2008) usedthe quartz crystal microbalance withdissipationmonitoring (QCM-D)FoodNanotechnology: CurrentDevelopmentsandFutureProspects 379technique tomonitor (in-situ) the multilayer formationof poly(diallyl-dimethylammoniumchloride) (PDDA)/kappa-carrageenan. The surfacemorphology ofthemultilayer filmsbyPDDA withkappa-carrageenanandiota-carrageenanwasimagedbyusingAFMinthetappingmode, whichindicated that the surface morphology of the final polysaccharide multilayerfilmdepends on the conformation of the polysaccharides in solutionduring the multilayer buildup. Furthermore, the same group of researcherssuccessfully prepared ECINnano-coating on the carrageenan/PDDAmultilayer polymer film surface. Preliminary results indicated that the wateron the multilayer film surfaces containing ECIN was frozen, while the wateronthesamesurfaceswithout ECINremainedinliquidform, suggestingthattheECINnano-coatingstillmaintainedicenucleationactivity.Nanotechnology tools could also be used to functionalize microltrationor ultraltration polymeric membranes by lling their pores with polymericoroligomericliquidswithanafnityforcompoundsof interest(Jelinski,1999). An AustralianAmerican team of researchers has discoveredananoparticle-enhancedmembranethatcombinesorganicpolymerswithinorganic silica nanoparticles, enabling large molecules to pass through morereadily than smaller molecules (Kingsley, 2002). The addition of silicaresultedinover200%improvementinthefluxandincreasedtheperme-ability of the membrane. The increased permeability was due to thenanoparticles, which, according to the authors, pushed the polymer chainsapart, creatinglargeropeningsinthemembranesstructure. Thereporteduse of such membranes is to purify ethanol and methanol inexpensively, butfood-relatedapplicationscouldalsobecomepossible.These are just a couple of examples of howmanipulation at thenanoscalecouldbeuseddirectlytoenhancefood-processingoperations,andthefuturewillprobablybringaboutamultitudeofsuchexamples.IV.B. NanotubesandhighsurfaceareananomaterialsNanotubes, a relatively new generation of nanomaterials, were discovered in1991bytheJapaneseelectronmicroscopistSumioIijimaofNECCorpo-ration. Nanotubes aremadebywinding singlesheets of graphitewithhoneycombstructuresinto verylong,thintubesthathaveastable,strong,and exible structure. Nanotubes are the strongest bers known today; onenanotube is estimatedtobe 10100times stronger thansteel per unitweight. Researchersaretryingtoexploittheirextraordinarystrengthandexibility, anduse, inmakingnanotube-reinforcedcompositeswithhighfractureandthermalresistance.Suchnewmaterialscouldreplaceconven-tional ceramics, alumina, orevenmetalsinthebuildingof aircraft, gears,380 CarmenMoraruetal.bearings, car parts, medical devices, sports equipment, and industrialfood-processing equipment (Spice, 1999; Gorman, 2003; Zhan et al., 2003).Recent studies suggest the use of carbon nanotubes for biologicalpurposes, suchas crystallizationof proteins, buildingof bioreactors andbiosensors(Huanget al., 2002). However, forbiological applications, theinsolubilityofcarbonnanotubesinaqueousmedianeedstobeovercome.AresearchgroupatUniversity ofCaliforniasolubilizedsingle-wallcarbonnanotubes (SWNT) inaqueous iodinestarchsolutions (Dagani, 2002),whilea researchgroupinIsrael obtaineda similar result usingaqueoussolutionsofgumarabic(Bandyopadhyayaetal.,2002).Othersolutionsforsolubilizationof SWNTconsist of functionalizingthetubeswithglucos-amine (Pompeo and Resasco, 2002) or bovine serum albumin (Huang et al.,2002). Inanotherexample, nanotubesareformedbytheself-assemblyofphospholipid bilayers capable of entrapping active compounds. Due to theirbiocompatibility, suchtubules areideal for deliveryinbiological systems(Jelinski, 1999). Carbon nanotubes, particularly multi-wall nanotubes(MWNT) withwell-defined nanostructures, canalsobe used tobuildsensors.Manufacturing of nanotube membranes is an area with signicantpotential for use in food systems. High-selectivity nanotube membranes canbeusedforanalyticalpurposes,aspartofthesensorsformolecularrecog-nition of enzymes, antibodies, various proteins and DNA, or for themembraneseparationof biomolecules, suchas proteins (LeeandMartin,2002; Rouhi, 2002). The selectivity and yield of membranes currently usedinthefoodindustryarenot fullysatisfactory, mainlyduetothelimitedcontrol of their structure and chemical affinity. By functionalizingnanotubesinadesiredmanner,membranescouldbetailoredtoefficientlyseparate molecules both on the basis of