Innovative Food Processing Technologies 3 Volumes (2021, Elsevier)

2361 Pages·2021·158.814 MB·English

by  Kasiviswanathan Muthukumarappan, Kai Knoerzer

1.01 Overview of Research Needs, Future and Potential Applications of High-
Pressure Processing
RobertSevenich,Cornelia Rauh,andDietrich Knorr,Department ofFoodBiotechnology andFoodProcess Engineering,
TechnischeUniversität Berlin, Berlin, Germany
©2021ElsevierInc.Allrightsreserved.
1.01.1 Introduction 1
1.01.2 VegetativeMicroorganisms,Spores,Viruses,Parasites,BacteriophagesandNematodes 2
1.01.2.1 VegetativeMicroorganisms 2
1.01.2.2 Spores 3
1.01.2.3 Viruses,Bacteriophages,ParasitesandNematodes 4
1.01.3 ChemicalReactions:InfluenceonAllergens,Toxins(FoodBorneandAgriculturallyBased) 5
1.01.3.1 Allergens 5
1.01.3.2 Toxins 6
1.01.3.2.1 FoodProcessingContaminants 6
1.01.3.2.2 Aflatoxins,PesticidesandHerbicides 7
1.01.4 Process-Structure-Relationship 7
1.01.4.1 Starch 8
1.01.4.2 Pectin 8
1.01.4.3 Proteins 9
1.01.5 PackagingMaterial 10
1.01.5.1 Polylactides(PLA) 11
1.01.6 DataReportingandExperimentalDesign 11
1.01.7 Conclusion 11
References 14
1.01.1 Introduction
Today,theconsumers’demandforhighqualitysafefoodsrequiresthedevelopmentandapplicationofemergingprocessingtech-
nologiesforthegentlepasteurizationandsterilizationoffoods.Therefore,thefoodindustryislookingfornewwaystoproduce
safe,healthyandstablefoods.Onewaytomeetthisaimisapplyinghighpressure,intheorderof600MPa,tofoods,whichis
referredtointheliteratureascoldpasteurization(Matseretal.,2004;Knoerzeretal.,2010;Mújica-Pazetal.,2011).Currently,
high-pressureprocessing(HPP)inthefoodindustryissolelyusedforpasteurizationpurposes.Thetrendofusinghighpressure
as a technology for pasteurization of different kinds of foods, e.g., juices, ham, sauces and seafood is a growing sector in the
foodindustrysincethe1990’s(HoganandKelly,2005).Pasteurizationoffoodswithhighpressure(HP)iswellestablishedin
the food industry. In 2018, 500 industrial-scale high pressure systems were in use worldwide, producing approx. Four million
metrictonsannuallyofpressurizedfoods.Thereisstillaneedforresearchinthisfield,e.g.,consideringtheimpactonfoodstruc-
ture,foodquality,microorganisms,enzymeactivity,andnutrients.Furthermore,thereisahighacceptanceofpressurizedfoodson
theconsumersideduetothecleanlabelandhealthpromotingattributesthetechnologyoffers(Olsenetal.,2010),withoutwhich
industrialapplicationwouldbelessattractive.Despitethesteadilyincreasingcommercialproductionofhighpressuretreatedfood,
someimportantscientificandtechnologicalquestions,aswellassomepotentialotherapplicationsofHPParestillunresolved.One
oftheseissuesistheimpactofdifferentintrinsicandextrinsicfactorsontheinactivationmechanismsofvegetativebacteriaand
bacterialsporesunderpressure.Tounraveltheimpactofthedifferentpressureandtemperaturecombinationsonapossiblecell
deathorrecovery,detailedanalysesaboutthephysiologicalstateofthecellsandhowtheyareinfluencedbydifferentfoodcompo-
nentsareneeded.AccordingtoLeChatelier’sprinciple,inasystemfacingashiftofequilibrium,allcellularcomponentsareaffected
byhighpressure,includingthecellmembraneanditsmembraneproteins,enzymesandribosomesaswellastheentirecellmetab-
olism(WinterandJeworrek,2009;Georgetetal.,2015).Ingeneral,prokaryoticcellsshowahigherresistancetowardpressurethan
eukaryoticcells.Yeastsandmoldsareingeneralmorepressuresensitive,althoughascosporesofsomemoldssuchasByssochlamys
andTalaromycescanbeverypressureresistant(Smelt,1998;Considineetal.,2008;Georgetetal.,2015).Withinprokaryotes,gram
positivemicroorganismssuchasBacillus,Listeria,StaphylococcusandClostridiumhaveathickerpeptidoglycanlayerandaretherefore
morepressureresistantthangram-negativemicroorganisms(Smelt,1998;Considineetal.,2008;Dumayetal.,2010).Themech-
anismsleadingtocelldeathhavebeeninvestigatedinseveralbacterialspecies(Huangetal.,2014).However,theparticularevents
leadingtoinactivationarenotwellunderstood(Cheftel,1995;BuckowandHeinz,2008;Klotzetal.,2010).Highpressurebetween
300and800MPaatambienttemperaturescanleadtotheunfoldinganddenaturationofimportantcellenzymesandproteinsin
vegetativemicroorganisms(Rastogietal.,2007;Knorretal.,2011a,b),butthespecificpressureeffectsonmicroorganismsaremore
InnovativeFoodProcessingTechnologies,Volume1 https://doi.org/10.1016/B978-0-08-100596-5.22991-0 1
2 Overview ofResearch Needs,Future andPotential ApplicationsofHigh-Pressure Processing
complexandseveraldifferentmechanismsleadingtocelldeathcaninteractwhenhighpressuresareapplied.Primarily,pressureat
asufficientlyhighlevel,caninduceenzymeinactivation,membraneproteinsdenaturationandcellmembranerupturecausedby
aphasetransitionofthemembraneandchangeinitsfluidity(Anantaetal.,2005;Georgetetal.,2015).Thepressurelevelneededto
achievea5log reductionofpathogenicmicroorganismindifferentfood-productsrangesfrom300to800MPa(Hendrickxetal.,
10
2001)andoftensynergybetweenpressureandtemperatureisobserved(BuckowandHeinz,2008).Byincreasingtheprocesspres-
sure,itispossibletodecreasethetemperatureneededtoachievethesameinactivation.Accordingtotheliterature,thepressure
inducedeffectsleadingtocelldeathofvegetativemicroorganismscanbeattributedtofourfactors:
(i) Proteinandenzymeunfolding,includingpartialorcompletedenaturation
(ii) Cellmembranesundergoingaphasetransitionandchangeoffluidity
(iii) Disintegrationofribosomesintheirsubunits
(iv) Intracellular pH changes related to the inactivation of enzymes and membrane damage (Knorr et al., 2011a,b; Molina-
Höppneretal.,2013;Georgetetal.,2015)
Further,theinfluenceonthefoodmatrixstillneedsclarificationintermsofwhatcompoundsareformedordestroyedincompar-
isontotheconventionalprocess.Also,aclearassessmentofwhatthepotentialandlimitsofHPPare,isstillmissingtothispoint.
