Chemistry Reference
In-Depth Information
below the freezing point (Penield and Campbell 1990). Thus, lowering the storage temperature
abovethefreezingpointincreasesthestalingrate.Finally,stalingofbreadispartlyreversiblewhen
heated.
Severalanalyticaltechniqueshavebeenusedtounderstandandcontrolstarchretrogradation,as
wellasstarchgelatinizationpreviouslyreferred,duringfoodprocessingandstorage,forexample,
DSC,X-raydiffraction,NMR,rheologicalanalysis,FTIR,andRamanspectroscopyandmicros-
copy(Liu2005).
Technology of starch
:Starchiswidelyusedinthefoodindustrybecauseofitsuniqueproper-
ties.Cornisconsideredthemainsourceforstarch.Thecommonprocedureusuallyfollowedfor
starch production is as follows: corn is steeped for 35-45 h in water at 15°C with suficient SO
2
(0.15%-0.20%)addedtopreventgrowthofmicroorganismsandstartthedisintegrationofprotein.
Duringsteeping,thecornpicksupwaterandisthenreadilygroundtoseparatehullsandgerm.The
starch, protein, and water-soluble substances form a slurry that is separated from the germ. The
slurryistheninelygroundandseparatedfromhullsandcoarseparticles.MoreSO
2
isthenadded,
andthetemperatureincreasedtowithintherangeof29°C-33°Ctomakeeasiertheseparationof
thestarchgranulesfromaproteinaceousmaterial.Thegranulesareseparatedbyvariousmethods
suchascentrifugationorilteringandarewashedanddried(Meyer1987).
Modiied starches
:Starchcanbemodiiedinordertoincreaseitsfunctionalityandeficiency
as a thickening agent and obtain properties necessary for speciic uses in food systems. Natural
starchescanbemodiiedbyphysicalandchemicalmeans(PotterandHotchkiss1995).Typesof
modiications that are most often made, sometimes singly, but often in combinations, are cross-
linking of polymer chains, noncross-linking derivatization, depolymerization, and pregelatiniza-
tion.Speciicpropertyimprovementsthatcanbeobtainedbypropercombinationsofmodiications
arereductionintheenergyrequiredtocook(improvedgelatinizationandpasting),modiicationof
cookingcharacteristics,increasedsolubility,eitherincreasedordecreasedpasteviscosity,increased
freeze-thawstabilityofpastes,enhancementofpasteclarity,increasedpastesheen,inhibitionof
gelformation,enhancementofgelformationandgelstrength,reductionofgelsyneresis,improve-
ment of interaction with other substances, improvement in stabilizing properties, enhancement
ofilmformation,improvementinwaterresistanceofilms,reductioninpastecohesiveness,and
improvementofstabilitytoacid,heat,andshear(BeMillerandWhistler1996).
The cold-water-soluble starch (pregelatinized) and the cold water swelling starch (CWS) are
twotypesofinstantstarchthatresultfromstarchmodiicationbyphysicalmeans.Pregelatinized
starchiswidelyusedinthefoodindustrybecauseofitsabilitytoactasathickeningagent,thus
increasingtheviscosityoftheproductandgeneratingapulpytexture.Pregelatinizationisarela-
tively simple modiication treatment that makes starches dispersible in cold water. In pregelati-
nized starch, gelatinization precedes and drying follows. It can be produced by spray cooking,
drumdrying,solvent-basedprocessing,andextrusion(Xieetal.2005).Bothchemicallymodiied
andunmodiiedstarchescanbeusedtomakepregelatinizedstarches.Pregelatinizedstarchesare
usefulinthefoodindustry(mainlyininstantfoods),astheygelatinizebyswellingeasilyevenin
wateratroomtemperature.AnothertypeofinstantstarchisreferredtoasCWS.Granularstarch
thatswellsextensivelyincoldwaterismadebyheatingcommoncornstarchin75%-90%ethanol
orbyaspecialspray-dryingprocess(BeMillerandWhistler1996).Itdiffersfrompregelatinized
starchinhavingintactgranulesand,therefore,greaterstabilityandbettertexture(Luallen1985).
Mechanicallymodiiedstarchesandextrudedstarchesarealsostarchesmodiiedbyphysicalmeans
(Belitzetal.2009).
Many chemical treatments are used to modify starch. Chemically modiied starches are the
productsofthetreatmentofanyofseveralgrain-orroot-basednativestarcheswithsmallamounts
ofcertainchemicalagentsthatmodifythephysicalcharacteristicsofthenativestarchestoproduce
desirableproperties.Differenttreatmentsappliedcanbeclassiiedasmildoxidation(bleaching),mod-
erateoxidation,aciddepolymerization,monofunctionalesteriication,polyfunctional esteriication
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