theirmolecularsize and shape, andon their chemical affinity. Lee and Martin (2002) developed membranes thatcontain monodispersegold nanotubes with inside diameters smallerthan 1nm; such membranes can be used either forthe separation of molecules orfor the transport of ions. The same authors were able to make the interior ofthenanotubes hydrophobic, whichallowedthenanotubemembranetopreferentiallyextractandtransportneutral hydrophobicmolecules. Whilesuchtechnologiesarestill tooexpensiveforcommercial-scalefoodappli-cations,asthetechnologyisfurtherdevelopedsuchmembranesmightbeusedinthe future for the isolationof food biomolecules withuniquefunctionalproperties.Another area of carbon-nanotube-based applications is the developmentof electrically conductive membranes. The high length per diameter ratio ofcarbonnanotubescanbeusedtoturnordinarysyntheticpolymers,whicharetypically electricalinsulators,intoconductingpolymers.InadditiontoFoodNanotechnology: CurrentDevelopmentsandFutureProspects 381theiruseintheelectronicandautomobileindustries,suchpolymerscouldalso be utilized to develop novel membranes that enhance the separation andenergyefciencyof valuable, delicatemolecules. Thebasic idea of thisdevelopment would be to incorporate minuscule carbon nanotubesuniformly into polymer substrates that could then be developed intomembranes. Membrane pervaporation of food avors, dehydration ofalcohols by pervaporation or membrane distillation, and temperature-swingabsorptionof volatileliquidfoods arejust someexamples of thepossibleapplications of such conducting membranes in food and associatedindustries (Moraru et al., 2003). Conducting polymers could also be used todevelop food-packaging films for new generations of quick and easy ready-to-eatmeals.Recentdevelopmentsindicatethatnanotubescanalsobeobtainedbycontrolledself-assemblyof biomolecules (i.e. proteins). Graveland-Bikker(2006) discoveredthat partiallyhydrolyzeda-lactalbuminorganizes intoa ten-start helix, forming tubes with diameters of 21 nm (Figure 21.6). Theyprobed themechanical strength of these nanotubesbyAFM, and observedthat theseartificial helical proteinself-assemblies yieldverystable, strongstructures. The authors suggested that such nanotubes can function either asa model systemfor artificial self-assembly, or as a nanostructure with potentialfor practical applications (Graveland-Bikker, 2006).IV.C. NanodeliverysystemsManyfunctional foodingredients, suchas vitamins, antimicrobials, anti-oxidants, avorings, colorants, or preservatives, areoftenincorporatedinFigure21.6 a-Lactalbuminnanotubes.Left: modelofa-lactalbuminnanotubewithouter diameter 21nm, inner diameter 8.7nm, pitch105nm, pitchangle58

, andinter-strand spacing of 5.4 nm; Right: microscopic image of nanotubes self-assembledafter partial proteolysisof a-lactalbuminat 50

Cfor 1.5h(Graveland-Bikker et al.,2006).382 CarmenMoraruetal.foods by means ofa carrier or delivery system (Weiss et al., 2006). In orderfor delivery systems to be effective, the encapsulated active compounds mustbe deliveredtothe appropriate sites, their concentrationmaintainedatsuitablelevels for longperiods of time, andtheir prematuredegradationprevented (Jelinski, 1999). By facilitating a precise control of properties andfunctionality at the molecular level, nanotechnology enables the de-velopmentofanumberofnovelsystemsthatcanbeusedtodeliverfunc-tional ingredients. Examples includenanometer-sizedassociationcolloidssuchas surfactant micelles, vesicles, bilayers, reversemicelles, andliquidcrystals. Themajor advantages of associationcolloids arethat theyformspontaneously, arethermodynamicallyfavorable, andaretypicallyatrans-parent solution; their major disadvantage is that they require a large quantityofsurfactant,whichcanleadtoproblemsrelatedtoflavor,cost,orlegality(Weissetal.,2006).IV.C.1. NanoemulsionsEmulsions withnanometer-sizedroplet diameters, producedusinghigh-pressurevalvehomogenizers or microuidizers, canbeusedas effectivenanodeliverysystems (Weiss et al., 2006). Encapsulatingfunctional com-ponents in the droplets of such nanoemulsions can enable the slowdown ofchemicaldegradationby engineeringthepropertiesoftheinterfaciallayersurroundingthem(McClementsandDecker,2000).Compounds with low water solubility have poor bioavailability. The useof nanoemulsions couldallowtheeffectivedeliveryof target compoundsthroughbiologicalbarriers.Recently,HuangandcollaboratorsatRutgersUniversity successfully prepared curcumin emulsions with controllable