Somewell-knownpotentialandlimitsare:
(i) AdvantagesandPotentials
Rapid, quasi-instantaneous uniform distribution throughout the sample; Minimal or reduced thermal exposure; Instant
temperature increase and subsequent cooling upon depressurization; Suitable forhigh moisture–content foods; in package
processing; Suitable for both liquid and pumpable foods; Independent of product shape and size; Opportunity for novel
productformulation;Distinctproductsthroughpressureeffectssuchasproteindenaturation,carbohydrategelatinization,and
fatcrystallization;Withinsomepressure-thermalboundaryconditions,pressureacceleratesmicrobialinactivation;Consumer
acceptanceasaphysicalprocess.
(ii) Limits
Batch or semi-continuous operation; Preheating step for pressure-assisted thermal processing (PATP) required; Thermal
nonuniformity during PATP; Not suitable for products containing dissimilar compressibility materials such as foams;
Throughputlimitedduetobatchoperation;Variableefficacyinenzymeinactivation;pressurealonecannotinactivatebacterial
spores;Higherprocessingcosts.
SomeauthorshavelookedbeyondtheobviousapplicationofHPP,otherthanjustmimickingofthermalprocessing.Anoverview
ofsomeoftheapplicationscanbefoundintheliterature(Smelt,1998;Oeyetal.,2008;Verbeystetal.,2010;VanDerPlancken
etal.,2012).Mostoftheseauthorsarereferringtothepromisinguseofhigh-pressureprocessingasagentlepreservationtechnique
butarealsomentioningthepossibleapplications,ifthefoodsafetyisgiven,toaltertexture,increasethebioavailabilityofcertain
healthpromotingcompounds,allergenicityreductionaswellasvitaminretention.
Initially,theempiricapproachoftrialanerrorwasused,whichdrovetheevolutionofhighpressureprocessingfrominactivation
studiesofvegetativemicroorganism(Hite,1899;TimsonandShort,1965;Saleetal.,1970;Metricketal.,1989;Cheftel,1995;Fior-
ettoetal.,2005;Georgetetal.,2015)toinactivationofenzymes(Silaetal.,2008;Rauhetal.,2009;Knorretal.,2011b;Grauwet
etal.,2012)toshuckingofcrustaceans(Kingsley2014)tosporeinactivation(Saleetal.,1970;Reddyetal.,2003;Blacketal.,2007;
Olivieretal.,2012;SetlowandMarkland,2012;Reinekeetal.,2013a,b;Olivieretal.,2015;SevenichandMathys,2018)tostruc-
ture/textureinducedbyhighpressure(Oeyetal.,2008;Silaetal.,2008;SikesandWarner,2016;Balasubramaniametal.,2016;Thai
UnionGroup,2017;Simetal.,2019)tocurrentlythelatestfrontieroftheinfluenceonchemicalreactionspathways(e.g.,degra-
dationofvitamins,oxidationofpolyunsaturatedfattyacidsandmitigationoffoodprocesscontaminants)(Oeyetal.,2008;Ver-
beystetal.,2010;VanDerPlanckenetal.,2012;Sevenichetal.,2013).Toseebeyondtheobvious,onemustaskwhatisdifferent
comparedtothethermalprocessesandwhy.Howcanthisdifferencebeusedasapotentialandadvantagetocreateforexamplenew
functionalfoodingredients,foodpropertiesandhealthfoods?Someoftheseaspectsaretackledandcoveredbysomerecentreviews
(Balasubramaniametal.,2016;Huangetal.,2017).
Anotherissuethatneedsfurtherresearchfocuscouldbetothinkofnovelcombinationprocessesasforexampledoneinthepast
withHPP/PEF,highpressurethermalsterilization,pressureassistedthermalsterilization(PATS),pressureinducedfreezing(PIF),
pressureassistedfreezing(PAF),highpressurehomogenization(HPH)andhighpressureextraction(Volkertetal.,2008;Parketal.,
2013;Huangetal.,2013;Sevenichetal.,2015a,b;SevenichandMathys,2018).
Thisarticlewillreviewtherecentliteratureandwilldiveintodifferentareaswheretheauthorsconsiderhighpressureprocessing
tohaveasignificantimpactinthecomingyears.
1.01.2 Vegetative Microorganisms, Spores, Viruses, Parasites, Bacteriophages and Nematodes
1.01.2.1 Vegetative Microorganisms
TheuseofHPPtoinactivatepathogenicvegetativemicroorganismshasbeenlargelyinvestigatedforthepasteurizationofcommer-
cialproductsfordecades(BuckowandHeinz,2008).In1899,Hite(1899)wasfirsttoconductexperimentsusinghighpressurein
combinationswithfoodstoextendshelflife,andreportedthatmilkstayedsweetlongerafterthetreatmentwithhighpressure.Since
OverviewofResearch Needs,Future andPotential ApplicationsofHigh-Pressure Processing 3
then,significantresearcheffortshavefocusedonunderstandingtheunderlyingmechanismsoftheinactivationofmicroorganisms
underhighpressureconditions.HPPoffersalowerthermalinputintotheproductbycomparisonwithconventionalthermaltreat-
mentandthereforeincreasesthequalityofthefoodwhilemaintainingfoodsafety(Smelt,1998;HoganandKelly,2005;Balasu-
bramaniam et al., 2008; Bermudez-Aguirre and Barbosa-Canovas, 2011; Barba et al., 2012). Despite the steadily increasing
commercial production of high pressure pasteurized food with several millions of tons per year (Aganovic et al., 2017), some
importantscientificandtechnologicalquestionsarestillunsolved.