sizesranging from 200 nm to 5000 nm, with the purpose of creating an efcientdeliverysystemcapabletoimprovethebioavailabilityofcurcumin(Wanget al., 2008). TakhistovandPaul (2006) successfullyinvestigatedthefor-mationandstability ofnanoemulsionsforfoodfunctionalizationanddrugdeliveryusingtheeffect of electrochemical instabilityandsurfacetensiondrop at the polarized liquidliquid interface. When a potential difference ofhigher than the critical voltage of emulsification was applied to an oilwaterinterface, the interfacial tension was reduced to almost zero and spontaneousemulsification occurred (Takhistov and Paul, 2006). The authors were ableto control the structure and size of these emulsions, as shown in Figure 21.7.Sometimes it is desirable tocombine multiple bioactive compounds withina single formulation due to potential synergistic benets. A possible challengewould be the fact that different functional compounds are often incompatiblewitheachotherwithinaformulation. Theuseof multipleemulsions, forexample oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W)emulsions could represent a solution to this problem. Multiple emulsions canFoodNanotechnology: CurrentDevelopmentsandFutureProspects 383beusedtoencapsulatefunctional foodingredients withintheir individualphases, thus allowing the development of single delivery systems that containmultiple functional components. Multilayer emulsions, consisting of oildroplets (the core) surroundedby nanometer-thick layers (the shell) comprisedof differentpolyelectrolytes, representanotherexampleof anovel deliverysystem(Weiss et al., 2006). Theselayers areformedusingalayer-by-layerelectrostaticdepositionmethodthatinvolvessequentialadsorptionofpoly-electrolytes onto the surfaces of oppositely charged colloidal particles.Afunctional componenttrappedwithinthecoreof amultilayeremulsiondeliverysystemcouldbereleasedinresponsetoaspecificenvironmentaltrigger by designing the response of the shell to the environment (Weiss et al.,2006). One of the big advantages of this technology is that it could use foodingredients(proteins, polysaccharides, phospholipids)andestablishedfood-processing methods (homogenization, mixing), whichwouldincrease itschances of being easily adapted by the food industry.IV.C.2. BiopolymericnanoparticlesNanoparticles and nanospheres allowbetter encapsulation and releaseefciencyas comparedtotraditional encapsulationsystems; theyarepar-ticularlyattractivesincetheyaresmallenoughtoevenbeinjecteddirectlyintothecirculatorysystem(Bodmeieretal.,1989;Royetal.,1999).RoyFigure 21.7 ControlledO/Wemulsionstructures formedby Takhistov andPaul(2006): (a) irregular patterns, (b) chains of polarized droplets, (c) oil droplets network,and(d)internalorganizationofthedroplets network.384 CarmenMoraruetal.et al. (1999) showed that complex coacervates of DNAand chitosan,anatural polysaccharidefromcrustaceanshells, couldbeusedasdeliveryvehicles ingenetherapyandvaccinedesign. Their workresultedinim-munizationofmiceagainstthepeanutallergengene,whichindicatesthatoral immunization using DNA-functionalized nanoparticles could becomeaneffectivetreatmentforfoodallergies,aseriousproblemaffectingmanyconsumersaroundtheworld.Manynanostructuredparticlesaremadefrombiodegradablepolymers,such as polylactic acid (PLA). PLA is quickly removed from the bloodstreamandsequesteredintheliverandthekidneys,makingitidealforthetreat-ment of intracellular pathogens. One of the signicant limitations of PLA isthat it breaks down in intestinal uid, which limits its use as a carrier for oraldelivery (Weiss et al., 2006). These problems can be overcome by associatinga hydrophilic compound, such as polyethylene glycol (PEG). NanoparticlesmadefromPLA-PEGdiblockcopolymers formamicellar-likeassemblythatcanentrapacompoundtobedelivered(Rileyetal.,1999).Theefciencyof deliverysystemscanbeenhancedusingdendrimer-coated particles. They act as high-capacity loadable nanoreservoirs,sequesteringandsubsequentlyreleasingchargedmolecules fromsolutionduetothepresenceof anoppositelychargeddendrimer (KhopadeandCaruso,2002).Dendrimersaremonodispersemacromoleculeswithareg-ular, highly branched three-dimensional structure, and have a large numberof functionalities due to the high local density of active groups. Thischaracteristic makes them usable in a wide range of applications, such as forsensors,catalysts, oragentsforcontrolledreleaseandsite-specificdelivery(KhopadeandCaruso,2002).Averystableandprecisedeliverysystemisrepresentedbycochleates,whichare