Oneoftheseissuesistheimpactofdifferentintrinsicandextrinsicfactorsontheinactivationmechanismsofvegetativebacteria
andbacterialsporesunderpressure.Tounraveltheimpactofthedifferentpressureandtemperaturecombinationsonapossiblecell
deathorrecovery,detailedanalysesaboutthephysiologicalstateofthecellsandhowtheyareinfluencedbydifferentfoodcompo-
nents are needed, In recent years, a common world-wide concern has been foodborne outbreaks with pathogens like EHEC
(O157:H5;O104:H4)andothers(AdleyandRyan,2016).Thecontaminationofthefood supplywith spoilageandpathogenic
microorganismscontinuestobeaglobalproblem,despitethewiderangeofpreservationmethodsemployed(Kaczmareketal.,
2019).Despitesignificantadvancesinfoodprocessingtechnologies(hurdleconcept,newinnovativenon-thermaltechnologies),
anannualestimated76millioncasesoffoodborneillnessesoccurintheUSalone,resultinginapproximately5000deaths(Scallan
etal.,2011).ThereportbytheUSCenterfordiseasecontrolandpreventioncenterstatesthatmost(58%)illnesseswerecausedby
norovirus,followedbynontyphoidalSalmonellaspp.(11%),Clostridiumperfringens(10%),andCampylobacterspp.(9%).Leading
causesofhospitalizationwerenontyphoidalS.spp.(35%),norovirus(26%),C.spp.(15%),andToxoplasmagondii(8%).Leading
causesofdeathwerenontyphoidalS.spp.(28%),T.gondii(24%),Listeriamonocytogenes(19%),andnorovirus(11%).Intheyear
2000,e.g.,approximately2.4millionpoundsofbeefwererecalledduetopossiblecontaminationwithEscherichiacoliO157:H7
(Kaczmarek et al., 2019). Newest studies from the WHO (2015) on foodborne diseases caused by pathogenic microorganisms,
suchasSalmonella,Campylobacter,EHECandNorovirus,showthatworldwide1in10peoplefallilleveryyearfromeatingcontam-
inatedfoodand420,000dieasaresult.Here,theapplicationofhighpressureincombinationwithmildtemperaturesatpressures
between300and700MPacouldpossiblybeusedtoinactivatevegetativepathogenicmicroorganismsaswellasseveralenzymes,
whichcausefooddeterioration.TheresistancetowardtemperatureofthepathogenicEscherichiacolistrainsisusuallyhigherthan
itsnon-pathogeniccounterpart(Garcia-Graellsetal.,1998).Hence,amoreintenseheattreatmentneedstobeapplied.Themore
complexandresistantthemicroorganismthemoreintensemustbethetreatment.IncomparisontothepathogenicE.coli,higher
temperaturesandhigherpressuresmustbeappliedtoinactivatespores(Reinekeetal.,2013a,b).Thisbecomesevenmorecomplex
if this is conducted in a real food system since here baro-protective effects can occur and the severe heat treatment can lead to
unwantedchangesinthefoodmatrix,leadingtotheformationofunwantedandpossiblyunhealthycompoundsinthefoodstuff.
Thecomparisonofpressureresistanceamongvegetativefood-bornepathogensrevealedthatstrainsofEscherichiacoliO157:H7were
themostresistantsofarencountered.TheUSDA(2012)hasrequirementsofE.coliO157:H7astheindicatorstrainforreprocessing,
anHPPprocessthatachievesa5-log E.coliO157:H7reductionshouldbesufficientenoughtoproducemicrobiallysafeproducts.
10
OtherpossibleindicatorstomonitorifHPPissufficientlyappliedduringprocessingisbycoppertabletsincombinationwith
Heckelvalue(rateofdensitychangeofe.g.,chopperunderpressure).Theincreaseindensityovertheentirepressurerangeislinear.
Thetabletscanbeplacedinsidethevesselaswellasdirectlyintothefood.Measurementsat400MParevealedthatfortrialswith
hamtheproductexperienced9MPalessthanthesurroundingwater.Thiscouldleadtoshortcomingsintermsofsufficientinac-
tivation.Thetrialwasnotrepeatedat600MPa(MinerichandLabuza,2003).
Anotherphenomenonthatcouldleadtofalseresultsintermsofinactivationkineticisagglomeration,whichisverycommonfor
vegetativemicroorganisms aswellasspores.Theeffectivenessofinactivation processesisoftenverifiedbychallengetestsusing
foodsthathavebeenspikedwithhighlyconcentratedmicrobesuspensions. Due topreparation, storageandhandling ofthose
suspensions,theclumpingandtheformationofaggregatescanhardlybeavoided.Thisphenomenoniswellknown,firstreported
ontheeffectofsporeagglomerationsoninactivation.However,theimportanceforthequantitativeassessmentofsurvivorsininac-
tivationexperimentshasrarelybeenaddressed.Itsimportancebecomesevidentbythefollowing:Agglomeratesproduceonecolony
forahighnumberofcellsupto103CFU’s.Consequently,agglomeratesofunknowncellnumbersarealwayscountedasonespore
untilallsporesintheagglomerateareinactivated.Beyondthis,agglomerationanddisintegrationcanchangethecolonyforming
unitspermilliliter.Inthiscontextamodelforthediscussedphenomenonwasdeveloped(MathysandHeinz,2006).
1.01.2.2 Spores
Theinactivationofbacterialendosporesbypressureisgenerallyconsideredtorelyonpressure-inducedsporegermination,followed
by inactivation of germinated spores (Setlow, 2003; Margosch et al., 2004; Margosch et al., 2004). In the past decades, other
possiblenon-physiologicalpathwaysofsporegerminationhavebeendetected.Non-nutrientgerminationcanbefurthercatego-
rized into a (recently discovered) second physiological and several non-physiological routes. The physiological routes include
germinationinitiatedbyeukaryotic-likeserine/threoninekinase,whichislocatedintheinnersporemembranelikenutrientrecep-
tors.Thiskinase,whichispresentinBacillusandClostridiumspecies,recognizespeptidoglycanfragments.Non-physiologicalgermi-
nationpathwaysinitiatesporegerminationbybypassingindividualgerminationsteps.Thiscouldbestimulatedbyphysiochemical
agents,suchasexogenousCa-DPA(Paidhungatetal.,2002;Moir,2006),whichdirectlyactivatestheCLECwlJ,orcationicsurfac-
tantssuchasdodecylamine(Setlow,2003),whichinterfereswiththeinnersporemembraneandcausesadirectreleaseofCa-DPA.
Atpressuresbetween100and400MPaithasbeenshownthatthenGeRofBacillussubtilisandBacilluscereusaretriggered.Thespores
germinatedquitewellbetweenpressuresof100–200MPaandledtoamaximum4log inactivationbutthepressureinduced
10
4 Overview ofResearch Needs,Future andPotential ApplicationsofHigh-Pressure Processing
physiologicalgerminationdecreasedforhigherpressures,indicatingthatotherpathwaysmustbeactive(Wuytacketal.,1998;Paid-
hungatetal.,2002;Reinekeetal.,2013a,b).Atreatmentof200–400MPaat40(cid:1)Cfor30minshowedgerminationofthesporesbut
negligibleinactivation(Wuytacketal.,1998).
Toachieveaquickandsuddeninactivationofspores,whichisrelevantforfoodprocessing,pressuresabove500MPamustbe
appliedincombinationwithtemperaturesabove60(cid:1)C.Undertheseconditions,Paidhungatetal.(2002)wereabletogerminate
B.subtilissporesthatlackallmajornutrientreceptors.Thissuggestsadirectopeningofthespores’Ca–DPAchannels,agermination
mechanismidentifiedasactiveat200MPaandmoderatetemperatures(<50(cid:1)C)usingB.subtilismutantstrainsthatlackthenGeR.
ThesefindingswerealsoverifiedbyReinekeetal.(2012)forpressures(cid:3)600MPaandtemperatures(cid:3)60(cid:1)C.Thefollowingstep,
whichisrapidreleaseofCa–DPAunderpressure,isaccompaniedbycorehydration.Thisstepofgerminationisthecrucialstepwith
regardtolossofresistance,anditisthereforeofgreatinterestforavarietyofsterilizationtechniquesandresearch(Reinekeetal.,
2013a,b).Therefore,theabilityofthesporetoretaintheDPAaslongaspossibleundertheseconditionsbecomestheratelimiting
stepofthesporeinactivation(Margoschetal.,2006;Reinekeetal.,2013a,b).ThissuggeststhatthestructuremostsusceptibletoHP
(600MPa) and high temperatures (60(cid:1)C) is the inner spore membrane or its associated membrane proteins (Reineke et al.,
2013a,b). At pressures above or equal to 400MPa, when an opening of the Ca - Dipicolinic acid (DPA) - channels occur, the
followinghappens:(i)DPAisreleasedfromthesporecore;(ii)thesporecoregetshydrated;and(iii)thesporebecomesthermo-
andpressuresensitiveandcanbeinactivated(Reinekeetal.,2012).Further,athresholdpressureof600MPawasestablished;atand
abovethispressureleveltheDPA-releaseisdominatedbytemperature.Toguaranteeasuccessfulinactivationofsporesbypressures
of600MPa,manyresearchersrecommendatreatmentat90–121(cid:1)C(Margoschetal.,2004;JulianoandBarbosa-Canovas,2005;
Margoschetal.,2006;Mathysetal.,2007;Knorretal.,2011b;Georgetetal.,2015;Sevenichetal.,2016)duetothesynergisticeffect
pressureandtemperaturehaveonthesporeinactivation(Olivieretal.,2015).Incomparisontoconventionalretorting,thiscould
reducethethermalloadappliedtotheproductwithoutaffectingthesafetyorthequalityofthefood.Twosterilizationapproaches
canbederivedfromthis,bothofwhichneedtheadiabaticheatofcompressiontoreachthetargettemperature:
(cid:129)
Pressureassistedthermalsterilization(PATS):pressureisneglectedandonlyseenasthemethodtoreachtheendtemperature
faster(Dunneetal.,2010)
(cid:129)
HighPressureThermalSterilization(HPTS)whichtakesintoaccounttheimpactofpressureonthesporeinactivation(Mathys,
2008;Knorretal.,2011)
Recently,thedifferencesingerminationunderpressurebetweenClostridiumsporesandBacilluswererevealed,showinginteresting
insights(Paredes-Sabja et al., 2011; Lenz and Vogel, 2015; Doona et al., 2016). InBacillus spp.,DPArelease triggers cortex lytic
enzyme (CLE) activation; CLE action is not essential for DPA release, but it can accelerate it. In Clostridium difficile or
C.perfringens,theinitiationofcortexhydrolysisbySleCprecedesandtriggersDPArelease.UsingC.difficilespores,whichlackinner
sporegerminantreceptors,550MPatreatmenttriggeredDPArelease.However,sporegerminationwasnotcompletedbecausecortex
hydrolysis is notactivated by DPA release. C. perfringens spores became activated by high pressures during thecome-up time to
550MPa.Itcouldbeshownthat(i)theactionof550MPadirectlystimulatedDPAreleaseand(ii)activationofinnermembrane
germinantreceptorsduringthecome-uptimeto550MPaandthatthisactivatedstateofgerminantreceptorsismaintainedforawhile
andactivatescortexlyticenzymes(Doonaetal.,2016).Thisisonlyvalidiftemperaturesbelow80(cid:1)Careused;ifaheatshockT
>80(cid:1)Cisapplied,sporegerminationcanbecompleted.Thesefindingswereveryinterestingsincetheyshowedhowdifferentspores
areandhowimportantprocessknowledgeandmicrobiologicalknowledgearetocreatesafeprocesses,suchastheHPTS.
Thequestionofwhatkindofindicatorstrainshouldbeusedistothispointstillnotsettled.Someresearchersusethenon-
pathogenicBacillusamyloliquefaciens,insteadofClostridiumbotulinum,asasurrogatetocheckforsufficientinactivationrespectively
sterilizationsuccess(Olivieretal.,2015;Margoschetal.,2006;Sevenichetal.,2016).Sinceotherstrainsusuallyusedtotestfor
sterilizationlikeGeobacillusstearothermophilusandClostridiumsporogenesareveryhighpressurehightemperaturesensitive(Sevenich
etal.,2016).Itisalsoimportanttonotethatonecannotconcludebasedoninactivationkineticsobtainedinbufferormodelfood
systemshowtheinactivationofsporeswillbeinrealfoodsystems(Georgetetal.,2015;Sevenichetal.,2015a,b;Sevenichand
Mathys,2018).TheUSFDArecommendstestingfora4log inactivationofClostridiumbotulinum(Dunne,2009;Balasubrama-
10
niamandLelieveld,2016).
1.01.2.3 Viruses, Bacteriophages, Parasites andNematodes
Intotal,thereare31knownpathogensthatcausefoodbornediseases,21arebacteriarelated(E.coli,Salmonella,Listeriaetc.),five
virusesandfiveparasites(AdleyandRyan,2016).Especiallyvirusesandparasitesaregenerallyunderrecognizedifitcomestofood
bornediseases.Thegrowingglobalinterconnectionofthefoodsupplychainandmoresophisticatedanalyticaltoolsarereasonsfor
theincreaseddiagnosisoffoodbornediseases(Dornyetal.,2009).Foodbornediseasesalsohaveanimpactontheeconomy,each
incidentwascalculatedwith(cid:4)1500$/personandatotalannuallyestimatedcostof$75billion,intheUnitedStatesin2015alone
(Moyeetal.,2018).Beforegoingintofurtherdetailonhowhigh-pressureprocessingmighthaveanimpactontheinactivationof
theseorganisms,ashortintroductiononwhatdefinesthesegroups,wheretheycancomeincontactwithfoodsandwhatdisease
theycancause,isgiven.
(i) Viruses/Bacteriophages:Avirusisasmallinfectiousvehiclethatcannotgroworreproducewithoutalivingcell.Avirusinvades
livingcellsandusestheirchemicalmachinerytokeepitselfaliveandtoreplicateitself.Itmayreproducewithfidelityorwith
OverviewofResearch Needs,Future andPotential ApplicationsofHigh-Pressure Processing 5
errors(mutations);thisabilitytomutateisresponsiblefortheabilityofsomevirusestochangeslightlyineachinfectedperson,
makingtreatmentdifficult.Incommonusage,thetermvirusisusedtodescribevirusesthatcanonlyaffecthumans.Viruses
causemanycommonhumaninfectionsandarealsoresponsibleforseveralrarediseases.Thetwomainfoodbornevirusesof
concerninthefoodindustryaretheNorovirusandHepatitisAvirus.In2011,theNoroviruswasthemaincauseoffoodborne
illnessesintheUnitedStates(AdleyandRyan,2016;Panetal.,2016).