stable phospholipid-divalent cationprecipitates composed ofnaturally occurring materials. Cochleates have a multilayered structureconsisting of a large, continuous, solid, lipid bilayer sheet rolled up in a spiral(Figure21.8),anddelivertheircontentstotargetcellsthroughthefusionbetween the outer layer of the cochleate and the cell membrane (Santangeloet al., 2000;Gould-Fogeriteet al., 2003). Cochleatesresistenvironmentalattack; their solid-layered structure provides protection from degradation oftheencochleatedmolecules,evenwhenexposedtoharshenvironmentalconditions or enzymes, including protection from digestion in the stomach.Cochleates can be used for the encapsulation and delivery of many bioactivematerials, includingcompounds withpoor water solubility, proteinandpeptide drugs, and large hydrophilic molecules (Gould-Fogerite et al.,2003). It is possiblethat suchsystems will beusedinthefuturefor theencapsulation and targeted delivery and controlled release of functional foodmolecules.FoodNanotechnology: CurrentDevelopmentsandFutureProspects 385Nanoparticles canalsobeproducedusingfoodbiopolymers suchasproteins or polysaccharides, by promoting self-association or aggregation ofsinglebiopolymers,orbyinducingphaseseparationinmixedbiopolymersystems. Such nanoparticles can be used to encapsulate functionalingredients,whicharethenreleasedinresponsetospecicenvironmentaltriggers. A research group fromWageningen (The Netherlands) hasreportedthedevelopment of starch-basedmicro-andnano-particles thatbehavelikecolloidsinaqueoussolution(Dziechciareketal.,1998).Thesebiodegradable starch nanoparticles can be used in food applications such asmixing, emulsification, forimparting specific rheology to foods, or in non-food applications such as manufacturing of paints, inks, and coatings(Dziechciareketal.,1998).Salvona Technologies developed and patented a multicomponentdelivery system called MultiSal, which delivers multiple active immiscibleingredients suchas nutrients andavors andreleases themconsecutively(Shefer and Shefer, 2005). The systemconsists of solid hydrophobicnanospheres composedof a blendof food-grade hydrophobic materialsencapsulated in moisture-sensitive or pH-sensitive bioadhesive micro-spheres. Nanospheres witha diameter of about 0.010.5mm, generatedFigure21.8 Schematicrepresentationof physical states of AMBdeliverysuspen-sions, includingdisperseddetergentmicelles, orderedliposomal vesicles, androlledcrystallinecochleates(Santangeloetal., 2000).386 CarmenMoraruetal.using a proprietary suspension technology, are encapsulated in microspheresofabout2050 mmindiameter.When themicrosphereencounterswater,such as in saliva, it dissolves, releasing the nanospheres and other ingredients.IV.C.3. NanocompositesNanostructuring adds value to traditional materials by enhancing theirmechanical strength, conductivity, and ability to incorporate and efcientlydeliver activesubstances intobiological systems, at lowcost, andlimitedenvironmental impact. A promising class of new materials is represented bynanocomposites, whicharemadefromnanoscalestructures withuniquemorphology, andhave increasedmodulus andstrengthas well as goodbarrierproperties.The development of nanocomposites was inspired by biomineralization,the process in which an organic substance (protein, peptide, or lipid)interacts withaninorganicsubstance(i.e. calciumcarbonate) andformsmaterialswithincreasedtoughness. Oneexampleis apackagingmaterialmadeout of potatostarchandcalciumcarbonate; thematerial has goodthermal insulationpropertiesandislightweightandbiodegradable; italsohas been developed to replace the polystyrene clam-shell used for fast food(Stucky,1997).The report, Nanocomposites for Packaging: New Frontiers and FutureOpportunities, prepared by BRGTownsend and Packaging Strategies(U.S.), predictedthat by2011thetotal amount of nanocomposites willreach almost 100 million pounds, with about a half being used forcarbonated soft drinks packaging, followed by beer, and equally by meats, aswell as other foods and condiments (http://nanotechweb.org/). Nano-composites areregardedas thepotentiallyideal solutionfor plasticbeerbottles, since previous attempts to use plastic for this application haveresulted in spoilage and flavor problems. AJapanese company (NanoMaterial Inc.) developedamicrogravureprocess for coatingplasticfilmssuchas PET withananocompositebarrier material, whichprovedtobeabetter-performing, transparent, alternativetosilica-andalumina-coatedfood-packagingfilms, andhasgreatpotential