Therearemainlytwofoodtypesthathaveahighriskforcontaminationduringproductionorharvest.Onewouldbefruitsand
vegetables,wherethecontaminationcanbeduetotheuseofnon-potablewaterforcleaningorfecallycontaminatedfingers
(Kingsley,2013).Thesecondfoodtypehavingelevatedriskofcontaininghighamountsofvirusesareshellfish(oysters,clams,
cocklesetc.).Duetotheirnatureasfilterfeedersandthehighamountsofvirusesfoundinseawater(9(cid:5)108virons/mL),they
can accumulate viruses as much as 1000-fold (Kingsley 2013, 2014). Bacteriophages are viruses that can only attack and
replicateinbacteriaandarchaea.Phageshavebeenusedsincethelate19thcenturyasanalternativetoantibioticsintheformer
SovietUnionandCentralEurope,aswellasinFrance.Theyareseenasapossibletherapyagainstmulti-drug-resistantstrainsof
many bacteria (phage therapy). Since 2006, the United States Food and Drug Administration (FDA) and United States
Department of Agriculture (USDA) have approved several bacteriophage products. LMP-102 (Intralytix) was approved for
treatingready-to-eat(RTE)poultryandmeatproducts.Inthatsameyear,theFDAapprovedLISTEX(developedandproduced
byMicreos)usingbacteriophagesoncheesetokillListeriamonocytogenesbacteria,inordertogivethemgenerallyrecognizedas
safe(GRAS)status.InJuly2007,thesamebacteriophagewasapprovedforuseonallfoodproducts.In2011,USDAconfirmed
thatLISTEXisacleanlabelprocessingaid.Researchinthefieldoffoodsafetyiscontinuingtoseeiflyticphagesareaviable
optiontocontrolotherfood-bornepathogensinvariousfoodproducts(Moyeetal.,2018).
(ii) Parasites including nematodes: Parasitism is a relationship (consumer-resource interaction) between species, where one
organismlivesonorinanotherorganismontheexpenseofthehost.Parasitesincludeprotozoans,tapeworms,nematodesetc.
Someofthemajorparasitesthatareofconcernforthefoodindustryaree.g.,Echinococcusmultilocularisassociatedwithberries
andwater;Cryptosporidiumspp.arebeginningtobeassociatednotonlywithwater,butalsowithsalads;Trypanosomacruziis
foundinjuices;Trichinellaspp.arenowadaysfoundingameanimals;Anisakiasisisbecomingaglobalproblemastheworld
developsatasteforsushi(Robertson,2018).
Literatureonthepressureinactivationofvirusesisscarceandthereareonlyahandfulofpapersthataredealingwithinactivation
studiesofvirusesinfoods(Kovaetal.,2010;Kingsley2013,2014;Balasubramaniametal.,2015).Especiallyresearchdealingwith
theinactivationmechanismarelimited(Panetal.,2016).Researchwithhumannorovirusstrainsandvirusesingeneralisdifficult
duetothelackofsuitablelaboratory animalsandtheinabilitytopropagatethevirusinvitro.AstudyconductedbyWiezorek
(2012)withPixunavirus,whichisasurrogateformanyhumanparthenogenicalphavirus,showedthatPixunacouldbeinactivated
by109withatreatmentat150MPa/37(cid:1)C.
Theinactivationofvirusesviahighpressureprocessingisassociatedwithalteringtheproteinslocatedatthecapsidofthevirus.
DuetoconformationchangeoftheseproteinsthevirusisnotabletodockontothehostcellandreleasetheRNAintothecell
(Moronietal.,2002;Kovaetal.,2010;Kingsley,2013;Louetal.,2015).Non-envelopedvirusesaregenerallymoresensitivetoward
highpressureprocessingincomparisontoenvelopedviruses,whichhavealipidenvelope.Theinactivationofvirusesisdepending,
asvalidforsporesandbacteria,onthetemperature,pressureandtimeapplied(Panetal.,2016).Pressuresabove400MPaareeffi-
cientenoughtoinactivatemostviruses(Kovaetal.,2010).Although,higherpressuresdonotnecessarilyneedtoleadtoamore
efficientinactivationofamoreresistantvirus.
Thestudiesfoundintheliteraturesuggestthatviruseslikehumannorovirus(Norwalk8fIIb)inoculatedinoysters(104)canbe
completelyinactivatedby600MPaand5min(Leonetal.,2011).StudieswithHepatitisAvirusalsoinoculatedinoysterswith106
showedaninactivationofmorethan3log after400MPaand1min(Kingsley,2013).Rotavirusinbuffersolutionwasinactivated
10
by8log at300MPaand2min(KhadreandYousef,2002).VerypressureresistantarethevirusesAichivirusandPoliovirus,which
10
werecompletelyresistantat600MPaand5min(Kingsleyetal.,2002).
Forviruses,theUSFDAisproposingamaximumdesiredreductioninviruslevelof5log (Panetal.,2016).
10
Theliteratureonnematodesandotherparasitesisveryscarceandvirtuallynon-existing.Thereisonepublicationontheinac-
tivationofapinewoodnematodeinwoodchips,inoculatedwith1.2(cid:5)105byhighpressureprocessing.Hereitwasshownthatthe
nematodeswerecompletelyinactivatedby30MPaataholdingtimeof5min(Fonsecaetal.,2014).Thissuggeststhatthebiggerthe
organismtheeasieritcanbeinactivatedbyhighpressureprocessing.Thequestionthatstillneedstobeansweredisifthatisalso
validforotherparasiteslikeCryptosporidium,Trypanosomaetc.
Theresearchontheinfluenceofhighpressureprocessingonvirusesandparasitesneedstobedrivenforwardsinceitisaprom-
isingalternativetoguaranteethesafetyofusuallynon-processedorgentleprocessedfreshproducts.
1.01.3 Chemical Reactions: Influence on Allergens, Toxins (Food Borne and Agriculturally Based)
1.01.3.1 Allergens
Allergyisafalse,hypersensitiveandintenseimmuneresponsetowardtypicallyharmlesssubstancesintheenvironment.Foodcan
beatriggerfortheimmunesystemtooverreact,especiallydairy,egg,soy,peach,cherry,selfish,wheat,nutsandapplecancausean
allergicreaction(SomkutiandSmeller,2013).Foodallergyismoreprevalentinyoungchildren(5%)but3%–4%ofadultsalso
exhibitaformoffoodallergy.
6 Overview ofResearch Needs,Future andPotential ApplicationsofHigh-Pressure Processing
ThebeginningofatypeIallergicreactionisthesensitizationtoanallergen.Theinitialcontactofanallergenwiththemucosaof
asusceptiveorganismisfollowedbyacomplexseriesofevents,leadingtotheproductionofallergenspecificimmunoglobulinE
(IgE).Theeffectorphaseofanallergicreactionisinitiateduponsecondexposuretotheallergen.AllergenbindingtothespecificIgE
antibodyonthemastcellswillcauseaninflammatoryresponseduetothereleaseofhistamineandothermediators.Notallaller-
gensareabletosensitize,i.e.,inducetheproductionofspecificIgE-typeantibodies(SomkutiandSmeller,2013;Ontiverosetal.,
2015;Ekezieetal.,2018).Allergenswhicharecapabletobothsensitizeandtriggerallergicreactionsarecalledcompleteallergens.
CrossreactiveallergensbindtoIgEantibodiesthatarepresentinthebodyduetoanearliersensitizationbyanotherallergen.There
aremorethan6000allergenswhichcanhaveanegativeimpactandtherearecurrentlynoacceptedtherapeuticapproachesother
thanavoidingthefoodsthatcontainthepossibleallergen(Ontiverosetal.,2015;Meinlschmidtetal.,2016).Here,thetargeted
treatmentbyfoodprocessingtechnologies,suchashighpressure,enzymatichydrolyzes,heattreatmentorcombinedprocesses,
couldbeapromisingstrategytocreatehypoallergenicfoods.Togainknowledgeifafoodproteinisallergenicornotitneedsto
becharacterizedbytheallergic(epitopes)andnon-allergiccomponents;thiscanbedonewiththehelpofimmune-informatics
(Ontiverosetal.,2015).Themainsequence/patterninallergenicproteins’secondarystructureare(1)antiparallelb-strands;(2)
antiparallelb-sheets;(3)aþbstructuresand(4)a-helicalproteins(SomkutiandSmeller,2013).Sincehighpressureprocessing
can have an impact on the functionality of proteins by altering the secondary, tertiary and quaternary structure of the protein
duetochangesinelectrostaticandhydrophobicinteractionsitsurelyinfluencesthereactivepropertiesofallergenicproteins(Jimé-
nez-Saizetal.,2015).Theapplication,alsoincombinationwithotherprocesses,isaninterestingtooltocreatefoodswithreduced
foodallergenicity.SomkuttiandSmeller(2013)mentionedintheirreviewthatthreequestionsneedtobediscussedtofindoutif
highpressureissuitable:(1)Howhighisthepressureneededtounfoldtheprotein?(2)Istheunfoldingreversible?and(3)Howis
thebindingofIgEtotheallergen?
Ingeneral,itcanbesaidthatforsomeofthemajorfoodallergenslikeMalD1(apple),Bosd5(Milk),Gald2(Egg),Arah2
(Peanut),Gadm1(fish),pressuresandtemperaturesof150–600MPaand30–80(cid:1)Careneeded(SomkutiandSmeller,2013).The
mechanismofapotentialallergenicreductionwhileapplyinghighpressureprocessingiseitherthemaskingofepitopesdueto
conformationalchangesinducedbyhighpressure,orthehigherexposureofepitopesbutthereforeleadingtohigherenzymatic
hydrolyzes(Peñasetal.,2008;Meinlschmidtetal.,2016).Thesecondmechanismwillonlyworkifthefood/allergensaretreated
withenzymeslikepepsin,chymotrypsinorpapainafterthetreatment,otherwiseitwouldmakethefoodevenmoreallergenic.It
could be shown that the allergenic potential of the walnut allergens Jug r 1–5 can be reduced by pressures ranging from 550–
650MPa(Ekezieetal.,2018).Furtheradecreaseof40%–60%ofalpha-caseininmilkandPrup3inpeachcouldbeshowninapres-
surerangeof200–600MPa(Lavillaetal.,2016;Ekezieetal.,2018).
Highpressurealonecouldnotmodifytheallergenicpropertiesofcarrots,peanut,milk,celery,apple(Jiménez-Saizetal.,2015).
Asitissuitableforothertechnologies,themosteffectivewaytoreducetheallergenicitybyhighpressureprocessingisthecombi-
nationwithotherprocessesthatactsynergistically.Onepossibilityistocombinepressureandheat,whichworkswell,butmore
effective seems to be thecombined treatment of high pressure and enzymic hydrolyzes during or after the treatment (Somkuti
andSmeller,2013;Jiménez-Saizetal.,2015;Meinlschmidtetal.,2016).Meinlschmidt(2016)studiedtheeffectonsoyprotein
isolate with an enzymatic hydrolysis during and after high pressure processing at pressures ranging from 100 to 600MPa at
50(cid:1)Candadwelltimeof15min.Itwasshownherethatacombinedprocessatpressuresfrom300to600MPacouldleadto
anearlycompletelossofimmunoreactivityofthementionedallergen.Further,theoilbindingandfoamingactivitywereenhanced.
SimilarresultsandstudiesaresummarizedbySomkuttiandSmeller(2013),e.g.,beta-lactoglobulinandovalbuminincombina-
tionwithpepsinledtoanincreasedhydrolysisat600MPaandafewminutesoftreatmenttime.ForpeanutallergenArah6no
changescouldbeshownat700MPaat20or80(cid:1)C.
Thepressurestabilityofallergenproteinsvariesgreatly,dependentontheirsecondarystructure,thesurroundingsandtreatment
conditionsapplied.Further,combinedstudiesareneededtoassesstheinfluenceandtheeffectivenessofpressure-enzymatichydro-
lyzesprocesses.Eventually,onlyprickteststudiesincombinationwithstructuralanalysisoftheallergenwillvalidatetheeffective-
nessofthereduction.
1.01.3.2 Toxins
Therearetwotypesoftoxinsthatareofinterestinfood.Onebeingthoseincorporatedduetotheuseofchemicalsduringgrowthof
crops(pesticidesandherbicides)aswellasthegenerationofmicrobiologicaltoxins,suchasaflatoxins,C.botulinumtoxin,etc.The
secondonebeingtoxinsthatariseduringtheprocessingofthefoodsduetoheattreatment,theso-calledfoodprocessingcontam-
inants(furan,acrylamide,HMF,MCPD-estersetc.)
1.01.3.2.1 Food Processing Contaminants
TheoccurrenceofFPCsinfoodsisnotnew,astheyhavealwaysexistedsincethefirstdayhumansstartedtoprepareandconserve
theirfoodsbyfireorheat.Nowadays,theawarenessofwhatthesecompoundscandowithinthehumanbodyismoreadvancedand
theanalyticaltoolsareavailabletoanalyzetheamountsofthesecompoundswithinfoodsinthemgkg(cid:6)1range(Sevenich,2016;
Sevenichetal.,2016).
Thehightemperaturesat>110(cid:1)Cneededduringthermalsterilizationfortheinactivationofsporesleadtotheformationof
unhealthycompoundswithinthefood.Sincethebeginningofthenewmillennium,moreattentionhasbeengiventothemech-
anisms and mitigation strategies of these compounds. The way of our foods from farm to fork or from raw material to better
OverviewofResearch Needs,Future andPotential ApplicationsofHigh-Pressure Processing 7
digestiblesafefoodsismadepossiblebyprocessessuchasheattreatment.Thosetreatmentsoftenresultinanover-processingand,
duetochemicalchangesintheproduct,givingrisetothefoodprocessingcontaminants(FPCs);synonymsare,process-induced
toxicants and neo-formed contaminants. FPCs only involve those compounds formed during the processing (heating, roasting,
frying,baking,grillingetc.)ofthefood.FPCsaresubstancespresentinfoodbecauseoffoodprocessing/preparationthatareconsid-
eredtoexertadversephysiological(toxicological)effectsinhumans,i.e.,substanceswhichposeapotentialorrealrisktohuman
health.Ingredientscommonlyoccurringinfoodformulationsareexcellentsubstratesforchemicalreactionsoccurringunderthe
conditionsencounteredinfoodprocessing.Thereactionproductsformeddependontheprocessesandconditionsused,suchas
fermentation,irradiation,orheatprocessing(StadlerandLineback,2009).Thecompoundsformedplayavitalroleinfoodprop-
ertiessuchasflavor,aromaandcolor.PrecursorsofFPCsaresugarsandaminoacids;otherreactionpathwayscaninvolvepoly-
unsaturated fatty acids (PUFAs; linoleic acid), ascorbic acid, sugars (glucose, fructose), glycerol, chloride or carotenoids (Crews
and Castle, 2007; Vranová and Ciesarová, 2009; Lachenmeier and Kuballa, 2010; Bravo et al., 2012; Crews, 2012). Therefore,
changingtherecipeoffoodsisnotanoptionsincesomeofthemostpotentprecursorsofFPCsareessentialnutrients,likepoly-
unsaturated fatty acids, reducing sugars, carotenoids, proteins etc. Compounds formed during the processing of food are, for
example, acrylamide, furan, 3-MCPD esters etc. These show carcinogenic, mutagenic (genotoxic), or neurotoxic properties at
highdosesinanimalstudies(BfR,2004,2012;Studeretal.,2004;Märketal.,2006;VranováandCiesarová,2009;Jestoietal.,
2009;Larsen,2009;StadlerandLineback,2009;LachenmeierandKuballa,2010;Palmersetal.,2014;Sevenichetal.,2015a,b;Ket-
tlitzetal.,2019).Therefore,ariskforhumans,especiallyforinfants,theelderlyandimmunesuppressedpersonisnotneglectable.