forthemanufactureofbeerbottles(Moore,1999).Nanostructures can be also built from natural materials. Natural smectiteclays, particularly montmorillonite, a volcanic material that consists ofnanometer-thickplatelets, area popular sourcefor producingnanoclays(Quarmley and Rossi, 2001). Some U.S. companies (Nanocor Inc., Illinois;Southern Clay Products, Texas) are using montmorillonite as an additive innanocomposite production. Only a 35% montmorillonite addition makestheplasticlighter, stronger, andmoreheat-resistant, alongwithimprovedoxygen,carbondioxide,moisture,andvolatilebarrierproperties.MathewFoodNanotechnology: CurrentDevelopmentsandFutureProspects 387andDufresne(2002) preparedandexaminednanocomposites madefroma matrix of waxy maize starch plasticized with sorbitol and a stable aqueoussuspensionof tunicinwhiskersasthereinforcingphase. Parket al.(2003)developed thermoplastic starch/clay nanocomposites using a meltintercalationmethod. Witha5%byweightinclusionof theclays, highertensilepropertiesandalowerwatervaportransmissionratethanthether-moplasticstarchalonewereobtained.Chitosan,anontoxicnatural polysaccharidefoundinshellshthathasuniqueantifungalorantimicrobialproperties,hasa widerangeofapplica-tions, fromfood preservation, cosmetics, and wastewater treatment towound healing andproduction ofarticialskin (Risbud etal., 2000;JuangandShao,2002).Unfortunately,chitosanshydrophiliccharacterandpoormechanical properties in the presence of water and humidity limit itsapplication, althoughtheadditionof exfoliatedhydroxyapatitelayers wasobservedtosignificantly enhancethemechanicalandbarrierpropertiesofchitosanfilmsinhumidenvironments,whilemaintainingtheirantimicro-bialactivity(Weissetal.,2006).Thebarrier properties of nanocomposites, particularlythoseobtainedfromnatural materials, could be extremely useful for food-packagingapplications. The use of such materials could enhance considerably the shelflife of foods such as processed meats, cheese, confectionery, cereals, or boil-in-the-bagfoods.Intensescienticandtechnologiceffortsarebeingmadetodevelopnanocomposites, butduetotheexpectedcommercial impact,many oftheseeffortsaresurroundedbycondentiality.IV.C.4. NanolaminatesNanolaminates, consisting of two or more layers of material with nanometerdimensions, physically or chemically bonded to each other, could be used inthe future to make edible coatings or lms for food packaging or carriers forfunctional agents such as colors, avors, antioxidants, nutrients, andantimicrobials(Weisset al., 2006). Nanolaminates canbemadeusingthelayer-by-layer (LbL) depositiontechnique, inwhichchargedsurfaces arecoatedwithinterfacial films consistingof multiplenanolayersof differentmaterials. Thedepositioncouldbefacilitatedbyelectrostatic attraction,whichcauseschargedsubstancestobedepositedontooppositelychargedsurfaces. TheLbLtechnologyallows precisecontrol of thethickness andproperties of nanolaminates, and layers of 1100 nmthickness can beobtained (Weiss et al., 2006). According to Kotov (2003), nanolaminates aremore likely to be used as coatings instead of self-standing films because theyare veryfragile.Fooditemscouldbeencasedinnanolaminatesbydippingthemintoaseriesofsolutionscontainingsubstancesthatwouldadsorbtothe surface of the food, or by spraying these solutions onto the food surface388 CarmenMoraruetal.(Weissetal.,2006).Adsorbingsubstancesthatcouldbeusedtocreatethedifferentlayersincludenatural polyelectrolytes(proteins,polysaccharides),chargedlipids(phospholipids,surfactants),andcolloidalparticles(micelles,vesicles, droplets). This procedure could also be used to encapsulate variousactivefunctional componentssuchasantimicrobials,antibrowningagents,antioxidants,enzymes,flavors,orcolorsintothefilms,thusincreasingtheshelflifeandquality ofthecoatedfoods(Weissetal.,2006).IV.C.5. NanofibersNanobers are polymeric strands of sub-micrometer diameters andareproduced by interfacial polymerization and electrospinning. Electrospinningis usedtomakethinpolymer strands fromsolutionbyapplyingastrongelectric eld toa spinneret witha small capillaryorice. Polymer laments areformed from solution between two oppositely charged electrodes, with oneelectrode submerged in the polymer solution and the other one connected toacollector. Whentheelectrical forceattheinterfaceof apolymerliquidovercomes the surface tension, a charged jet is ejected (Fong and Reneker,2001). The jet initially extends in a straight line, then undergoes a vigorouswhipping motion caused by