TheriskoftheexposuretoFPCsisnotanewone,sincehumansalwayshavebeenexposedtothesekindsofcompoundsfromthe
moment“theycaughtfire”.Nevertheless,thereisapublicconcernandthoserisksmustbeminimized(Curtisetal.,2013).Forgen-
otoxicandcarcinogenicsubstances,suchasfuranandacrylamide,theALARAprinciple(aslowasreasonablyachievable)isapplied
tofoodsasapossibleriskassessment(CrewsandCastle,2007).Nevertheless,thedatashownhereclearlyindicatesthattheFPCsof
majorconcerninfoodsareacrylamide,furanand3-MCPD.TheEuropeanCommissionandtheEuropeanFoodSafetyAuthority
(EFSA) have been monitoring different FPCs, especially acrylamide, furan (and its derivates), 3-MCPD and -esters and glycidyl
esters,inallkindsoffoodsoverthelastyearsandhavealreadyissuedbenchmarklevelsforacrylamidein2017(EU,2017).The
creationandintroductionofnewguidelinesinthefutureislikelyandwillbeadifficulttaskforthefoodindustry(EFSA,2013;
Kettlitz et al., 2019). Therefore, other technologies and research is needed to find mitigation strategies which lead to the same
quality without affecting the safety of the product. Here the high-pressure thermal sterilization or high-pressure pasteurization
(insteadofconventionalheattreatment),ohmicheatingandvacuumbaking,justtonameafewinnovativetechnologies,could
bepowerfultoolstoachievethisaim.Researchinalltheseareasisprogressingatarapidpaceandtheseselectedexamplesshow
thatprocesstoxicantshaveinthepastfewyearsgainedsignificantattentiononaglobalscaleintermsofpotentialhumanhealth
risk.InMarch2018,EFSAissuedacallforthecontinuouscollectionofchemicalcontaminantsoccurrencedatainfoodandfeed
(EFSA,2018).ThesedataareusedinEFSA’sscientificopinionsandreportsoncontaminantsinfoodandfeed.Thislastcallshows
howimportantitistolegislativeorganizationstobeontopofthissensitivematter.Thereareonlyafewstudiesavailablethatshow
themitigatinginfluenceofhigh-pressurethermalsterilizationonthereductioninrealfoodsystems.Sevenichetal.(2013)andSev-
enichetal.(2015a,b)showedthatareductionoffuranindifferentfoodsystems(vegetablebabyfoodandsardineinoliveoil)is
possiblewithHPTS(600MPa,90–121(cid:1)C)byupto95%incomparisontothermalsterilization.Palmersetal.(2014)alsoshowed
areductionoffuraninvariousvegetableblendsunderhighpressurethermalsterilizationconditions(600MPa,117(cid:1)C)incompar-
isontothermaltreatment.Tothispoint,thequestionifthepressure,followingtheLeChatelierprinciple,hasaninfluenceonthe
formationpathwayofthesecompoundsisstillunanswered.IntheopinionoftheauthorsthereductionofFPCscanbesolelyattrib-
utedtothelowerthermalloadappliedtotheproduct.Forhighpressurepasteurizationtheformationoffoodprocessingisnotan
issuesincethethresholdtemperaturesofabove110(cid:1)Corhigherarenotreached.
1.01.3.2.2 Aflatoxins, Pesticides andHerbicides
Tothisdatethereisnoliteratureavailablehowhigh-pressureprocessingaffectsordestroyseitheraflatoxinsorpesticidesandherbi-
cides.Itwillbeinterestingtoinvestigatethesecompoundsandhowtheymaybealteredbyhighpressureprocessing.Aflatoxinfor
exampleisverytemperaturestableandstartsdecomposingattemperaturesbetween237and306(cid:1)C(Kumaretal.,2017)butaheat
treatmentbetween90and120(cid:1)Ccanalreadyreducetheamountofaflatoxinasmuchas25%–65%.Therearesomestudiesinthe
publicdomainonprocessingbyextrusioncookingofpeanutandricemealattemperaturesof140–200(cid:1)Candpressuresinthe
extruder of 30–60bar. The highest aflatoxin reduction was found to be 51%–95% with a moisture content of 35% in peanut
meal, and the extrusion variables did not significantly affect its nutritional composition (Castells et al., 2006; Kumar et al.,
2017).ItisworthwhiletoinvestigatetheeffectofHPTSandHPPonaflatoxins.Therewasnopublicationfoundoninfluenceof
high-pressureprocessingonpesticidesorherbicides.
1.01.4 Process-Structure-Relationship
Highpressureprocessingcanalterthepropertiesofmacromoleculeslikestarch,pectinandproteinsandcombinationsoftheafore-
mentionedcompounds.Therefore,itcanbeofgreatinteresttocreatenewtextures,whichcouldleadtothedevelopmentofnewand
excitingstructures.Thisisnotonlytodesignnewfoodsbutalsotoevaluatehowtheprocessinfluencesproductsintermsoftexture
andstructurethatusuallywouldhavebeenthermallytreated.Thereissignificantinterestinunderstandingtheeffectsofhighpres-
sureonfoodandfoodingredients,toanticipatefurtherapplicationsofthetechnology(ETP,2007;SunandHolley,2010).The
followingsectionwillsummarizeongoingresearchactivitiesandneedsinthisfield.
8 Overview ofResearch Needs,Future andPotential ApplicationsofHigh-Pressure Processing
1.01.4.1 Starch
Starchisoneofthemajorcarbohydratesusedinthefoodindustryandinhumandiet.Asasourceofenergyandamajorsourceof
carbon,starchisanessentialpartofhumannutrition.Inthefoodindustry,starchservesasathickeningandgellingagent,e.g.,for
saucesandpuddings.Starchanditsderivativesarealsoimportantinthechemical,textileandpaperindustries.Itisobtainedfrom
thereserveorgansofplants.Wheat,potatoes,maizeandtapiocaarethemostimportantrawmaterialsinglobalstarchproduction.