the electrohydrodynamic instability (Kim et al.,2006). This reduces theeffectivefiber diameter andaligns thepolymermolecules, thereby improving the mechanical properties of the fibers. As thesolvent evaporates, the polymer filament is collected ontoa grounded meshinthe form ofa non-woven mat(Figure21.9) with high surface areato massratio (101000 m2/g) (Kim et al., 2006).Electrospun polymer bers have unique mechanical, electrical, andthermal properties, and have applications in ltration, manufacture ofprotective clothing, and biomedical applications. The limited application ofFigure21.9 SEMimageofelectrospunfibersfrom9wt%DP210cellulose/NMMO/water solution with a rotating collector at 1.2 rpm and a flow rate of 0.03 mL/min (Kimetal., 2006).FoodNanotechnology: CurrentDevelopmentsandFutureProspects 389electrospunbers infood and agricultural systems is inpart due tothe fact thatthey are made primarily from synthetic polymers. Therefore, production ofnanobers from food biopolymers is likely to increase theiruse in the foodindustry. Potential food applications of nanobers include the reinforcementof food-packaging materials and the fabrication of nanostructured andmicrostructured scaffolding for bacterial cultures (Weiss et al., 2006).V. NANOTOOLSFORFOODANDBIO-SAFETYThe biosecurityof the food and water supply has become a serious concern inrecentyears,andnovelsolutionsarerequiredforthedevelopmentoffast,reliable, and highly sensitive biosensors for the detection of biological agentsinfoodor water. AresearchgroupfromNorthwesternUniversity hasdeveloped a method that produces nanoparticles with a triangular prismaticshape that canbe used indetecting biological threats suchas anthrax,smallpox, andtuberculosis, andawiderangeof geneticandpathogenicdiseases (Fellman, 2001). Chip-based sensing for rapid detection of biologicalpathogens is anothernew area with tremendous potential for application infood handling and processing, and in early warning systems for exposure toair- and water-borne bacteria, viruses, and other antigens. DNAmicroarrays,which consist of short strands of DNAsequences patterned on solid supports,are theprimarychoice forsuchsystems. Thetarget DNA extracted frompathogens canbe analyzedtoobtaindetailedsequence information, bysequence-specic binding (hybridization) to the microarrays.Fluorescencemicroscopy is usually used to detect the hybridization of uorescent-labeledtarget DNA in the microarrays. A novel method of making simple, linker-free, high-capacity DNA microarrays, based on highly porous organosilicatesupports, is currentlybeingdevelopedinHuangs laboratoryat RutgersUniversity.Ateam fromClemson University in South Carolina recently investigatedthe ability of synthetic adhesin-specic nanoparticles to irreversibly bind totargeted types of bacteria, inhibiting themfrombinding to and infecting theirhost (Latour et al., 2003). This research was aimed at reducing the infectioncapability of human foodborne enteropathogens (Campylobacter jejuni,Campylobacter coli, Salmonella enteritidis, and Escherichia coli) in poultry prod-ucts and used two types of nanoparticle systems. One type was based on theself-assemblyof organic polymers withcontrolled structures (i.e. poly-styrene), while the other systemwas based on inorganic nanoparticlesfunctionalized with polysaccharides and polypeptides that promote theadhesion of the targeted bacterial cells (Latour et al., 2003).Evena lowinfectious doseof E. coli O157:H7(less than100cells)requires the development of rapid and sensitive detection methods to390 CarmenMoraruetal.prevent widespread outbreaks. Traditional detection methods for traceamounts of bacteriarequireamplificationof thetarget organism. Recentprogress innanotechnology has led the way for development of noveldetectionmethods withhigher sensitivitytoeliminatethelaborious andtime-consumingamplificationprocess. Manyefforts havebeenmadeindevelopingnewprobematerialswithhighstabilityandquantumyield,toimprove the stability, sensitivity, and reproducibility of various bioassays forpathogenic cell detection. For example, semiconductor quantumdots(QDs) arepromisingmaterials that canbeusedtoimprovethebacterialdetection limit. Huangs group at Rutgers University has successfullydeveloped a simple bioconjugation procedure that allows the attachment ofwater-soluble cadmium tellurium QD to anti-E. coli antibodies (Kuo et al.,2008).Knownfortheiruniqueopticalprofiles,QDshavesize-dependenttunable photoluminescence with broad excitation spectra and narrowemission bandwidths. These characteristics allow simultaneous excitation ofparticles of different sizes at asinglewavelength. Inaddition, their highphotobleaching thresholdrenders possible the continuous or long-termmonitoring of slow biological processes. Today, QDs have becomepromisingprobematerials inthedevelopment of antibody-basedimmu-nosensors, demonstrating high stability, sensitivity, and reproducibility. Theresults of Huang and associates at Rutgers University suggest that the use ofQDsmakethedetectionofasinglepathogeniccellpossible.Many of the microbial safety problems encountered in the food industryare related to the contamination of food-processing equipment and surfaceswithbacteria, andbacterial andfungal spores. Microorganisms andtheirspores adhereto surfaces, especiallyto thosethatareporousorhavecracksand crevices. Spores are of particular concern, since they can surviveextremetemperaturesandadverseconditions.Oneofthemostimportantspore properties related to the contamination of surfaces is adhesion, whichhas beenidentiedas oneof theprincipal virulencefactors inmicroor-ganisms like Bacillus. Spore adhesion is a significant problem, particularly forpipelines inthedairyindustry, wherespores cangerminateandresultingbacteria can multiply and resporulate (Andersson et al., 1995; Bowen et al.,2000).Thequantificationofsporeadhesivenesshasbeenfacilitatedbythedevelopment of tools capable of analyzing single molecular mechanics.Bowen et al. (2000) used AFM to study the adhesive properties of Aspergillusniger, oneof themost commonmolds tocontaminatefoodandproducemycotoxins incereals andcereal products. CamesanoandLogan(2000)developedan AFM methodto probe theeffectsof pH, ionic strength,andbacterial surface polymers on the electrosteric repulsion between negativelycharged bacteria and AFM silicon nitride tips, finding that bacterial surfacepolymers were the dominating factor. Using a similar approach, Bowen et al.FoodNanotechnology: CurrentDevelopmentsandFutureProspects 391(2000) obtained adhesion properties and structural information aboutbacterial polysaccharides, which form biofouling layers on food-processingequipmentandothersurfaces. Theadhesionof lacticacidbacteriatotheintestinal epithelium, oneof themost important properties determiningprobiotic activity, has been studied using AFM by Zammaretti and Ubbink(2003). Understanding such interaction between contaminated surfaces andmicroorganisms allowed the design of materials that are resistant to bacterialadhesion (Husmark and Ronner, 1990; Razatos et al., 1998). Today,researchers are making efforts to develop a new generation of self-cleaningmaterials that are loaded with antimicrobial compounds, which can then bereleased under certain environmental conditions to kill contaminantmicrofloraonfoodsurfacesandequipment.Although such developments are much anticipated by the food industry,they are a rather long-term solution. Therefore, intervention strategies suchas disinfectionremainimportant weapons inghtingharmful microor-ganisms inthe foodindustry. The corrosive nature of disinfectants andbiocides commonlyused in food-processingenvironmentsmakes theiruseunsuitable for the decontamination of more sensitive equipment. In researchby Baker and associates (University of Michigan), nanoemulsions weredeveloped that are able to fuse with and subsequently disrupt the membraneof a varietyof different pathogens, suchas bacteria, spores, envelopedviruses, andfungal spores(Chepurnovet al., 2003). Sincenanoemulsionscan be produced cheaply and rapidly with high efficiency and stability, theyarelikelytobeusedextensivelyinthefoodindustry.VI. PROSPECTSANDCHALLENGESFORTHEFUTUREIn 2000, the National Science Foundation (NSF) estimated that in less than10 years, products made from nanotechnology will have a $1 trillion impactontheglobal economy, andthat thenanotechnologyindustryalonewillemploytwomillionworkers(Roccoetal.,2000).Currently,manyoftheworlds leading food companies such as Kraft, Unilever, Heinz, Nestle, andHershey are investing heavily in nanotechnology applications (Wolfe, 2005).In2006, participants at theFirst International FoodNanotechnologyConference(organizedbytheInstituteofFoodTechnologists)agreedthatnanotechnology is still in its infancy, with food applications more in a pre-infancystate;however,thereisagreatdealofenthusiasmandanticipationsurroundingthistechnology(Bugusuetal.,2006).At present, thefood industry is trying to identify opportunities andthemost