Asalreadymentioned,ultra-highpressurehasasignificantimpactonthephysicalandchemicalpropertiesofmacromolecules.In
termsofcarbohydrates,ultra-highpressureleadstogelformation,aloweringofthegelationtemperature, areducedenzymatic
stabilityofstarchandlittleornoMaillardreactionatroomtemperature(Hendrickxetal.,2001).Partialswellingandgelatinization
ofstarchcanoccurunderhighpressureconditionsevenatroomtemperature(Stute,1999;Douzalsetal.,2001;Katopoetal.,2002).
Therequiredtreatmentparameters,suchaspressure,temperature,holdingtimeandwaterconcentrationdependtoalargeextenton
thetypeofstarch(Autio,1998;BauerandKnorr,2005).Thegelatinizationunderultra-highpressureatroomtemperatureisaccord-
ing to Rubens et al. (1999) described similar to thermal gelatinization by a 2-step mechanism. First, the amorphous areas are
hydrated, which loosens the crystalline structures and swells the grain. In the second step, the crystalline areas are increasingly
brokenupandhydrated.Onlyasmallamountofamyloseleakagefromthegrainscanbeobserved.Stoltetal.(1997)alsodescribe
stabilizationofthecrystallineareasthroughinteractionswiththeremainingamylose.HydrogenbondsandvanderWaalsforcesare
likelystabilizedbyultra-highpressure,whichinturnfavorsthedoublehelix(Buckowetal.,2007).Thegranularcharacterofthe
grainsislargelyretainedduringtheultra-highpressuretreatment(Hayashi,1992)andthereisnocompletedisintegrationofthe
structureasinthecaseofthermalgelatinization.Thus,thepressure-induced,pastytosolidstarchgelscanonlybereferredtoas
particlegels,whichdonotformarealgelnetwork.Inaddition,thethermallyformedstarchgelsandpastehaveamuchhigher
strength or viscosity (Buckow et al., 2007). Interestingly, the starch grains lose the double refraction despite no degradation of
thecrystallinestructures.Itbecomesclearthattheprocessdescribedrequiresanexcessofwatermoleculesandisthereforeheavily
dependentonthewatercontent.Additionsofwater-bindingsubstancessuchassugarorsaltscanthereforehaveasignificantimpact
onthehigh-pressure-inducedswelling.RumpoldandKnorr(2005)showedthatthepreviouslydescribedinfluenceofthenumber
ofequatorialgroupsalsoexistsinthecaseofswellingandgelatinizationinducedbyhighpressure.Starcheswithahighamylose-
amylopectinratio,suchaswheatorpotatoes,haveveryhighpressureresistance(Hendrickxetal.,2001).Waxystarchestherefore
showlittleresistancetopressure(Simoninetal.,2009).Stute(1999)usedlossofbirefringencetoshowthatpressureresistanceis
alsovisibleintheX-raydiffractionpattern.Accordingly,mostlyB-typestarchesaremorepressure-resistantthanthoseoftheAandC
types,butduetooverlaps,acleardistinctioncannotbemadeinthisregard(Rubensetal.,1999;Katopoetal.,2002).X-raystructure
analysesalsoshowedthatanX-raydiffractionpatternchangeduringultra-high-pressuretreatmentcanoccur.Forexample,nativeA-
typestarchesshowtheX-raydiffractionpatternofB-typestarchesaftertreatment,withthelatterundergoingnochange(Hibietal.,
1993;Katopoetal.,2002).Accordingtotheauthorsmentioned,thischangeisduetothestructureoftheamylopectin.Asalready
mentioned, B-type starches have channels between the double helices in which a large number of water molecules can be
embedded.Underultra-high-pressureconditions,theseinteractwithandstabilizethedoublehelices.Duetothemolecularflexi-
bilityoftheA-typedoublehelices,thesecanformchannelsunderultra-high-pressureconditions.Incombinationwiththethermal
process,gelatinizationunderultra-highpressurecanbeachievedbelowtheatmosphericgelatinizationtemperaturesinceultra-high
pressurelowersit.Asthetemperaturerises,thispressureeffectbecomesweaker(Buckowetal.,2007).
Thefeatureshighpressuretreatedstarchofdifferentplant-basedoriginsofferarenotfullyassessedandused.Onepossibility
couldbetousethetexturetodesignandbuildlowfatfoodssincethegelshaveamouthfeellikefat.Furtherstarchincombinations
withe.g.proteinscouldbeusedtocreateahybridnetworksofstarchandproteinstodevelopmeatfreeplant-basedproteinrichand
fiberrichfoods.Duetothenatureofthestarchafterthetreatment,thestarchwouldberesistantandthereforethefoodwouldhave
alowglycemicindex.Papathanasiouetal.(2015)showedthat5%starchsolutionsofwheat,tapioca,potato,corn,waxycornand
resistantstarch(RS3)releasedlessglucoseafter120minofenzymaticdigestionsiftheywerepressurizedat600MPafor15minat
roomtemperatureincomparisontoheattreatedstarchsolutions.
1.01.4.2 Pectin
Pectinismainlyfoundinplant-basedproducts.Herethehighestamountsarefoundinapple(1.5%w/w)andcarrots(1.4%w/w).
Inprocessing,pectin,whichismainlyfoundinthemiddlelamella,canbealteredbyeitherchemicalorbiochemicalconversions.
Thiscanbeinfavorofthetexture(demethoxylation)ordetrimental(depolymerization/beta-elimination)(VanDerPlanckenetal.,
2012).Demethoxylationofpectincaneitherbetriggeredbynon-enzymaticorenzymaticdemethoxylation(Pectinmethylesterase,
PME).Inthecaseofhigh-pressureprocessing,bothmechanismscouldbepresentsimultaneouslysincetheprocessdoesnotaffect
PMEtosuchanextentthatitwouldbefullyinactivated.Therateofthisreactionisacceleratedwithincreasingdegreesofmethyl-
ation,temperature,andpH(4–6)(Diazetal.,2007).EspeciallythepHforfruitandvegetable-basedproductsisatanoptimum.For
non-enzymatic degradation of pectin there are two mechanisms that could apply:beta-elimination or demethoxylation by acid
hydrolysis (Van Der Plancken et al., 2012; Chen et al., 2015). The ß-elimination reaction is primarily base-catalyzed, but can
alsobecomedominantatpH>4,andleadstothecleavageataglycosidiclinkagenexttoanesterifiedgalacturonicacid;asaresult,
pectinwithahighdegreeofmethoxylation(DM)ismoresubjecttoß-eliminationthanpectinwithalowDM(Chenetal.,2015).At
lowdegreeofmethoxylation(DM),demethoxylationcanalsooccurbyacidhydrolysis,enhancedbytemperaturebutnotbypres-
sure.TwopossibleexplanationsweresuggestedfortheimprovedretentionofhardnessunderpressurebyVanderPlanckenetal.