promising discoveries in nanotechnology that can signicantlyenhancefoodprocessingandfoodproducts.Alimitednumber ofapplica-tions that deal withmatter at thenanoscaleandarerelevant tothefood392 CarmenMoraruetal.sector arecurrentlyavailable, andcanbecategorizedintwogroups: (1)functionalized membranes, which could be used to isolate and purify highlysensitive bioactive compounds and (2) nano-structuring technologies, suchas emulsication, dispersionandnano-aeration, or the encapsulationofactive compounds in food polymer matrices. The fabrication of foodbiopolymer-basednano-structuredmaterialswithuniquemechanical andfunctional properties; the synthesis of liposomes, which can be used for theencapsulation and targeted delivery of bioactive compounds through foods;or the development of nanosensors for pathogen detection, are all viewed asa starting point for the integration of nanotechnology into food science andfoodtechnology.Despite the slowonset of nanotechnology-based applications in the foodindustry,theparticipantsattheabove-mentionedmeetingagreedthatthefutureholds great promise, particularlyinthefollowingareas: (1) healthpromotionthroughfoods, by using foodmatrices as delivery tools forbioactive compounds, (2) development of ingredients with enhancedfunctionality, whichcouldbeusedtomanufacturefoods withnovel andunique avors andtextures, (3) development of novel, nano-structuredpackaging materials with enhanced barrier or self-sealing characteristics, (4)materialswithmicrobial-repellantcharacteristics, whichcouldbeusedtomanufacturefoodcontactsurfaces withself-sanitizingproperties,(5)novelprocessingtechnologies,and(6)advancedtools(i.e.nanosensors)forfoodsafetyshelflifeorqualitymonitoring(Bugusuetal.,2006).As with any new technology, a series of challenges can be expected. Oneof the big questions associated with the prospect of commercializing nanoapplications inthefoodsector is whetheror not this technologywill becost-effective in the near future, and if the benets will outweigh the costs inthe lowprot margin scenario of the food industry. It must also beconsidered that the implementation of some nanotechnology developmentscouldchange the wayin which the foodindustry operatesatthemoment,prompting the need forsignicant changes in current food regulations andlegislation.Presently,intheUnitedStates,therearenospecialregulationsfor theutilizationof nanotechnologyproducts infoods; intheEuropeanUnion(EU),althoughrecommendationsforspecialregulationshavebeenmade,lawshaveyettobechanged(Weissetal.,2006).Mediareportsregardingtherisksposedbysomenanoparticlesclearlydemonstrate that signicant research is still required to evaluate the toxicityof nanotechnologyproducts, particularlynanoparticles, andtoassess theenvironmental andpersonal safetyaspectsoftheiruse.Theriskscouldbepracticallyzero,orsignicant,dependingonthepropertiesof aparticularproductandexposurelevels(KuzmaandVerHage,2006).Fewriskassess-mentshavebeendonethatallow onetopredictwhathappenswhensuchFoodNanotechnology: CurrentDevelopmentsandFutureProspects 393extremely small particles, some designed to be biologically active, enter thehumanbody oraredispersedintheenvironment.TheFoodandDrugAdministration(FDA), thegovernment agencyresponsible forregulating food, dietary supplements, and drugs in the U.S.,states that it regulates products, not technologies, and that nanotechnologyproductswill beregulatedasCombinationProducts forwhichthereg-ulatory pathway has been established by statute (http://www.fda.gov/nanotechnology/regulation.html). The EuropeanCommissionhas takena more proactive approach and in February 2008 released a Code ofConduct for ResponsibleNanosciences andNanotechnologies Researchthatcontainsgeneral principlesandguidelinesforall memberstates. ThisCodeofConductinvitesallstakeholderstoactresponsibly andcooperatewith each other (.) in order to ensure that N&N research is undertaken inthe Community in a safe, ethical and effective framework, supportingsustainable economic, social and environmental development (http://cordis.europa.eu/nanotechnology/).It is very difcult to predict the long-term impact of any technology, andnanotechnologyisnoexception.While oneshouldnotunderestimateanypotential dangers caused by its misuse, it is almost generally recognized thatnanotechnologyhas thepotentialtomakesignicantcontributions fortheimprovement and even extension of life, partly through the improvement ofthe foodandagricultural system. 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